High-speed shimmy, Speed wobble
Shayne Wissler
Aires started to get a bad speed wobble. This is the first time it's ever
happened (and I've been at that speed many times over the summer).
I've read about speed wobbles but have never experienced one. At first I
thought my front tire had gone completely flat and was going out of control,
or as if the front tire had become extremely out of true--I'd guess that the
wobble amplitude was about 2-3", and a frequency of about 5Hz. But the
braking was responsive. As I slowed down it continued to wobble for a while
though lower speeds (I'll guess through 30MPH--but I don't know). I finally
stopped, checked that my front tire was in tact and not out of true.
Everything appeared OK, so I continued down the hill, this time not going
over 30 or so.
My owners manual says that if I experience this, to take it into the shop. I
called the shop and they want to see the bike. But based on my reading of
the shimmy FAQ, I'm half expecting that they won't find anything.
I have made two changes to my bike recently. The most recent was that I
lowered my handlebars by about 2". They used to be almost parallel to my
seat. I did tighten the headset well. The other is that I replaced my front
tire with a lighter, skinnier one.
I have descended with the tire before, but I can't say whether I reached
42MPH or not. I can say that ever since I put that tire on, I have noticed
there being less stability while riding no-hands--it does start to shimmy a
little, but at lower speeds and not so violently. Is it probable that this
low-speed (~20MPH?) no-hands shimmy is from the same source as the violent
shimmy?
Any suggestions would be appreciated.
Shayne Wissler
Werehatrack
<thalesN...@yahoo.com> may have said:
>Is it probable that this
>low-speed (~20MPH?) no-hands shimmy is from the same source as the violent
>shimmy?
>
>Any suggestions would be appreciated.
Observing that the problem appeared after the tire change, the
connection to the reduced diameter is possible but not proven.
An observation: Reducing the diameter of the front tire will move the
steerer axis more toward the vertical, which moves the point of
intersection of the steerer axis with the ground toward the tire's
contact patch. The distance between the axis intersection and the
patch is the "trail" of the fork. Insufficient trail will cause
exactly the problem that you describe...but if the amount of trail
before the tire swap was small enough that the change produced this
problem, I would be a bit surprised. If the bike has a suspension
fork, try cranking the preload up to the max, as that will tend to
minimize such a problem.
Somehow, though, I think the lbs is likely to find that there is
something else wrong. What I describe is, in my opinion, not terribly
likely to be the problem.
--
My email address is antispammed;
pull WEEDS if replying via e-mail.
Yes, I have a killfile. If I don't respond to something,
it's also possible that I'm busy.
Mike Jacoubowsky
> thought my front tire had gone completely flat and was going out of
control,
> or as if the front tire had become extremely out of true--I'd guess that
the
> wobble amplitude was about 2-3", and a frequency of about 5Hz. But the
> braking was responsive. As I slowed down it continued to wobble for a
while
> though lower speeds (I'll guess through 30MPH--but I don't know). I
finally
> stopped, checked that my front tire was in tact and not out of true.
> Everything appeared OK, so I continued down the hill, this time not going
> over 30 or so.
Once you get a shimmy, my advice is not to slow down, but stop, take a
breather, and then get going again. Lack of confidence doesn't help the
situation any.
> I have made two changes to my bike recently. The most recent was that I
> lowered my handlebars by about 2". They used to be almost parallel to my
> seat. I did tighten the headset well. The other is that I replaced my
front
> tire with a lighter, skinnier one.
Simplest experiment would be to raise the bars back up again and see if the
shimmy goes away. As you've read in the FAQ, shimmy isn't a function of the
bicycle alone, but the entire system, which includes you on it. The
combination of your position being altered and the skinnier tire (which
speeds up response on the front end) sounds like a good place to start,
almost a no-brainer.
--Mike-- Chain Reaction Bicycles
http://www.ChainReactionBicycles.com
"Shayne Wissler" <thalesN...@yahoo.com> wrote in message
news:70Zdb.634208$o%2.291570@sccrnsc02...
jim beam
i used to have similar experiences on an older road frame and i managed
to "tune" it out.
as you read in the faq, there are many reasons for the shimmy, but
basically, you're looking at a dynamic system which has a resonance,
just like that famous footage of the tacoma narrows bridge.
the initiation of the resonance aside, and tires are one, the frame and
the wheels facilitate the resonance. just like the bridge, the wind
initiated the oscillation, but the resonant frequency of the bridge was
disasterously "in tune".
so, if you are to address this problem with your bike, you have to
address these two main areas - frame & wheels. i was lucky enough to
have several rear wheels and noticed that different wheels had different
effects on the resonance. in my case, the lighter spoked wheels were
much more prone then the heavier spoked ones. following this pattern, i
ended up building a "stiff" rear wheel with straight gauge 2.0mm spokes
on the drive side and butted 2.0/1.8/2.0mm on the non-drive. it's very
rigid and quite a harsh ride, but it killed the shimmy completely.
i have since replaced that frame and can report that while i can induce
some degree of shimmy in any of the three others i now have if i really
try, none of them are susceptible in the same way.
ymmv, but in my opinion, start with wheel variants and if that doesn't
work, move on to a different frame. my aluminum frame is the most stable.
jb
David L. Johnson
> My owners manual says that if I experience this, to take it into the shop.
> I called the shop and they want to see the bike. But based on my reading
> of the shimmy FAQ, I'm half expecting that they won't find anything.
>
Quite lkely.
> I have made two changes to my bike recently. The most recent was that I
> lowered my handlebars by about 2". They used to be almost parallel to my
> seat. I did tighten the headset well. The other is that I replaced my
> front tire with a lighter, skinnier one.
The maddening thing about shimmy is that it can be just about anything
that will cause, or cure, it. It's as likely the bar height (and the
change in your position that results) as the tire.
>
> I have descended with the tire before, but I can't say whether I reached
> 42MPH or not. I can say that ever since I put that tire on, I have noticed
> there being less stability while riding no-hands--it does start to shimmy
> a little, but at lower speeds and not so violently. Is it probable that
> this low-speed (~20MPH?) no-hands shimmy is from the same source as the
> violent shimmy?
I'd say it's possible.
>
> Any suggestions would be appreciated.
Try it with the bars a bit higher, or with another front tire. If it
_does_ shimmy, press one knee against the top tube. That should stop it.
Also, unloading your weight from the saddle will stop the shimmy.
--
David L. Johnson
__o | "Business!" cried the Ghost. "Mankind was my business. The
_`\(,_ | common welfare was my business; charity, mercy, forbearance,
(_)/ (_) | and benevolence, were, all, my business. The dealings of my
trade were but a drop of water in the comprehensive ocean of my
business!" --Dickens, "A Christmas Carol"
Claire Petersky
> The other is that I replaced my front
> tire with a lighter, skinnier one.
I bet this is it. When I developed a "high-speed" no-hands shimmy
earlier this year, I read everything on rb* on shimmies. It seemed
like the fact I had replaced the rear tire with a slightly fatter one
was the likely culprit. I returned to a skinnier rear tire, and the
high speed shimmy disappeared.
Warm Regards,
Claire Petersky (cpet...@yahoo.com)
Home of the meditative cyclist:
http://home.earthlink.net/~cpetersky/Welcome.htm
Books just wanna be FREE! See what I mean at:
http://bookcrossing.com/friend/Cpetersky
Callistus Valerius
> >low-speed (~20MPH?) no-hands shimmy is from the same source as the
violent
> >shimmy?
> >
> >Any suggestions would be appreciated.
I'll tell you this just once, and I assume you don't want the sh*t
scared out of you again. The skinny tire did it. Put a 25 width tire on
the front and enjoy life.
Callistus Valerius
> like the fact I had replaced the rear tire with a slightly fatter one
> was the likely culprit. I returned to a skinnier rear tire, and the
> high speed shimmy disappeared.
It doesn't matter what you have on the back wheel, it's the front wheel
that counts.
jobst....@stanfordalumni.org
of these testimonials is how and at what speed these shimmy episodes
occurred. In prior airing of this sort of thing, it was claimed that
balancing the front wheel would prevent shimmy or that a different
weight wheel would do it.
I put a large imbalance on a front wheel and made test runs with and
without imbalance (I balanced the wheel as well as greatly imbalanced
it) with no discernable difference in shimmy. I use a 5% grade,
smooth half mile section of road, coasting at between 25 and 30 mph
no-hands and can consistently develop shimmy.
The next test was to completely fill the front tire with water. This
changed the shimmy frequency slightly but did not stop it from
occurring.
That said, I descend mountain roads often at speeds up to 50mph with
no problem while placing my hands on the stem, knees together. Shimmy
is a characteristic of most larger bicycle frames and should not be
allowed to occur by the rider. SInce most people cannot ride
no-hands, they are not aware of the tendency of their bicycle to
shimmy. Then when it occurs, it is a disaster about to happen.
http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html
Jobst Brandt
jobst....@stanfordalumni.org
Tom Nakashima
choice at first.
I just built a bicycle with upright steel handlebars (older schwinn type)
using an older Specialized Expedition touring bike (long wheelbase). The
wheels are Mavic MA-2 with Campagnolo 36h hubs, 126mm spacing in the rear
13-24 6sp. The tire are the older Avocet Duro Plus 32's, tire pressure 85
psi.
On a descent grade of 3-6 % for about 1/3 mile I was able to induce shimmy
with my hands on the handlebars.
My speed was 26-32mph.
I've also noticed that with upright bars the steering is very responsive
from what I was used to, riding drop bars.
I'm not sure if this is because of the handlebars being further behind the
stem. In any-case it was easy to induce shimmy.
I thought this was interesting, so I rode back up the hill and repeated it
again. As I got the bike to shimmy I wanted to see if I could correct this.
I took weight off the handlebars by every so slightly removing both hands
about an inch away from the bar. My speed was about 27 mph, and before I
knew it, the shimmy corrected itself and was completely eliminated.
I repeated this a 3rd time, to make sure it wasn't a fluke and actually
timed how long it took for the shimmy to correct itself. The time was about
5 to 7 seconds for the shimmy to completely vanish.
I'm going to try this again since it's one of my training routes. This time
I changed tires, with Avocet Carbon 12 Road 700 x 25c.100psi.tire pressure.
These are the tires I normally ride with my roadbike. Strange, but my
roadbike doesn't shimmy at all on this stretch of my training ride.
-tom
<jobst....@stanfordalumni.org> wrote in message
news:%fkeb.26215$dk4.8...@typhoon.sonic.net...
Sam Huffman
> On a descent grade of 3-6 % for about 1/3 mile I was able to induce shimmy
> with my hands on the handlebars.
I have had a similar experience (to this, and to the OP) recently. I replaced
my Avocet Fasgrip 700x28 tires (to tie into yet another thread, the rear was
completely worn through after 1500 miles, 120000 feet of climbing) with an
Avocet Criterium 700x23 (the "real" 28 doesn't fit my frame, and I couldn't
find a 25).
The second day out, riding no-hands at 35-40 mph I had an extremely violent
wobble, far worse than the shimmy I've had before at around 18mph. I've
since noticed that I feel this wobble even with my hands on the bars, though
it's easily controlled in this situation.
This was contrary to what I've read here and in the FAQ, which seems to imply
that shimmy doesn't happen with one's hands on the bars. Changing my position
on the bike, including using the aero bars, makes little difference. Unlike
yours, my shimmy seems not to self-correct, though I have only let it go for
1-2 seconds because it feels like it's about to throw me off the bike at
40mph, and that's bad for morale.
Sam
Erik Brooks
> On Mon, 29 Sep 2003 16:23:31 +0000, Shayne Wissler wrote:
>
> > I have made two changes to my bike recently. The most recent was that I
> > lowered my handlebars by about 2". They used to be almost parallel to my
> > seat. I did tighten the headset well. The other is that I replaced my
> > front tire with a lighter, skinnier one.
>
> The maddening thing about shimmy is that it can be just about anything
> that will cause, or cure, it. It's as likely the bar height (and the
> change in your position that results) as the tire.
>
I've encountered shimmy exactly once, after I assembled a used eBay
bike and took a first ride. I had not tightened the handlebars
enough. I found this when I went quickly over a rise in the road on a
downhill. I didn't get airborne, but I did get very light, and then
came down upon the bars with some force, which caused them to rotate
down and lower my hand position by several inches. For a few seconds
I could not reach the brake levers. I beleive that my speed was
basically unaltered - the only real change in the dynamics of the bike
was that my mass on the front of the bike was noticably lower. The
resulting shimmy was immediate and violent, but stopped quickly with
the knees on the top tube method.
From this I think it is possible that your problem may be caused by
lowering your bars alone, or from the combo of the two. I'll second
the recommendation that you set the bars back up and try the same hill
with the new tire.
Good luck.
Erik Brooks
Seattle
David Mackintosh
I've read the FAQ and everything else I could find on this subject,
and what seems apparant is that nobody has a really good handle on the
causes of the usually mild no-hands shimmy that many bike/rider
systems exhibit, or the much more violent "deathwobble" hands-on
headshake that, fortunately, only a few of us seem to experience.
Weight distribution, steering geometry, and structural variable may
all contribute to varying degrees.
My daily rides involve descents that allow me to easily reach 50mph,
and I've been up to about 58mph. I can ride comfortably no-hands and,
on many bikes, easily find the no-hands shimmy speed, and then stop it
with a knee, or by putting one hand on the bar. This shimmy is mostly
just annoying when one is trying to open a snack or take off a jacket
while riding near the shimmy speed. Ideally, a bike would not do it
at all.
I don't know if the deathwobble is related or not. This most often
occurs at higher speeds (35mph+), rough pavement, and while braking
hard in a straight line, or lightly through the first half of a
corner. It seems to happen less frequently if I concentrate on
maintaining a very light grip on the bars, but on bumpy pavement this
is not always possible. Also, the grip on the bars and forward weight
transfer while braking may set it off. It is not easily stopped by
the methods mentioned in the FAQ, and makes steering control very
difficult. Usually, I just have to brake hard enough to slow the bike
out of the deathwobble zone and hope that I don't run out of road.
This seems to be more common on larger, more flexible frames, but I've
also experienced it of very rigid frames, which leads me to suspect
it's also related to steering geometry or weight distribution.
Suggestions I've heard include very stiff top tubes, and more relaxed
head angles (almost all large frames have 74 degree head angles) with
longer rake forks.
-David
Shayne Wissler
"Sam Huffman" <shuf...@ichips.intel.com> wrote in message
news:po8fzie...@pdxlx1644.pdx.intel.com...
> The second day out, riding no-hands at 35-40 mph I had an extremely
violent
> wobble, far worse than the shimmy I've had before at around 18mph. I've
> since noticed that I feel this wobble even with my hands on the bars,
though
> it's easily controlled in this situation.
>
> This was contrary to what I've read here and in the FAQ, which seems to
imply
> that shimmy doesn't happen with one's hands on the bars. Changing my
position
> on the bike, including using the aero bars, makes little difference.
Unlike
> yours, my shimmy seems not to self-correct, though I have only let it go
for
> 1-2 seconds because it feels like it's about to throw me off the bike at
> 40mph, and that's bad for morale.
Sounds like my experience: 42MPH and a very violent wobble. And my hands
were definitely on the handlebars (I was descending a canyon and going
fast).
I wonder if it has anything to do with reduced spoke count wheels. My front
wheel has 20 spokes.
Shayne Wissler
Shayne Wissler
> I wonder if it has anything to do with reduced spoke count wheels. My
front
> wheel has 20 spokes.
Here is a thought: At 42MPH, the wheel rotates at about 9 times per second.
This is in the frequency range of the wobble I experienced (I guessed 5, but
it could have been 9). A reduced spoke count wheel is going to have less
lateral stability than a wheel with more spokes, and so will have more
tendency to vibrate laterally at lower frequencies. Perhaps this wobble is a
lateral vibration of the rim itself, and it happens at the particular speed
where the wheel rotation rate corresponds to the frequency of vibration.
If this were happening it would explain the violence of the wobble. It is
hard for me to imagine how it could have been so radical if the wheel were
not bending, storing the energy of the oscillation. The question is: how
would one test this hypothesis?
Someone brought up the Tacoma Narrows bridge. Perhaps this example is even
more apt: maybe this death-wobble is caused from designing rims that aren't
stiff enough.
Shayne Wissler
Shayne Wissler
"David Mackintosh" <fallz...@hotmail.com> wrote in message
news:d3f7e4e3.03093...@posting.google.com...
All of this seems consistent with my hypothesis:
> I don't know if the deathwobble is related or not. This most often
> occurs at higher speeds (35mph+), rough pavement, and while braking
> hard in a straight line, or lightly through the first half of a
> corner.
Weight shifting onto the front wheel would cause a greater lateral
deflection, storing more energy in the front wheel. If the braking was
absolutely straight and the wheel were absolutely true, this wouldn't
happen, but neither are ever the case. Rough pavement would be more prone to
setting up the lateral vibrations in the rim.
> It seems to happen less frequently if I concentrate on
> maintaining a very light grip on the bars, but on bumpy pavement this
> is not always possible.
A light grip could easily correspond to less weight on the front wheel.
> Also, the grip on the bars and forward weight
> transfer while braking may set it off.
Yes...
> It is not easily stopped by
> the methods mentioned in the FAQ,
If my hypothesis is right, it is not at all the same shimmy, so the same
methods would not work. Moving your knee against the top tube would not
dampen much if the vibration is mostly going on in the rim itself. In fact,
if my hypothesis is right, the correct action is to shift some weight off of
the front tire, not off of the seat (actually the correct action is to get a
stiffer rim).
> and makes steering control very
> difficult. Usually, I just have to brake hard enough to slow the bike
> out of the deathwobble zone and hope that I don't run out of road.
This is what happened to me. The front of the bike was violently vibrating
from side to side. It seemed to be the rim (I suspected a flat and/or a
severely bent rim).
> This seems to be more common on larger, more flexible frames, but I've
> also experienced it of very rigid frames, which leads me to suspect
> it's also related to steering geometry or weight distribution.
If it's the front rim, the frame would make little difference.
> Suggestions I've heard include very stiff top tubes, and more relaxed
> head angles (almost all large frames have 74 degree head angles) with
> longer rake forks.
A longer fork might help, if it absorbed some of the energy of the lateral
vibration.
Shayne Wissler
Sam Huffman
> "Shayne Wissler" <thalesN...@yahoo.com> wrote in message
> news:pireb.2020$%h1.2293@sccrnsc02...
>
> > I wonder if it has anything to do with reduced spoke count wheels. My
> front
> > wheel has 20 spokes.
>
> Here is a thought: At 42MPH, the wheel rotates at about 9 times per second.
> This is in the frequency range of the wobble I experienced (I guessed 5, but
> it could have been 9). A reduced spoke count wheel is going to have less
> lateral stability than a wheel with more spokes, and so will have more
> tendency to vibrate laterally at lower frequencies. Perhaps this wobble is a
> lateral vibration of the rim itself, and it happens at the particular speed
> where the wheel rotation rate corresponds to the frequency of vibration.
I've got 36 spokes. Do I need to add 4 more?
Sam
Werehatrack
<thalesN...@yahoo.com> may have said:
>I wonder if it has anything to do with reduced spoke count wheels. My front
>wheel has 20 spokes.
It has been happening to people since long before 20-spoke wheels were
available.
It appears that there must be a substantial number of variables that
can, individually or in combination, have an effect on the presence
and severity of the problem...but it does not appear that there is any
established methodology for evaluating the possible factors and
identifying the cause in any given case, beyond the "try this stuff
and see what works" approach.
jobst....@stanfordalumni.org
>> That said, I descend mountain roads often at speeds up to 50mph with
>> no problem while placing my hands on the stem, knees together. Shimmy
>> is a characteristic of most larger bicycle frames and should not be
>> allowed to occur by the rider. Since most people cannot ride
>> no-hands, they are not aware of the tendency of their bicycle to
>> shimmy. Then when it occurs, it is a disaster about to happen.
> I've read the FAQ and everything else I could find on this subject,
> and what seems apparent is that nobody has a really good handle on
> the causes of the usually mild no-hands shimmy that many bike/rider
> systems exhibit, or the much more violent "deathwobble" hands-on
> headshake that, fortunately, only a few of us seem to experience.
> Weight distribution, steering geometry, and structural variable may
> all contribute to varying degrees.
I think you missed the point that bicycle shimmy is in the frequency
of normal human shivering, something that is related to the natural
response of the human muscles. Therefore, trying to resist shimmy by
grabbing the bars firmly and attempting to counter the oscillation can
easily lead to amplifying it. My early experience in this matter was
that a friend could not get started on a cold morning before breakfast
because he shimmied before the bicycle got moving and it only got
worse from there.
I believe that the terrified "death grip" is a major contributor to
shimmy because the tense muscles naturally respond in the shimmy
frequency. When I have ridden too far without food and a warm up in
cold weather, I can detect the tendency to shimmy on descents and I
take every precaution to not get caught in the feedback loop. This
includes a loose grip on the bars.
Jobst Brandt
jobst....@stanfordalumni.org
Shayne Wissler
"Werehatrack" <rau...@earthWEEDSlink.net> wrote in message
news:odlknvcckk4cf85tt...@4ax.com...
> On Wed, 01 Oct 2003 02:51:01 GMT, "Shayne Wissler"
> <thalesN...@yahoo.com> may have said:
>
> >I wonder if it has anything to do with reduced spoke count wheels. My
front
> >wheel has 20 spokes.
>
> It has been happening to people since long before 20-spoke wheels were
> available.
The shimmy *and* the violent wobble? I'm not convinced they're the same
thing. When I've observed shimmy, it was more diffuse vibration (the headset
moving from side to side), the wobble seemed quite focused on the front
tire.
> It appears that there must be a substantial number of variables that
> can, individually or in combination, have an effect on the presence
> and severity of the problem...but it does not appear that there is any
> established methodology for evaluating the possible factors and
> identifying the cause in any given case, beyond the "try this stuff
> and see what works" approach.
Well this just won't do. We live in a day and age where science and
technology can answer such questions--assuming the interested parties take
interest. Maybe back in the 60's such a stance made sense, but we've got all
sorts of fancy methods and tools for dealing with these kinds of problems.
How many physics PhD's have looked into this issue? What tests have been
run? Has there been any scientific approach at all to this issue, or is it
only individual cyclists that have built up an unscientific lore about the
shimmy?
I would assume that companies like Trek would care about whether their
products were safe, and put at least some R&D into this issue. Indeed, it
seems like a good opportunity to make some extra cash: if they figure out
the problem, and keep the answer proprietary, they can offer bikes that are
guaranteed not to wobble. In any case, it doesn't help business to have some
people scared out of the sport, or worse. And it doesn't help for cyclists
to take a passive stand on the issue and just accept wobbling bikes.
Shayne Wissler
Shayne Wissler
<jobst....@stanfordalumni.org> wrote in message
news:HKseb.26353$dk4.8...@typhoon.sonic.net...
> I think you missed the point that bicycle shimmy is in the frequency
> of normal human shivering, something that is related to the natural
> response of the human muscles.
Just because the shimmy frequency is close to the shiver frequency does not
imply that shivering or other muscle instability causes a shimmy. I have
descended this particular canyon many times, and this time was not
particularly cold, nor was I nervous or particularly tired. The bike was
definitely doing this vibrating on its own, though certainly my weight
distribution at that particular speed could have been a factor. I was part
of the system, but the instability was in the bike.
Shayne Wissler
Alex Wheaton
Shayne Wissler wrote:
Is there an element of cause and effect here? The shiver may well amplify the
effects and play a part in not allowing the rider to nullify the shimmy...
Another idea (I've never tested) - that shimmy was initially induced by the
front tyre being laterally unbalanced. At moderate to high speed this
imbalance would only need be very slight (ie, tyre slightly off-centre, not
manufactured with bonded tread absolutely central, carcass weighted to one
side, for example). Once a "quiver" has begun it might easily be amplified.
--
Alex Wheaton
Rick Onanian
<thalesN...@yahoo.com> wrote:
><jobst....@stanfordalumni.org> wrote in message
>> of normal human shivering, something that is related to the natural
>> response of the human muscles.
>
>Just because the shimmy frequency is close to the shiver frequency does not
>imply that shivering or other muscle instability causes a shimmy. I have
I think he didn't imply that. His message talked about the
similar frequency resulting in a feedback loop, whereby
the shimmy is allowed by muscles used to that motion,
and possibly even resulting in an addition to that motion
by stimulating the muscles. IIRC, IANAE, etc.
Or, put succinctly, he did not imply that muscle instability
causes shimmy; rather, he said that shimmy causes
muscle instability, which makes the original shimmy worse.
That all said, I have no experience with shimmy, and hope
never to have any; but if I do, I hope I will be sufficiently
educated from paying attention to these threads to do
something about it.
>Shayne Wissler
--
Rick "Bicycle hokey-pokey...that's what it's all about" Onanian
Werehatrack
have said:
>...bicycle shimmy is in the frequency
>of normal human shivering, something that is related to the natural
>response of the human muscles. Therefore, trying to resist shimmy by
>grabbing the bars firmly and attempting to counter the oscillation can
>easily lead to amplifying it. My early experience in this matter was
>that a friend could not get started on a cold morning before breakfast
>because he shimmied before the bicycle got moving and it only got
>worse from there.
>
>I believe that the terrified "death grip" is a major contributor to
>shimmy because the tense muscles naturally respond in the shimmy
>frequency. When I have ridden too far without food and a warm up in
>cold weather, I can detect the tendency to shimmy on descents and I
>take every precaution to not get caught in the feedback loop. This
>includes a loose grip on the bars.
One rider's perfect bike can be another's nightmare, as well; I've
seen shimmy only rarely (and haven't experienced it in a while), but
one memorable instance involved a road bike that shimmied horribly
under one particular rider, but not at all under me or the other three
who were present at the time.
The rider is part of the system; this is why from an engineering
standpoint, some of the possible problems may not be predictable.
Has anyone tried using a steering damper on a bicycle to combat this
problem? It's a ubiquitous solution on motorcycles.
David Mackintosh
> I think you missed the point that bicycle shimmy is in the frequency
> of normal human shivering, something that is related to the natural
> response of the human muscles. Therefore, trying to resist shimmy by
> grabbing the bars firmly and attempting to counter the oscillation can
> easily lead to amplifying it. My early experience in this matter was
> that a friend could not get started on a cold morning before breakfast
> because he shimmied before the bicycle got moving and it only got
> worse from there.
>
> I believe that the terrified "death grip" is a major contributor to
> shimmy because the tense muscles naturally respond in the shimmy
> frequency. When I have ridden too far without food and a warm up in
> cold weather, I can detect the tendency to shimmy on descents and I
> take every precaution to not get caught in the feedback loop. This
> includes a loose grip on the bars.
No, I agree with you on that point, and I do make an effort to keep a
loose grip whenever possible. What I need is a bike that doesn't tend
to shimmy at the "shiver" or muscle response frequency. I suspect
that the bike either needs to have a higher frequency (more stiffness
in lateral bending or torsion about the X-axis), more damping, or more
mass (obviously not desireable). I'd prefer not to accept that I
can't ride fast over bumpy pavement, brake into corners, ride hard in
cold weather, or that I'm just hosed if I hit a bump or bit of gravel
in mid-corner. Other friends (who almost all ride much smaller bikes)
seem to have much fewer problems. Occasionally they've had problems
when braking hard into a corner and being hit by a strong crosswind
gust, but only under fairly extreme conditions. It may also be a
problem with the larger (long-limbed) rider more than the larger bike,
hard to know.
-David
Shayne Wissler
"Rick Onanian" <spam...@cox.net> wrote in message
news:grjlnv8vforhf9bj6...@4ax.com...
> On Wed, 01 Oct 2003 05:38:54 GMT, "Shayne Wissler"
> <thalesN...@yahoo.com> wrote:
> ><jobst....@stanfordalumni.org> wrote in message
> >> I think you missed the point that bicycle shimmy is in the frequency
> >> of normal human shivering, something that is related to the natural
> >> response of the human muscles.
> >
> >Just because the shimmy frequency is close to the shiver frequency does
not
> >imply that shivering or other muscle instability causes a shimmy. I have
>
> I think he didn't imply that. His message talked about the
> similar frequency resulting in a feedback loop, whereby
> the shimmy is allowed by muscles used to that motion,
> and possibly even resulting in an addition to that motion
> by stimulating the muscles. IIRC, IANAE, etc.
This is (apparently) speculation on his part, and does not match my
experience.
> Or, put succinctly, he did not imply that muscle instability
> causes shimmy; rather, he said that shimmy causes
> muscle instability, which makes the original shimmy worse.
I'd like to know where he's getting his information. If it's from scientific
research and experiment, then I'd like to see the references. If it's just
his opinion it would be nice if he indicated that in his FAQ.
Shayne Wissler
Shayne Wissler
"Werehatrack" <rau...@earthWEEDSlink.net> wrote in message
> The rider is part of the system; this is why from an engineering
> standpoint, some of the possible problems may not be predictable.
If you never model the system, that's true. But if you model the bike and
the rider, you can change the parameters of the model involving the rider
and make such predictions. Perhaps all it would take is for a bike engineer
to meet up with a jet engineer (who deals with complicated problems like
this).
Shayne Wissler
Tom Nakashima
Next time you're on a high speed straight decent, grip the handlebars
tightly,
and wiggle it from side to side.
-tom
"Shayne Wissler" <thalesN...@yahoo.com> wrote in message
news:oQBeb.7070$%h1.5721@sccrnsc02...
Werehatrack
You think modeling the characteristics and interactional parameters of
a biological component are simple? Wanna buy a bridge?
Shayne Wissler
"Werehatrack" <rau...@earthWEEDSlink.net> wrote in message
> On Wed, 01 Oct 2003 14:52:49 GMT, "Shayne Wissler"
> <thalesN...@yahoo.com> may have said:
>
> >
> >"Werehatrack" <rau...@earthWEEDSlink.net> wrote in message
> >news:tiplnvo8g68j7h522...@4ax.com...
> >
> >> The rider is part of the system; this is why from an engineering
> >> standpoint, some of the possible problems may not be predictable.
> >
> >If you never model the system, that's true. But if you model the bike and
> >the rider, you can change the parameters of the model involving the rider
> >and make such predictions. Perhaps all it would take is for a bike
engineer
> >to meet up with a jet engineer (who deals with complicated problems like
> >this).
>
> You think modeling the characteristics and interactional parameters of
> a biological component are simple? Wanna buy a bridge?
Yeah, I think it's simple. That's why I said it required an engineer who
deals with complicated problems.
Obviously it's a more complicated problem than your average bicycle mechanic
is going to be able to figure out. What I want to know is whether or not
anyone with the required scientific background has even attempted to solve
the problem. These kinds of things are not unsolvable nowadays. Unless you
take the attitude that it's too hard, or that we should just live with it,
or that it's the bike rider's fault, and then don't even bother attempting
to solve it.
Shayne Wissler
Werehatrack
One of the problems is most certainly well understood; the effects of
low-amplitude resonant caster overcorrection are well documented in
research that goes back a long way. That's the easy part to
understand, and the often-noted similarities between bike designs in
the area of head angle and fork trail amounts owe much to the fact
that this *is* a well-understood phenomenon. What would have to be
added to that body of knowledge to answer *your* question is another
entire collection of empirical data that would be needed in order to
build the model of what's going on in *current* bikes, where light
weight, springy materials, and other design variations may have
introduced the possibility of other resonances as well.
Even once the data is in hand, though, that may not allow the
omniscient elimination of all resonances from any given frame.
Carmakers, who deal with this issue for every new vehicle design, have
found from long experience that you can't predict every resonance from
a model. Some, yes, but there are almost always others that won't be
caught. That's why they build prototypes, and then make design
corrections, and often end up adding resonant vibration dampers to the
vehicle somewhere. The tech for solutions in cars would probably not
help in bikes; if bike frame A was identified as having a potential
for a resonance with tire set X and rider Y and inflation Z, would the
rider accept the presence of a resonant damper (a lump of weight on an
elastomer spring, usually) as a solution? No way! The frame would
have to be modified, probably inducing a new set of resonances at some
other combination of loads and speeds...and that's just part of the
problem. With the current trends toward lighter bikes made from
thinner materials, I do not think that it may be possible to design
out every potential resonance for every likely rider...and the maker
that tries will probably find that the buyers are simply going over to
the brands where the costs are lower, since *most* of them will never
experience this problem in any event.
A bike manufacturer *could* throw enough money at the issue to find
out what causes it for a specific frame, but that neither guarantees
that a marketable solution exists, nor that it would provide a
competitive edge if it were discovered. Remember, many, if not most
riders will never experience the problem at all, and most won't care
about it as a result. For those that do experince the shimmy, it will
usually be infrequent, and solvable by farily trivial means. Trying
to throw big-tech solutions at it is, in my opinion, a sure way to go
broke.
Shayne Wissler
- Maybe the problem is coming from too many causes to analyze
- Maybe the solution would be too expensive/impractical
- Maybe it would cost too much to make it worth saving a few lives here and
there.
In other words, you haven't a clue. I can just as well answer:
- Maybe there are only a few causes or even one cause
- Maybe the solution would be cheap
- Maybe a few lives are worth spending the required R&D dollars.
What I can say for certain that it's a problem deserving of better treatment
than I've seen it get. A few hacks riding their bikes on the weekend and
experimenting with ways of dampening the vibration and then posting their
guesswork on the internet may be helpful, but it certainly isn't sufficient,
and doesn't substitute for some minimal attention to the problem on the part
of bicycle manufacturers.
Shayne Wissler
"Werehatrack" <rau...@earthWEEDSlink.net> wrote in message
news:127mnv4jfj9la0qji...@4ax.com...
Werehatrack
<thalesN...@yahoo.com> may have said:
>In essence you're saying:
> - Maybe the problem is coming from too many causes to analyze
> - Maybe the solution would be too expensive/impractical
> - Maybe it would cost too much to make it worth saving a few lives here and
>there.
>
>In other words, you haven't a clue. I can just as well answer:
> - Maybe there are only a few causes or even one cause
> - Maybe the solution would be cheap
> - Maybe a few lives are worth spending the required R&D dollars.
>
>What I can say for certain that it's a problem deserving of better treatment
>than I've seen it get. A few hacks riding their bikes on the weekend and
>experimenting with ways of dampening the vibration and then posting their
>guesswork on the internet may be helpful, but it certainly isn't sufficient,
>and doesn't substitute for some minimal attention to the problem on the part
>of bicycle manufacturers.
Then go get the funding to solve the problem. If you can't, consider
that there may be a reason.
Shayne Wissler
"Werehatrack" <rau...@earthWEEDSlink.net> wrote in message
> On Wed, 01 Oct 2003 19:39:52 GMT, "Shayne Wissler"
> <thalesN...@yahoo.com> may have said:
>
> >In essence you're saying:
> > - Maybe the problem is coming from too many causes to analyze
> > - Maybe the solution would be too expensive/impractical
> > - Maybe it would cost too much to make it worth saving a few lives here
and
> >there.
> >
> >In other words, you haven't a clue. I can just as well answer:
> > - Maybe there are only a few causes or even one cause
> > - Maybe the solution would be cheap
> > - Maybe a few lives are worth spending the required R&D dollars.
> >
> >What I can say for certain that it's a problem deserving of better
treatment
> >than I've seen it get. A few hacks riding their bikes on the weekend and
> >experimenting with ways of dampening the vibration and then posting their
> >guesswork on the internet may be helpful, but it certainly isn't
sufficient,
> >and doesn't substitute for some minimal attention to the problem on the
part
> >of bicycle manufacturers.
>
> Then go get the funding to solve the problem. If you can't, consider
> that there may be a reason.
"Maybe there's a reason that it's not worth funding research on this
problem".
Maybe God will reveal the solution to us in our dreams. Maybe a comet will
crash into the earth and we won't have to worry about bikes wobbling any
more. Maybe....
Why get out of bed in the morning? Maybe you'll miss an important call
saying that you won the lottery.
jobst....@stanfordalumni.org
>> I think you missed the point that bicycle shimmy is in the
>> frequency of normal human shivering, something that is related to
>> the natural response of the human muscles.
> Just because the shimmy frequency is close to the shiver frequency
> does not imply that shivering or other muscle instability causes a
> shimmy.
I didn't say that. What I said was that with a tense grip on the
handlebar any shimmy can be magnified and most likely not be
controlled by a person who is either trembling in fear or cold. The
hands-on shimmy is certainly such an event although few will recognize
that they admit to it by their description of their experience.
> I have descended this particular canyon many times, and this time
> was not particularly cold, nor was I nervous or particularly tired.
> The bike was definitely doing this vibrating on its own, though
> certainly my weight distribution at that particular speed could have
> been a factor. I was part of the system, but the instability was in
> the bike.
So to what do you attribute the change in response. The materials in
the bicycle do not change their response but the rider is a great
variable with the ability of denial of facts.
Jobst Brandt
jobst....@stanfordalumni.org
Rick Onanian
<thalesN...@yahoo.com> wrote:
>Why get out of bed in the morning? Maybe you'll miss an important call
>saying that you won the lottery.
Drat! I KNEW there was a reason I haven't yet won...it's because
I keep getting out of bed in the morning!
--
Rick "Won $100 once, though" Onanian
jobst....@stanfordalumni.org
> Remember, many, if not most riders will never experience the problem
> at all, and most won't care about it as a result. For those that do
> experince the shimmy, it will usually be infrequent, and solvable by
> farily trivial means. Trying to throw big-tech solutions at it is,
> in my opinion, a sure way to go broke.
We have seen shimmy in shopping carts as well as with older cars. The
first use of ball joint suspension (low friction) on VW (old beetle)
prototypes caused severe shimmy, after which the distance between the
joints was greatly enlarged to give high stiffness and move the
resonance out of the range that a wheel can follow. This is basically
what smaller bicycle frames do in that their shorter main tubes have
greater torsional stiffness causing a frequency mismatch between wheel
oscillation frequency and energy stored between bound and re-bound.
All fames that I have ridden were larger than 24" (crank CL to CL of
horizontal top tube measured along the seat tube) and all shimmied on
demand (no hands with pedals at top and bottom of stroke) at speeds
over 22mph. This has not interfered with years of bicycling, at any
speeds over all terrain. As I see it, the main problem lies in riders
who do not understand what reinforces the phenomenon and whether their
bicycles are prone to that response in the first place.
Crashing as a result of this is much like diving from the bicycle when
the chain skips. This is not an unmanageable phenomenon.
Jobst Brandt
jobst....@stanfordalumni.org
Shayne Wissler
<jobst....@stanfordalumni.org> wrote in message
news:KzGeb.26575$dk4.8...@typhoon.sonic.net...
> Shayne Wissler writes:
>
> >> I think you missed the point that bicycle shimmy is in the
> >> frequency of normal human shivering, something that is related to
> >> the natural response of the human muscles.
>
> > Just because the shimmy frequency is close to the shiver frequency
> > does not imply that shivering or other muscle instability causes a
> > shimmy.
>
> I didn't say that. What I said was that with a tense grip on the
> handlebar any shimmy can be magnified and most likely not be
> controlled by a person who is either trembling in fear or cold. The
> hands-on shimmy is certainly such an event although few will recognize
> that they admit to it by their description of their experience.
You speak as if you have a scientific certainty here. Is this merely
posturing, or do you have some scientific analysis to add?
> > I have descended this particular canyon many times, and this time
> > was not particularly cold, nor was I nervous or particularly tired.
> > The bike was definitely doing this vibrating on its own, though
> > certainly my weight distribution at that particular speed could have
> > been a factor. I was part of the system, but the instability was in
> > the bike.
>
> So to what do you attribute the change in response. The materials in
> the bicycle do not change their response but the rider is a great
> variable with the ability of denial of facts.
You have an average ability in ad hominems. Perhaps that works with most
people you encounter. It doesn't work on me. You know, I can do ad hominems
too, and I think I do a better job of it when I want to. For example, what
possible motivation might you have for wanting to blame the rider at every
turn? Let's see, could it be the fact that bicycle manufacturers pay you
money to testify against injured cyclists?
But let's get back on subject. I only ask you to refrain from the ad
hominems and just present whatever scientific knowledge you might have. If
you have none then feel free to take your ad hominems somewhere else--I'm
not interested in your speculations about what cyclist might have been
shivering from what, or your psychologizing about who might be in denial of
what facts.
The Tacoma Narrows Bridge is an apt example here. The bridge worked fine in
many circumstances. But there was one particular circumstance where it
failed. That was enough to call the bridge a complete engineering failure.
Civil engineers used it to learn from past mistakes and not make them again.
A bike that works for most riders, or for most weight distributions, or for
most handlebar positions, etc., but has a drastic and unpredictable failure
mode at a particular speed etc., represents a similar design failure. Yes
the bicycle's materials don't change. Neither did the bridge's materials.
But the conditions of the uses *do* change. And when those conditions are in
the realm of what the designer should expect, and the bike does something
radically wrong, there's something wrong with the bike. You can't blame the
rider because he leans forward a little, or tightens his grip, and the bike
starts to radically vibrate. It may be good advice to recommend that, for a
vibrating bike, the cyclist do various things to accomodate, but this is in
order to compensate for defective behavior, not something that the rider
"should" have been doing all along.
Shayne Wissler
Tom Paterson
>Yes
>the bicycle's materials don't change.
How about the pressure in the tires? The only time I ever had a bad speed
wobble was trying to get stopped after running over a thumbtack on a Rockies
descent (Rt. 82 to Difficult Campground outside Aspen, probably about the usual
7% for Co. grades). Rode the same bike/tires/etc. "many" times down that hill
with no problem as long as the tires were pumped up. Braking with a deflating
front was quite different. --TP
Shayne Wissler
"Tom Paterson" <dusto...@aol.comnospam> wrote in message
news:20031001165700...@mb-m20.aol.com...
Good point. And then there's the change of the constant wear on the tires.
Of course your particular change in materials would be expected to lead to a
bad result.
In my case there was a change in materials too, that one would *not*
reasonably expect to lead to a failure mode: I changed the handlebar height
(within manufacturer spec), and replaced the front tire. I don't know for
sure whether either of these were the cause, but they are suspicious since
they were recent changes (last 30-60 days).
Shayne Wissler
jobst....@stanfordalumni.org
>> So to what do you attribute the change in response. The materials in
>> the bicycle do not change their response but the rider is a great
>> variable with the ability of denial of facts.
> You have an average ability in ad hominems. Perhaps that works with
> most people you encounter. It doesn't work on me. You know, I can
> do ad hominems too, and I think I do a better job of it when I want
> to. For example, what possible motivation might you have for
> wanting to blame the rider at every turn? Let's see, could it be
> the fact that bicycle manufacturers pay you money to testify against
> injured cyclists?
Interesting twist. Where do you get that notion? You might want to
cite such a case if you want to improve your credibility.
Nice dodge. So to what do you attribute the change in response,
considering that according to your recounting of the event, everything
was the same. You seem to want others to solve your problem.
> But let's get back on subject. I only ask you to refrain from the ad
> hominems and just present whatever scientific knowledge you might
> have. If you have none then feel free to take your ad hominems
> somewhere else--I'm not interested in your speculations about what
> cyclist might have been shivering from what, or your psychologizing
> about who might be in denial of what facts.
These considerations come from observed phenomena of riders who had
exactly these problems. You don't address why you believe these
assessments are invalid or not scientific. How about putting forth
some of your own ideas on the subject instead of attacking those that
have been proposed.
Some of my findings arise from the time that I designed automotive
suspension for racing and sports cars at Porsche, analyzing their
response and that of motorcycles and bicycles that have some common
problems such as shimmy.
> The Tacoma Narrows Bridge is an apt example here. The bridge worked
> fine in many circumstances. But there was one particular
> circumstance where it failed. That was enough to call the bridge a
> complete engineering failure. Civil engineers used it to learn from
> past mistakes and not make them again.
Unlike your bicycle, the conditions were different. This was the
first time the bridge was subjected to a continuous wind of that
magnitude. Once it began to twist from lateral sway, it became an
oscillating air foil with angular pitch. This bridge has been dragged
into proofs of many unrelated phenomena by armchair experts. It does
not apply here.
> A bike that works for most riders, or for most weight distributions,
> or for most handlebar positions, etc., but has a drastic and
> unpredictable failure mode at a particular speed etc., represents a
> similar design failure.
> Yes the bicycle's materials don't change. Neither did the bridge's
> materials. But the conditions of the uses *do* change. And when
> those conditions are in the realm of what the designer should
> expect, and the bike does something radically wrong, there's
> something wrong with the bike. You can't blame the rider because he
> leans forward a little, or tightens his grip, and the bike starts to
> radically vibrate. It may be good advice to recommend that, for a
> vibrating bike, the cyclist do various things to accomodate, but
> this is in order to compensate for defective behavior, not something
> that the rider "should" have been doing all along.
I think Sheldon Browns item on left hand threads has some appropriate
words on this:
# Ignorant people outside the bike industry sometimes make the
# astonishing discovery that the way it has been done for 100 years is
# "wrong." "Look at these fools, they go to the trouble of using a
# left thread on one pedal, then the bozos go and put the left thread
# on the wrong side! Shows that bicycle designers have no idea what
# they are doing..."
Steering dampers and other anti shimmy devices have not found favor
among bicyclists because the problem is neither serious enough nor the
mechanisms an acceptable alternative in cost, weight, or convenience.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
That may be so, but we aren't talking about a flat tire here. Besides,
you didn't say whether your bicycle began to shimmy. I can imagine a
hissing leak can cause some consternation on a fast descent.
Jobst Brandt
jobst....@stanfordalumni.org
Werehatrack
have said:
>Werehatrack who? writes:
>
>> Remember, many, if not most riders will never experience the problem
>> at all, and most won't care about it as a result. For those that do
>> experince the shimmy, it will usually be infrequent, and solvable by
>> farily trivial means. Trying to throw big-tech solutions at it is,
>> in my opinion, a sure way to go broke.
>
>We have seen shimmy in shopping carts as well as with older cars. The
>first use of ball joint suspension (low friction) on VW (old beetle)
>prototypes caused severe shimmy, after which the distance between the
>joints was greatly enlarged to give high stiffness and move the
>resonance out of the range that a wheel can follow.
The VW rear-drive vehicles were all susceptible to resonant shimmy,
and by 1961 they all had steering dampers, even the model 181 which
had a modified Type 1 front axle with wider joint spacing than the
Beetle. See below for more info.
>This is basically
>what smaller bicycle frames do in that their shorter main tubes have
>greater torsional stiffness causing a frequency mismatch between wheel
>oscillation frequency and energy stored between bound and re-bound.
Yes, that's the problem, in a nutshell.
By the way, in the VW, the steering damper became standard equipment
in 1958 (or thereabouts; it might have been a year or two either way)
while the front ends were still equipped with kingpins, and after the
design went to ball joints in 1966, the spacing of the joints never
changed. The diameter of the ball joint stems was changed once, but a
VW Beetle front end with ball joints of any year will shimmy violently
if the damper is bad or missing. Kingpin front ends had the problem
to a slightly lesser extent, but it was still serious enough to merit
the damper. When the damper was first introduced as factory standard
equipment, it was also made available as a retrofit kit for all prior
models due to customer complaints about the problem. The MacPherson
strut suspensions on the Super Beetles were not immune; they, too, had
(and needed) a damper. (I was a VW dealer parts manager from 1981 to
1985, and had been in the VW parts business since 1973.)
>All fames that I have ridden were larger than 24" (crank CL to CL of
>horizontal top tube measured along the seat tube) and all shimmied on
>demand (no hands with pedals at top and bottom of stroke) at speeds
>over 22mph. This has not interfered with years of bicycling, at any
>speeds over all terrain. As I see it, the main problem lies in riders
>who do not understand what reinforces the phenomenon and whether their
>bicycles are prone to that response in the first place.
I quite agree, although since I've experienced the problem far less,
it's much easier for me to ignore. At high speeds, I simply don't
take both hands off the bars, so I guess my habits have shielded me
from having to deal with the effects.
>Crashing as a result of this is much like diving from the bicycle when
>the chain skips. This is not an unmanageable phenomenon.
Unwanted, but as you say, not unmanageable.
Werehatrack
may have said:
>On Wed, 01 Oct 2003 20:10:40 GMT, "Shayne Wissler"
><thalesN...@yahoo.com> wrote:
>>Why get out of bed in the morning? Maybe you'll miss an important call
>>saying that you won the lottery.
>
>Drat! I KNEW there was a reason I haven't yet won...it's because
>I keep getting out of bed in the morning!
Dontcha just love people who scream "There's a problem here, and
somebody needs to fix it!", but who get all huffy when the answer is,
"Okay, go ahead."
Werehatrack
have said:
>Steering dampers and other anti shimmy devices have not found favor
>among bicyclists because the problem is neither serious enough nor the
>mechanisms an acceptable alternative in cost, weight, or convenience.
That's pretty much what I had suspected. (I had tried, as a mental
exercise, to come up with a clean way to retrofit one, and nothing I
could think of was without drawbacks that I found unacceptable.
Possible, yes, certainly; worth the effort and side effects, no, I
don't think so.)
Werehatrack
<rau...@earthWEEDSlink.net> may have said:
>The VW rear-drive vehicles were all susceptible to resonant shimmy,
>and by 1961 they all had steering dampers, even the model 181 which
>had a modified Type 1 front axle with wider joint spacing than the
>Beetle. See below for more info.
Of course, the model 181 didn't go into production until 1972 IIRC,
but it had a damper, and it needed one.
Brian Smith
in response to:
> > It appears that there must be a substantial number of variables that
> > can, individually or in combination, have an effect on the presence
> > and severity of the problem...but it does not appear that there is any
> > established methodology for evaluating the possible factors and
> > identifying the cause in any given case, beyond the "try this stuff
> > and see what works" approach.
"Shayne Wissler" <thalesN...@yahoo.com> wrote in message
news:phteb.641533$YN5.493906@sccrnsc01...
>
> Well this just won't do. We live in a day and age where science and
> technology can answer such questions--assuming the interested parties take
> interest. Maybe back in the 60's such a stance made sense, but we've got
all
> sorts of fancy methods and tools for dealing with these kinds of problems.
> How many physics PhD's have looked into this issue? What tests have been
> run? Has there been any scientific approach at all to this issue, or is it
> only individual cyclists that have built up an unscientific lore about the
> shimmy?
>
> I would assume that companies like Trek would care about whether their
> products were safe, and put at least some R&D into this issue. Indeed, it
> seems like a good opportunity to make some extra cash: if they figure out
> the problem, and keep the answer proprietary, they can offer bikes that
are
> guaranteed not to wobble. In any case, it doesn't help business to have
some
> people scared out of the sport, or worse. And it doesn't help for cyclists
> to take a passive stand on the issue and just accept wobbling bikes.
>
If a company spent money to have, as you suggest, Physics PhDs look into the
issue of shimmying bikes, do you think they would have people trolling this
group
to let us know for free what they have found out? Why wouldn't they just
produce shimmy-free bikes and not advertise that fact? Surely the number of
cyclists who have experienced shimmy and are in the market for another bike
are
a vast minority of bike shoppers. Bike consumers seem to be swayed much
more
convincingly by the visual identifiers of technical advancements than a
scientific claim
substantiated only by a guarantee.
I think that most companies of significant size have faced the shimmy issue
at one point
or another, but that it hasn't been worth the trouble to understand the
underlying cause,
since the problem bikes aren't terribly common, are less commonly exposed as
such by
their riders, and for those that do and have their cases examined, some
component change
or slew of changes typically solves the problem without needing to
understand it.
I'd very much, as I'm sure many of us would, like to know the underlying
cause well enough
to successfully predict it.
In similarity to your idea of the value in the marketplace of guarantees of
non-shimmy design,
an indivicual who did understand it completely could market their knowledge
to
manufacturers so that the manufacturers could design problem shimmy out of
their bikes.
It seems that we the interested see as much likely fruit of this labor as do
the manufacturers
to do it themselves.
There is good info in the Faq on this, there is a lot of noise and some
additional interesting
ideas in the archives of this group, and I suspect that's close to the best
anyone has done.
-Brian Smith in NY
jim beam
>>what smaller bicycle frames do in that their shorter main tubes have
>>greater torsional stiffness causing a frequency mismatch between wheel
>>oscillation frequency and energy stored between bound and re-bound.
> Yes, that's the problem, in a nutshell.
yep. "tuning".
Shayne Wissler
<jobst....@stanfordalumni.org> wrote in message
news:lNHeb.26592$dk4.8...@typhoon.sonic.net...
> Shayne Wissler writes:
>
> >> So to what do you attribute the change in response. The materials in
> >> the bicycle do not change their response but the rider is a great
> >> variable with the ability of denial of facts.
>
> > You have an average ability in ad hominems. Perhaps that works with
> > most people you encounter. It doesn't work on me. You know, I can
> > do ad hominems too, and I think I do a better job of it when I want
> > to. For example, what possible motivation might you have for
> > wanting to blame the rider at every turn? Let's see, could it be
> > the fact that bicycle manufacturers pay you money to testify against
> > injured cyclists?
>
> Interesting twist. Where do you get that notion? You might want to
> cite such a case if you want to improve your credibility.
It's not an allegation. Just an educated guess. Not unlike your ad hominems,
except perhaps that mine have more basis in fact. Perhaps if you provide
evidence for your wild assumptions about what psychological reasons caused
my shimmy, I'll provide reasons why I'd guess that you might represent
bicycle companies. But really my motive here was to attempt to get you to
cease and desist with your invalid argumentative techniques.
> Nice dodge. So to what do you attribute the change in response,
> considering that according to your recounting of the event, everything
> was the same.
No, you're the one dodging. I answered your question.
> You seem to want others to solve your problem.
You seem to want to pretend to provide answers. I'm just trying to keep the
answers honest.
> > But let's get back on subject. I only ask you to refrain from the ad
> > hominems and just present whatever scientific knowledge you might
> > have. If you have none then feel free to take your ad hominems
> > somewhere else--I'm not interested in your speculations about what
> > cyclist might have been shivering from what, or your psychologizing
> > about who might be in denial of what facts.
>
> These considerations come from observed phenomena of riders who had
> exactly these problems.
So, since rider X got scared out of his wits while shimmying, rider Y must
have been too.
> You don't address why you believe these
> assessments are invalid or not scientific.
Well it's pretty obvious what's wrong with the reasoning. Just because
people have the capacity to be scared, deluded, or to lie, does not imply
that a particular person is scared, deluded, or lying. As a matter of fact I
was not scared at all, and I am presenting the facts to the best of my
recollection. You can even see my polar data to see my speed just before a
rapid deceleration, with only a slight rise in heart rate, which I attribute
to the increase in the physical demands of stopping since I was not scared.
> How about putting forth
> some of your own ideas on the subject instead of attacking those that
> have been proposed.
I did put forth a technical hypothesis actually. I also like your shopping
cart example. It's a good start.
> Some of my findings arise from the time that I designed automotive
> suspension for racing and sports cars at Porsche, analyzing their
> response and that of motorcycles and bicycles that have some common
> problems such as shimmy.
Technical credentials are good, but they aren't a substitute for a causal
explanation. And I realize that you owe no one a causal explanation.
> > The Tacoma Narrows Bridge is an apt example here. The bridge worked
> > fine in many circumstances. But there was one particular
> > circumstance where it failed. That was enough to call the bridge a
> > complete engineering failure. Civil engineers used it to learn from
> > past mistakes and not make them again.
>
> Unlike your bicycle, the conditions were different. This was the
> first time the bridge was subjected to a continuous wind of that
> magnitude. Once it began to twist from lateral sway, it became an
> oscillating air foil with angular pitch. This bridge has been dragged
> into proofs of many unrelated phenomena by armchair experts. It does
> not apply here.
The bridge is perfectly apt as I have demonstrated, and since nothing in the
above addresses the subject of whether it's actually apt, nor anything I
actually said, I see no reason to say anything, except to observe yet
another mediocre attempt at an ad hominem argument. Apparently the fact that
you worked for Porche is supposed to make us overlook the fact that your
main method of presenting conclusions is to insult those who disagree with
you.
> > A bike that works for most riders, or for most weight distributions,
> > or for most handlebar positions, etc., but has a drastic and
> > unpredictable failure mode at a particular speed etc., represents a
> > similar design failure.
>
> > Yes the bicycle's materials don't change. Neither did the bridge's
> > materials. But the conditions of the uses *do* change. And when
> > those conditions are in the realm of what the designer should
> > expect, and the bike does something radically wrong, there's
> > something wrong with the bike. You can't blame the rider because he
> > leans forward a little, or tightens his grip, and the bike starts to
> > radically vibrate. It may be good advice to recommend that, for a
> > vibrating bike, the cyclist do various things to accomodate, but
> > this is in order to compensate for defective behavior, not something
> > that the rider "should" have been doing all along.
>
> I think Sheldon Browns item on left hand threads has some appropriate
> words on this:
>
> # Ignorant people outside the bike industry sometimes make the
> # astonishing discovery that the way it has been done for 100 years is
> # "wrong." "Look at these fools, they go to the trouble of using a
> # left thread on one pedal, then the bozos go and put the left thread
> # on the wrong side! Shows that bicycle designers have no idea what
> # they are doing..."
Another ad hominem. You're really starting to bore me with this.
> Steering dampers and other anti shimmy devices have not found favor
> among bicyclists because the problem is neither serious enough nor the
> mechanisms an acceptable alternative in cost, weight, or convenience.
IF you had provided any evidence that those are the only alternatives, then
perhaps I would be sympathetic to your points. But obviously, many bikes
don't shimmy at cycling speeds--without the aid of these devices. So there
is reason to believe that a more elegant solution to the shimmy problem is
possible. And that's really my main complaint here. You seem think that the
only alternative is some kind of clumbsy contraption, that a clever idea
isn't going to solve the problem. And in your expert status you foster an
anti-investigation attitude. Well if you have absolute proof, then fine, we
shouldn't waste our time. But history is riddled with "experts" who held a
field back because of their dogma.
Shayne Wissler
Shayne Wissler
"Werehatrack" <rau...@earthWEEDSlink.net> wrote in message
> On Wed, 01 Oct 2003 16:28:14 -0400, Rick Onanian <spam...@cox.net>
> may have said:
>
> >On Wed, 01 Oct 2003 20:10:40 GMT, "Shayne Wissler"
> ><thalesN...@yahoo.com> wrote:
> >>Why get out of bed in the morning? Maybe you'll miss an important call
> >>saying that you won the lottery.
> >
> >Drat! I KNEW there was a reason I haven't yet won...it's because
> >I keep getting out of bed in the morning!
>
> Dontcha just love people who scream "There's a problem here, and
> somebody needs to fix it!", but who get all huffy when the answer is,
> "Okay, go ahead."
I never demanded that anyone fix the problem.
My problem is with those who claim it isn't a problem with the bike, and/or
who say that if it is a problem with the bike then it's intractable and so
the best we can do is work around the problem. If that's their position then
I expect proof of this intractability.
Shayne Wissler
David Mackintosh
> On Wed, 01 Oct 2003 21:36:17 GMT, jobst....@stanfordalumni.org may
> have said:
>
> >Steering dampers and other anti shimmy devices have not found favor
> >among bicyclists because the problem is neither serious enough nor the
> >mechanisms an acceptable alternative in cost, weight, or convenience.
>
> That's pretty much what I had suspected. (I had tried, as a mental
> exercise, to come up with a clean way to retrofit one, and nothing I
> could think of was without drawbacks that I found unacceptable.
> Possible, yes, certainly; worth the effort and side effects, no, I
> don't think so.)
There is a steering damper made for bicycles available:
http://store.hopey.org/
I have no experience with it, haven't even seen one. A linear damper
mounted between the triple-clamp or a fork tube and frame is often
used on motorcycles, something similar could be used between the fork
crown and down tube on a bicycle. Another much simpler and possibly
just as effective solution would be bar-end weights, also common on
motorcycles. Although I find the problem to be quite serious, and
have gone to considerable expense to find a racing-type bike that
doesn't deathwobble (unsuccessfully, so far), I don't think adding
mass or a damper should be necessary. Admittedly, I'm unusually
proportioned (over 38" inseam, but only 6'3"), which may be part of
the reason why I seem to have more difficulty with this issue than
most.
-David
Werehatrack
Mackintosh) may have said:
The damper would probably be effective, in my opinion.
From what Jobst Brandt was saying elsewhere in the thread, this type
of problem is likely to be hard to completely defeat with a large
frame. I'm wondering if a compact frame with a longer seatpost, like
many of the hybrids, might not be less prone to the resonances.
anerobic
lowered my handlebars by about 2". They used to be almost parallel to my
seat.<<<< I did tighten the headset well.>>> The other is that I
replaced my front tire with a lighter, skinnier one.
i have had this type of wobble once on an aluminum bike, reproducibly,
and it went away by tightening the headset, which was a little loose.
you might check to make sure....
--
>--------------------------<
Posted via cyclingforums.com
http://www.cyclingforums.com
Tom Nakashima
from Cambria
to Paso Robles on Hwy 46. I've been riding this route every year for the
last 7 years when
I attend the Great Western Bike Rally. Every time I get to this fast
descending area of my return route, I'm caution to see if my bike will
shimmy again. I've been riding the same road bike (steel frame) with the
same components, including handlebars, and the same type of tires, Mavic
MA-2 rims with Avocet Road 28's, which are now the Road 25's, and the same
tire pressure of 100psi. but haven't been able to duplicate the shimmy
traveling at the
approximately the same speed of 42-45mph on the descent. I believe as Mr.
Brandt says; it sounds like I may have been a little fatigued from riding
all day and could have involuntary induced the wobble myself. That was the
only time I've experienced shimmy with my road-bike.
-tom
"anerobic" <usenet...@cyclingforums.com> wrote in message
news:3f7bb4ef$1...@news.chariot.net.au...
David Mackintosh
> The damper would probably be effective, in my opinion.
>
> From what Jobst Brandt was saying elsewhere in the thread, this type
> of problem is likely to be hard to completely defeat with a large
> frame. I'm wondering if a compact frame with a longer seatpost, like
> many of the hybrids, might not be less prone to the resonances.
That'll be my next try, a custom steel frame with a sloping, large
diameter (probably 1-3/8") top tube. Also slightly slacker head angle
and longer chainstays than typical for a large road frame to lengthen
the wheelbase (but the top tube will be fairly short).
-David
jobst....@stanfordalumni.org
> I've been riding the same road bike (steel frame) with the same
> components, including handlebars, and the same type of tires, Mavic
> MA-2 rims with Avocet Road 28's, which are now the Road 25's, and
> the same tire pressure of 100psi. but haven't been able to
> duplicate the shimmy traveling at approximately the same speed of
> 42-45mph on the descent.
There is an excellent test course for this near your work place on
Sand Hill road. Ride to the top of Sand Hill and coast eastward
toward the freeway no-hands with pedals vertical, knees not touching
the top tube. I don't think speeds over 30 are needed for shimmy on a
bicycle. If your bicycle shimmies naturally, it will do it on this
road. If it doesn't, then your shimmy must have been rider induced.
Jobst Brandt
jobst....@stanfordalumni.org
Tom Nakashima
I've ridden the east slopes of Sand Hill Rd. many times during lunch and
after work and never got my
road-bike to shimmy there, not that I've really tried either. I do however
find this high-speed instability/wobble/shimmy interesting. I believe this
is one of the few mysteries in cycling that hasn't been
solved. A friend of mine thinks it's the design of the bike, but I disagree.
I still think it's self induced and going to experiment more on this. I'm
thinking it has to do with gripping the handlebars and creating a resonance,
then amplifying the amplitude of oscillation by resistance. I've also
experimented with riding with one hand on the bar with my upright handlebar
bike, which I have been able to induce the shimmy even on a straightaway.
Some only think that shimmy only occurs on a descent.
Pretty fascinating. I remember you once said that everything in cycling has
just about been done, and redone.
Let me know if you have more theories or suggestions on this matter, since
they're easy to try.
-tom
<jobst....@stanfordalumni.org> wrote in message
news:yj_eb.26864$dk4.8...@typhoon.sonic.net...
jobst....@stanfordalumni.org
>>> I've been riding the same road bike (steel frame) with the same
>>> components, including handlebars, and the same type of tires,
>>> Mavic MA-2 rims with Avocet Road 28's, which are now the Road
>>> 25's, and the same tire pressure of 100psi. but haven't been able
>>> to duplicate the shimmy traveling at approximately the same speed
>>> of 42-45mph on the descent.
>> There is an excellent test course for this near your work place on
>> Sand Hill road. Ride to the top of Sand Hill and coast eastward
>> toward the freeway no-hands with pedals vertical, knees not
>> touching the top tube. I don't think speeds over 30 are needed for
>> shimmy on a bicycle. If your bicycle shimmies naturally, it will
>> do it on this road. If it doesn't, then your shimmy must have been
>> rider induced.
> I've ridden the east slopes of Sand Hill Rd. many times during lunch
> and after work and never got my road-bike to shimmy there, not that
> I've really tried either. I do however find this high-speed
> instability/wobble/shimmy interesting. I believe this is one of the
> few mysteries in cycling that hasn't been solved. A friend of mine
> thinks it's the design of the bike, but I disagree. I still think
> it's self induced and going to experiment more on this. I'm
> thinking it has to do with gripping the handlebars and creating a
> resonance, then amplifying the amplitude of oscillation by
> resistance. I've also experimented with riding with one hand on the
> bar with my upright handlebar bike, which I have been able to induce
> the shimmy even on a straightaway. Some only think that shimmy only
> occurs on a descent. Pretty fascinating. I remember you once said
> that everything in cycling has just about been done, and redone.
> Let me know if you have more theories or suggestions on this matter,
> since they're easy to try.
I didn't see that you tried the test I suggested. Shimmy only occurs
on conventional bicycles either when rider induced or while riding
no-hands. You must ride no-hands to perform the "does this bicycle
shimmy" test. Until you do this you will not get closer to the source
of your shimmy experience. The course I suggested is my standard one
for such tests because the grade is uniform, the road smooth and it
has no traffic problems with its wide and integral bicycle lanes.
Jobst Brandt
jobst....@stanfordalumni.org
Shayne Wissler
> Shimmy only occurs
> on conventional bicycles either when rider induced or while riding
> no-hands.
I keep seeing you repeat this but I have never seen you substantiate it. And
it flies in the face of my experience.
And these aren't even two different categories. Riding no-hands qualifies
more as a rider-induced shimmy than does riding with your hands on the
handlebars. So in your world-view, all shimmies are rider induced:
1. Rider induces purposefully by removing hands
2. Rider induces purposefully by some hands-on technique
3. Rider induces inadvertently through fear or shivering or something.
Your position, stated in honest terms, is that "Shimmy only occurs on
conventional bicycles when rider induced." Your view is that the rider is
*always* the cause. Presumably failing to put ones knees against the top
tube is "causing" the bike to shimmy?
The truth of the matter is that shimmy is coming from some *undesirable*,
unpredictable harmonic oscillation. Bikes are not designed to shimmy; they
shimmy due to factors that are apparently beyond current design practices
to overcome without making undue compromises. I.e., the only way they know
how to fix the problem is to fiddle with components or hack the design by
adding dampeners.
The true cause is the complete system of bike and rider, *but the bicycle
designer's job is to account for the full range of reasonable rider
variations*. If the designer knows that some riders will be 150lbs, some
will be 220lbs, then the frame must withstand that range of weights. If he
knows that the rider may sit straight up, or lean almost over the
handlebars, then he must account for that. Likewise he must account for
various grips on the handlebars.
Perhaps what you mean to say, is that given the current state of the art, it
is the rider's *responsibility*, for the sake of his own safety, to be able
to respond correctly to shimmy. I agree with that. But saying it that way
instead of the way you put it leaves room for designers to have a healthy
frustration over the issue and not be complacent about it. It leaves room
for a clever engineer with his sights set on the problem to solve it
elegantly.
As an expert you should be doing what you can to encourage these kinds of
improvements, not providing rationalizations for the evasion of a definite
design problem.
Shayne Wissler
Dick Schoeller
resonant feedback that you often won't notice it when your hands on the
bars. They provide enough bracing to kill the vibrations. When you take
your hands off the bars, the system is free to vibrate and you get the
shimmy.
--
Dick Schoeller
mailto:scho...@comcast.net
http://schoeller.ne.client2.attbi.com/
781.449.5476
"Er ist ein Narr, der meint, es sei nicht schad, das Kind
auszuschütten mit dem Bad" - Thomas Murner 1512
jobst....@stanfordalumni.org
>> Shimmy only occurs on conventional bicycles either when rider
>> induced or while riding no-hands.
> I keep seeing you repeat this but I have never seen you substantiate
> it. And it flies in the face of my experience.
You are ignoring the examples I cite and the tests that I have done,
changing the weight and inflation pressure of the wheel, balancing and
unbalancing the wheel and riding over test courses to find what
interferes with shimmy buildup. All my road bicycles that I have
owned shimmied when allowed to do so by riding no-hands at the suitable
speed.
> And these aren't even two different categories. Riding no-hands
> qualifies more as a rider-induced shimmy than does riding with your
> hands on the handlebars. So in your world-view, all shimmies are
> rider induced:
> 1. Rider induces purposefully by removing hands
> 2. Rider induces purposefully by some hands-on technique
> 3. Rider induces inadvertently through fear or shivering or something.
That may be your interpretation, but riding no-hands is part of
bicycling, especially competitive bicycling where riders sit up to eat
and drink or change shirts while traveling at speeds that can induce
shimmy if allowed to occur. The constraint of always keeping hands on
the bars is unacceptable.
> Your position, stated in honest terms, is that "Shimmy only occurs
> on conventional bicycles when rider induced." Your view is that the
> rider is *always* the cause. Presumably failing to put ones knees
> against the top tube is "causing" the bike to shimmy?
That's your interpretation. When a coasting bicycle, with no rider
input, begins to shimmy is not rider induced in my perception. Rider
induced is when a rider has his hands on the bars and the bicycle
begins to shimmy. With the damping of hands and arms on the bars,
shimmy must be induced by an input from the rider. I have explained
how that occurs.
> The truth of the matter is that shimmy is coming from some
> *undesirable*, unpredictable harmonic oscillation. Bikes are not
> designed to shimmy; they shimmy due to factors that are apparently
> beyond current design practices to overcome without making undue
> compromises. I.e., the only way they know how to fix the problem is
> to fiddle with components or hack the design by adding dampeners.
As you may have noticed, it is not a serious problem and I have not
heard any people with whom I ride complain about it interfering with
their riding, safety or convenience. There are plenty of tall racers
whose bicycles will shimmy if given the opportunity. They never even
mention it. I have such a bicycle that will shimmy and can test
wheels whose makers claim they are shimmy resistant and show that they
are mistaken. My current bicycle has carried me over more than
200,000 miles on all sorts of roads and trails at speeds over 100km/h
without incident. It is NOT a problem.
> The true cause is the complete system of bike and rider, *but the
> bicycle designer's job is to account for the full range of
> reasonable rider variations*. If the designer knows that some
> riders will be 150lbs, some will be 220lbs, then the frame must
> withstand that range of weights. If he knows that the rider may sit
> straight up, or lean almost over the handlebars, then he must
> account for that. Likewise he must account for various grips on the
> handlebars.
I take it you want to write specifications for bicycle safety on
shimmy that you state you do not understand. I don't think that would
be a good project. On the other hand, when does your bicycle shimmy
and what have you done to understand it?
> Perhaps what you mean to say, is that given the current state of the
> art, it is the rider's *responsibility*, for the sake of his own
> safety, to be able to respond correctly to shimmy. I agree with
> that. But saying it that way instead of the way you put it leaves
> room for designers to have a healthy frustration over the issue and
> not be complacent about it. It leaves room for a clever engineer
> with his sights set on the problem to solve it elegantly.
Do it!
> As an expert you should be doing what you can to encourage these
> kinds of improvements, not providing rationalizations for the
> evasion of a definite design problem.
It's called "this kind of thing" or "these things", not both.
I'm waiting for someone, with better insights than I, to solve this.
From motor vehicles I see that they do not have a solution other than
steering dampers. With motor power, such devices are bearable. It's
so old that before I rode a motorcycle I heard of "tank slappers" and
"sun-fishing".
Jobst Brandt
jobst....@stanfordalumni.org
Shayne Wissler
> I would read Jobst's post to mean that if you have a shimmy caused by
> resonant feedback that you often won't notice it when your hands on the
> bars. They provide enough bracing to kill the vibrations. When you take
> your hands off the bars, the system is free to vibrate and you get the
> shimmy.
Well then there's a gross misunderstanding here on his part. That shimmies
of the character you refer to occur I have no doubt, but the type of shimmy
I experienced was violent. The front end of the bike jerked my hands back
and forth.
Since Brandt is stuck in his own dogmatic interpretations of shimmy based on
his own hacking around on a few bicycles, I know he's just going to say
that this doesn't happen unless the rider is somehow inducing it, but so
far he has presented no scientific basis for his position.
Shayne Wissler
jim beam
> heard any people with whom I ride complain about it interfering with
> their riding, safety or convenience. There are plenty of tall racers
> whose bicycles will shimmy if given the opportunity. They never even
> mention it. I have such a bicycle that will shimmy and can test
> wheels whose makers claim they are shimmy resistant and show that they
> are mistaken. My current bicycle has carried me over more than
> 200,000 miles on all sorts of roads and trails at speeds over 100km/h
> without incident. It is NOT a problem.
nothing personal jobst, but i have to strongly disagree with you here.
my old 63cm frame shimmied so bad, it threw me and i broke a hip. i
don't call 8 weeks on crutches and 12 months of pain "not a problem".
i still have and still ride those wheels, and they /don't/ shimmy with
any of my new frames.
please mark me down as someone that /has/ mentioned it.
jb
Shayne Wissler
> Shayne Wissler writes:
>
>>> Shimmy only occurs on conventional bicycles either when rider
>>> induced or while riding no-hands.
>
>> I keep seeing you repeat this but I have never seen you substantiate
>> it. And it flies in the face of my experience.
>
> You are ignoring the examples I cite and the tests that I have done,
No, I'm just not allowing you to jump from "some" to "all" without a proper
reasoning process. You want to claim that your limited experience with a
few bicycles gives you a basis for having a universal knowledge of how all
bikes behave. This is a mistake children make all the time; I'm surprised
to catch you doing it.
> The constraint of always keeping hands on the bars is unacceptable.
I agree.
>> Your position, stated in honest terms, is that "Shimmy only occurs
>> on conventional bicycles when rider induced." Your view is that the
>> rider is *always* the cause. Presumably failing to put ones knees
>> against the top tube is "causing" the bike to shimmy?
>
> That's your interpretation. When a coasting bicycle, with no rider
> input, begins to shimmy is not rider induced in my perception. Rider
That's my position.
> induced is when a rider has his hands on the bars and the bicycle
> begins to shimmy.
This is the point you have not provided any evidence for.
> With the damping of hands and arms on the bars,
> shimmy must be induced by an input from the rider. I have explained
> how that occurs.
You are assuming that a bike cannot possibly have a resonance that is so
powerful that normal hand-dampening can't overcome it. You therefore
conclude that any shimmy while the hands are on the bike must have come
from the hands inducing it.
Again, you have no basis for this "cannot possibly" assumption other than
your own personal observations on a few bikes, combined with perhaps some
anecdotal evidence from a few friends and people you've met on the
internet.
Armed with this faulty assumption, you then brush aside any new evidence to
the contrary, using character attacks. As in when someone says "I didn't
induce that shimmy", you proceed to argue not on any scientific grounds,
nor do you ask for details and try to examine why such a thing would occur,
but instead you start making up stories about what this person must have
been doing (like he was scared or cold or something). You have no evidence
for any of these things; you're reasoning is purely circular, based on your
dogmatically-held premise.
>> The truth of the matter is that shimmy is coming from some
>> *undesirable*, unpredictable harmonic oscillation. Bikes are not
>> designed to shimmy; they shimmy due to factors that are apparently
>> beyond current design practices to overcome without making undue
>> compromises. I.e., the only way they know how to fix the problem is
>> to fiddle with components or hack the design by adding dampeners.
>
> As you may have noticed, it is not a serious problem and I have not
> heard any people with whom I ride complain about it interfering with
> their riding, safety or convenience.
Again we see the faulty reasoning: no one in your little corner of the
universe experiences it, therefore it doesn't exist.
> There are plenty of tall racers
> whose bicycles will shimmy if given the opportunity. They never even
> mention it. I have such a bicycle that will shimmy and can test
> wheels whose makers claim they are shimmy resistant and show that they
> are mistaken. My current bicycle has carried me over more than
> 200,000 miles on all sorts of roads and trails at speeds over 100km/h
> without incident. It is NOT a problem.
More personal experiences being puffed up into specious generalizations.
>> The true cause is the complete system of bike and rider, *but the
>> bicycle designer's job is to account for the full range of
>> reasonable rider variations*. If the designer knows that some
>> riders will be 150lbs, some will be 220lbs, then the frame must
>> withstand that range of weights. If he knows that the rider may sit
>> straight up, or lean almost over the handlebars, then he must
>> account for that. Likewise he must account for various grips on the
>> handlebars.
>
> I take it you want to write specifications for bicycle safety on
> shimmy that you state you do not understand.
No, and I don't see how you came to that conclusion.
> On the other hand, when does your bicycle shimmy
> and what have you done to understand it?
I have noticed two shimmy modes, one similar to the one you describe which
is quite innocuous, and one that is violent. The former mode I don't really
care about, except for its possible connection to the latter. The latter
mode just barely presented itself, and I am in the process of trying to
understand it.
>> Perhaps what you mean to say, is that given the current state of the
>> art, it is the rider's *responsibility*, for the sake of his own
>> safety, to be able to respond correctly to shimmy. I agree with
>> that. But saying it that way instead of the way you put it leaves
>> room for designers to have a healthy frustration over the issue and
>> not be complacent about it. It leaves room for a clever engineer
>> with his sights set on the problem to solve it elegantly.
>
> Do it!
Let's leave your Sunday School lessons out of this; they have little
relevance here.
>> As an expert you should be doing what you can to encourage these
>> kinds of improvements, not providing rationalizations for the
>> evasion of a definite design problem.
>
> It's called "this kind of thing" or "these things", not both.
?
> I'm waiting for someone, with better insights than I, to solve this.
Well this takes care of one half of my issue with what you've written. Now
if we can just get rid of those hasty generalizations.
> From motor vehicles I see that they do not have a solution other than
> steering dampers. With motor power, such devices are bearable. It's
> so old that before I rode a motorcycle I heard of "tank slappers" and
> "sun-fishing".
You might consider that with motor vehicles, there's not much motivation for
the elegant solution. Dampeners work, and they aren't a significant design
compromise, so why bother looking for any better solution? With bikes
dampeners are a huge compromise, so it's a huge mistake to make the
comparison you're making. It only leads to apathy toward the problem.
Shayne Wissler
Sam Huffman
> You are assuming that a bike cannot possibly have a resonance that is so
> powerful that normal hand-dampening can't overcome it. You therefore
> conclude that any shimmy while the hands are on the bike must have come
> from the hands inducing it.
>
> Again, you have no basis for this "cannot possibly" assumption other than
> your own personal observations on a few bikes, combined with perhaps some
> anecdotal evidence from a few friends and people you've met on the
> internet.
I'd add that Jobst mentioned recently that speeds under 30mph were all that is
needed to cause shimmy. I have a mild shimmy at around 18mph, which I could
ride with indefinitely, but the violent wobble I've experienced recently at
35-40mph (both with and without hands on the bars, but only unmanageable
with hands off) is entirely different.
It sounds like others who have experienced this violent shimmy mode also
encountered it well above 30mph. In my case I was neither cold nor scared
(well, not before the shimmy anyway), so I don't believe it was induced by the
rider.
Sam
jobst....@stanfordalumni.org
>> As you may have noticed, it is not a serious problem and I have not
>> heard any people with whom I ride complain about it interfering with
>> their riding, safety or convenience. There are plenty of tall racers
>> whose bicycles will shimmy if given the opportunity. They never even
>> mention it. I have such a bicycle that will shimmy and can test
>> wheels whose makers claim they are shimmy resistant and show that they
>> are mistaken. My current bicycle has carried me over more than
>> 200,000 miles on all sorts of roads and trails at speeds over 100km/h
>> without incident. It is NOT a problem.
> Nothing personal Jobst, but I have to strongly disagree with you here.
> My old 63cm frame shimmied so bad, it threw me and I broke a hip. I
> don't call 8 weeks on crutches and 12 months of pain "not a problem".
> I still have and still ride those wheels, and they /don't/ shimmy with
> any of my new frames.
> Please mark me down as someone that /has/ mentioned it.
That's not so easy, since I haven't ridden with you. I hope you saw
the qualification in the above paragraph. I don't deny that there are
folks who have fallen. It's just that there are people with different
skills.
Jobst Brandt
jobst....@stanfordalumni.org
Mike Jacoubowsky/Chain Reaction Bicycles
> designer's job is to account for the full range of reasonable rider
> variations*. If the designer knows that some riders will be 150lbs, some
> will be 220lbs, then the frame must withstand that range of weights. If he
> knows that the rider may sit straight up, or lean almost over the
> handlebars, then he must account for that. Likewise he must account for
> various grips on the handlebars.
[beware of personal anecdotes and ramblings to follow]
Can you design a frame that handles nicely around town at 15 miles per hour
as well as being stable at 40 miles per hour in a crosswind, *without*
taking rider handling & skills into account? How heavy would the frame need
to be? What other characteristics would accompany something so rigid that
any shimmy would occur in a frequency range not enhanced by the rider?
Manufacturers would love to do away with complaints about bike shimmy, for
reasons that this thread have made obvious. But to rehash what's already
been covered in this thread, it's a very frustrating issue because very few
riders ever experience it, and because it deals with a combination of rider
& bike.
The current thread is particularly interesting, because the shimmy didn't
appear until after the rider changed handlebar position. Thus we know that
the bike was originally stable, and have a darned good idea of how to bring
stability back to it. In other words, it's not a JRA (just riding along)
type of thing.
My main point is that there's been an implication in this thread that
manufacturers don't care or bother with this sort of thing, and that's
simply untrue. A lot of thought and care goes into designing a frame that's
inherently stable under nearly all conditions. It's in the manufacturer's
best interest to do so; the fear of lawsuits provides a powerful incentive
to manufacture something that's easily rideable.
My own experience comes from the real world (our customers), not a great
understanding of physics. And in that real world, we find that those rare
instances of shimmy are typically found with very large (59cm+) steel frames
*and* moderate-sized frames with very light riders. The big-frame guys
often find their shimmy issues solved, or at least greatly reduced, by going
to wider tires. I've found little correlation between changes in stem
length and shimmy although, curiously, height has been an issue (curiously
because that happens also to have been what may have initiated the shimmy in
this thread).
The really light rider on the 56cm frame in a crosswind? That's a tougher
one. Wider tires help, but that person is so light that a 28c tire, or even
25c, often seems inappropriate. I had one customer who we changed the fork
out several times (differing offsets and stiffness) with very little effect.
Once a crosswind hit her, it was all over. Different wheels, a bit better,
but not much. But once we got her on a bike with a very different position,
all was well. She wouldn't alter her position on the old bike, which made
it difficult to know for sure what "cured" the problem.
And on a personal observation, I've only had a shimmy issue once. I
remember it well- it was the Steinbeck Century in 1992, my very first ride
on a brand new 5200. I was descending Los Lorelas Grade (I might have
really botched the spelling!) from Carmel Valley to Highway 89, and at about
40 miles per hour developed quite a nasty wobble. Slowing down made it
better, but I wisely chose to simply stop, check the bike over, relax a bit
and then start back down the hill again. It absolutely, positively never
happened again. Obviously I changed something about my position on the bike
such that it didn't happen again, but I don't know exactly what. However, a
good many years of racing and getting myself into and out of very tight
situations may have helped; it's not as if I didn't know how to handle a
bike... most likely I made an almost automatic adjustment.to how I rode it.
Nothing new to me, just as I adapted between my two racing bikes in the
way-back days (a Cinelli and Bob Jackson with radically-different
geometries). Each one rode nicely, but very differently.
--Mike--
Chain Reaction Bicycles
www.ChainReaction.com
"Shayne Wissler" <thal...@nospam.yahoo.com> wrote in message
news:%j2fb.664762$Ho3.137294@sccrnsc03...
Shayne Wissler
> Jim Beam writes:
>
>>> As you may have noticed, it is not a serious problem and I have not
>>> heard any people with whom I ride complain about it interfering with
>>> their riding, safety or convenience. There are plenty of tall racers
>>> whose bicycles will shimmy if given the opportunity. They never even
>>> mention it. I have such a bicycle that will shimmy and can test
>>> wheels whose makers claim they are shimmy resistant and show that they
>>> are mistaken. My current bicycle has carried me over more than
>>> 200,000 miles on all sorts of roads and trails at speeds over 100km/h
>>> without incident. It is NOT a problem.
>
>> Nothing personal Jobst, but I have to strongly disagree with you here.
>> My old 63cm frame shimmied so bad, it threw me and I broke a hip. I
>> don't call 8 weeks on crutches and 12 months of pain "not a problem".
>
>> I still have and still ride those wheels, and they /don't/ shimmy with
>> any of my new frames.
>
>> Please mark me down as someone that /has/ mentioned it.
>
> That's not so easy, since I haven't ridden with you.
Jobst, if you are going to restrict your universe to your own backyard,
don't give us these sweeping generalizations. Only a person who has
dilligently, honestly looked at *all* of the relevant data has a right to
such forms of expression.
> I hope you saw
> the qualification in the above paragraph. I don't deny that there are
> folks who have fallen. It's just that there are people with different
> skills.
At least your ad hominem is taking on a more subdued flavor. But it's still
ad hominem, and therefore still illogical. You have no reason to suspect
that Jim his a poor rider except that his experience contradicts your
apriori, hastily gotten, sweeping generalizations. You have not one iota of
evidence to accuse him of lack of skill. It's just a simplistic deduction
you're making from your tenaciously-held premise.
Shayne Wissler
jim beam
> understanding of physics. And in that real world, we find that those rare
> instances of shimmy are typically found with very large (59cm+) steel frames
> *and* moderate-sized frames with very light riders. The big-frame guys
> often find their shimmy issues solved, or at least greatly reduced, by going
> to wider tires. I've found little correlation between changes in stem
> length and shimmy although, curiously, height has been an issue (curiously
> because that happens also to have been what may have initiated the shimmy in
> this thread).
as an experiment, i successfully "re-tuned" my "bad" shimmy-prone frame
with a rear wheel spoked 2.0mm straight gauge drive side, 2.0/1.8/2.0mm
non-drive side. it was never a great frame, but the harmonic was gone
after that.
can you test that on your wider audience and see if it works?
jb
Tim McNamara
Shayne Wissler <thal...@nospam.yahoo.com> wrote:
> You are assuming that a bike cannot possibly have a resonance that
> is so powerful that normal hand-dampening can't overcome it. You
> therefore conclude that any shimmy while the hands are on the bike
> must have come from the hands inducing it.
Your experience was unusual- a previously reliable bike suddenly
provided a violent shimmy and nearly catapulted you from the bike and
endangered your life, or some such. These are not commonly reported
occurrences in this newsgroup, and since they're so dramatic it is
reasonable to expect we'd see a lot of such reports if the event was
common. I can recall one previous thread describing a similar event
in the past couple of years (but I'm getting old, so take that with a
grain of salt).
Now, the shimmy may indeed originate in the hands of the rider- I've
had it happen while shivering from cold just recently, during PBP.
I've seen it happen to other riders. I've had shimmy occur while
riding several of my bicycles- typically on bikes with a handlebar bag
or a really long stem. In one case have I had a sudden surprising
shimmy on a bike not normally prone to that; this shimmy occurred when
I shifted my weight far back on the saddle while descending and
actually felt like it was the back end of the bike that was shimmying
rather than the steering end. When I repositioned myself to a normal
position, the shimmy stopped. "Rider induced" doesn't mean that the
shimmy originates in the hands necessarily, but that something in the
rider's behavior prompted or prolonged the shimmy.
I've seen one case of violent shimmy, but this was actually
consistent. A friend of mine had a De Rosa aluminum bike and matching
fork, which developed a nasty shimmy that made descents quite
dangerous. The shimmy was dramatic enough that riders moved away from
my friend when they saw him going downhill shaking like a leaf. He
didn't have this problem with other bikes, so the problem didn't seem
likely to originate with him. Turned out he had a typical ultra tight
clearance fork, about 1 mm with a 700 x 23, and the tire he was using
was ever so slightly out of round and brushed the underside of the
crown. Replacing the tire cured the problem.
> >> The true cause is the complete system of bike and rider, *but
> >> the bicycle designer's job is to account for the full range of
> >> reasonable rider variations*. If the designer knows that some
> >> riders will be 150lbs, some will be 220lbs, then the frame must
> >> withstand that range of weights. If he knows that the rider may
> >> sit straight up, or lean almost over the handlebars, then he
> >> must account for that. Likewise he must account for various
> >> grips on the handlebars.
> >
> > I take it you want to write specifications for bicycle safety on
> > shimmy that you state you do not understand.
>
> No, and I don't see how you came to that conclusion.
Perhaps from reading your rather arrogant paragraph immediately above
the comment?
> > On the other hand, when does your bicycle shimmy and what have
> > you done to understand it?
>
> I have noticed two shimmy modes, one similar to the one you
> describe which is quite innocuous, and one that is violent. The
> former mode I don't really care about, except for its possible
> connection to the latter. The latter mode just barely presented
> itself, and I am in the process of trying to understand it.
You seem to be in the process of arguing with all and sundry about it,
rather than trying to understand it.
> >> Perhaps what you mean to say, is that given the current state of
> >> the art, it is the rider's *responsibility*, for the sake of his
> >> own safety, to be able to respond correctly to shimmy. I agree
> >> with that. But saying it that way instead of the way you put it
> >> leaves room for designers to have a healthy frustration over the
> >> issue and not be complacent about it. It leaves room for a
> >> clever engineer with his sights set on the problem to solve it
> >> elegantly.
> >
> > Do it!
>
> Let's leave your Sunday School lessons out of this; they have
> little relevance here.
Huh?
> > I'm waiting for someone, with better insights than I, to solve
> > this.
>
> Well this takes care of one half of my issue with what you've
> written. Now if we can just get rid of those hasty generalizations.
Hmmm. "Hasty generalizations?" You're kind of new here, aren't you?
Jobst can be tetchy and does not suffer fools gladly, but he's been
riding bike longer than I've been alive (and I'm 44) and has been an
engineer almost as long as I've been alive. I doubt there's much
that's "hasty" about his conclusions, although perhaps you have not
seen the chains of events, observations and reasoning that has led to
those conclusions.
A Google search in the archives for "frame shimmy" will reveal much
previous discussion- including exactly the kind of vioent shimmy
you're deacribing. ISTR that that discussion was within the past two
years, it provoked a long thread and much interesting experimentation
and discussion. I'm sure you've also been pointed towards the FAQ
article on frame shimmy already.
> > From motor vehicles I see that they do not have a solution other
> > than steering dampers. With motor power, such devices are
> > bearable. It's so old that before I rode a motorcycle I heard of
> > "tank slappers" and "sun-fishing".
>
> You might consider that with motor vehicles, there's not much
> motivation for the elegant solution. Dampeners work, and they
> aren't a significant design compromise, so why bother looking for
> any better solution? With bikes dampeners are a huge compromise, so
> it's a huge mistake to make the comparison you're making. It only
> leads to apathy toward the problem.
Actually, "dampeners" make things wet. "Dampers" control undesireable
movements such as oscillations. A shock absorber is a damper, for
example. As far as "apathy to the problem" goes, your description is
highly unusual and therefore somewhat suspect as to being something
that can be "designed for."
jobst....@stanfordalumni.org
>>>> Shimmy only occurs on conventional bicycles either when rider
>>>> induced or while riding no-hands.
>>> I keep seeing you repeat this but I have never seen you
>>> substantiate it. And it flies in the face of my experience.
>> You are ignoring the examples I cite and the tests that I have done,
> No, I'm just not allowing you to jump from "some" to "all" without a
> proper reasoning process. You want to claim that your limited
> experience with a few bicycles gives you a basis for having a
> universal knowledge of how all bikes behave. This is a mistake
> children make all the time; I'm surprised to catch you doing it.
You sound like the reviews I got about "the Bicycle Wheel" when it was
first published... "how many wheels have you built anyway" in contrast
to the thousand or more these critics had built i had certainly no
more than 50 to my credits. The difference is that I observed what
was occurring and analyzed why. Observations, some logic and an
understanding of materials put these things in order the same as my
investigation of shimmy. You don't have to have a PhD in shimmy to
analyze what is occurring. This phenomenon has only one mode, that of
caster instability. In the bicycle, gyroscopic forces (that do not
affect shopping cart wheels for instance) also come into play.
>> The constraint of always keeping hands on the bars is unacceptable.
> I agree.
>>> Your position, stated in honest terms, is that "Shimmy only occurs
>>> on conventional bicycles when rider induced." Your view is that
>>> the rider is *always* the cause. Presumably failing to put ones
>>> knees against the top tube is "causing" the bike to shimmy?
>> That's your interpretation. When a coasting bicycle, with no rider
>> input, begins to shimmy is not rider induced in my perception.
> That's my position.
>> Rider induced occurs when a rider has his hands on the bars and the
>> bicycle begins to shimmy.
> This is the point you have not provided any evidence for.
I believe I have. I cited the instance where a rider could not start
on a cold morning, a rider who was never bothered by shimmy previously
(or since) but had shimmy from a standstill, and my own experience
when shivering gold on a descent. These were exceptional cases that
demonstrated that riders who otherwise have no shimmy problems, can
experience them and in both of these examples they were clearly rider
induced. Logically one must ask, why now? What are these other riders
experiencing when "out of the blue" the bicycle becomes unstable?
>> With the damping of hands and arms on the bars, shimmy must be
>> induced by an input from the rider. I have explained how that
>> occurs.
It cannot.
> You are assuming that a bike cannot possibly have a resonance that
> is so powerful that normal hand-dampening can't overcome it. You
> therefore conclude that any shimmy while the hands are on the bike
> must have come from the hands inducing it.
I didn't say that. A no-hands ridden bicycle can develop this but
with the riders hands on the bars, it can only do that with feedback
from the muscles of the rider. We are talking about bicycles of
which thousands were sold, not some unique geometry and material. If
things were as you see them, there would be a massive complaint from
many people.
> Again, you have no basis for this "cannot possibly" assumption other than
> your own personal observations on a few bikes, combined with perhaps some
> anecdotal evidence from a few friends and people you've met on the
> internet.
Whether they are my "observations" or my "own personal" ones implies
that all people are as stupid as the worst and you cannot believe
anything they say. How about proposing another source for shimmy on a
bicycle the rider has ridden without problems for more than a thousand
representative miles before experiencing shimmy to the point of
crashing on a familiar route.
> Armed with this faulty assumption, you then brush aside any new
> evidence to the contrary, using character attacks.
What you call character attacks are replies in kind to people of your
persuasion whose snide comments you find appropriate. If I call their
comments for what they are, you take it as an ad hominem.
> As in when someone says "I didn't induce that shimmy", you proceed
> to argue not on any scientific grounds, nor do you ask for details
> and try to examine why such a thing would occur, but instead you
> start making up stories about what this person must have been doing
> (like he was scared or cold or something). You have no evidence for
> any of these things; you're reasoning is purely circular, based on
> your dogmatically-held premise.
I think it appropriate to suggest alternate scenarios for the
occurrence of shimmy that I have observed. A tense "death grip" is
ideal for human reinforcement of the bicycle's natural resonance. The
term "death grip" was unwittingly offered by victims of the problem.
>>> The truth of the matter is that shimmy is coming from some
>>> *undesirable*, unpredictable harmonic oscillation. Bikes are not
>>> designed to shimmy; they shimmy due to factors that are apparently
>>> beyond current design practices to overcome without making undue
>>> compromises. I.e., the only way they know how to fix the problem
>>> is to fiddle with components or hack the design by adding
>>> dampeners.
>> As you may have noticed, it is not a serious problem and I have not
>> heard any people with whom I ride complain about it interfering with
>> their riding, safety or convenience.
> Again we see the faulty reasoning: no one in your little corner of the
> universe experiences it, therefore it doesn't exist.
I think you missed the point. I don't go bicycling with people who
aren't well versed in bicycle handling or the converse, these people
who have these problems don't come on bike rides that I prefer to
take, to put it more bluntly. I think you are wilfully
misinterpreting what I say. If you look in the FAQ item, you'll see
that it does exist and that this piece was written long ago before
there was much talk of it.
>> There are plenty of tall racers whose bicycles will shimmy if given
>> the opportunity. They never even mention it. I have such a
>> bicycle that will shimmy and can test wheels whose makers claim
>> they are shimmy resistant and show that they are mistaken. My
>> current bicycle has carried me over more than 200,000 miles on all
>> sorts of roads and trails at speeds over 100km/h without incident.
>> It is NOT a problem.
> More personal experiences being puffed up into specious
> generalizations.
Please expand on that. What is a specious generalization in that
statement?
>>> The true cause is the complete system of bike and rider, *but the
>>> bicycle designer's job is to account for the full range of
>>> reasonable rider variations*. If the designer knows that some
>>> riders will be 150lbs, some will be 220lbs, then the frame must
>>> withstand that range of weights. If he knows that the rider may
>>> sit straight up, or lean almost over the handlebars, then he must
>>> account for that. Likewise he must account for various grips on
>>> the handlebars.
>> I take it you want to write specifications for bicycle safety on
>> shimmy that you state you do not understand.
> No, and I don't see how you came to that conclusion.
What you stated sounded like an indictment against frames that can
shimmy and that it is unreasonable. That sounds like the beginning of
a specification of what is acceptable and not, to me.
>> On the other hand, when does your bicycle shimmy and what have you
>> done to understand it?
> I have noticed two shimmy modes, one similar to the one you describe
> which is quite innocuous, and one that is violent. The former mode
> I don't really care about, except for its possible connection to the
> latter. The latter mode just barely presented itself, and I am in
> the process of trying to understand it.
What is the difference between these to as you see them other than
amplitude?
>>> Perhaps what you mean to say, is that given the current state of
>>> the art, it is the rider's *responsibility*, for the sake of his
>>> own safety, to be able to respond correctly to shimmy. I agree
>>> with that. But saying it that way instead of the way you put it
>>> leaves room for designers to have a healthy frustration over the
>>> issue and not be complacent about it. It leaves room for a clever
>>> engineer with his sights set on the problem to solve it elegantly.
>> Do it!
> Let's leave your Sunday School lessons out of this; they have little
> relevance here.
I don't understand what you mean there. You make a proposal and I
encourage you to put it into action.
>>> As an expert you should be doing what you can to encourage these
>>> kinds of improvements, not providing rationalizations for the
>>> evasion of a definite design problem.
>> It's called "this kind of thing" or "these things", not both.
> ?
>> I'm waiting for someone, with better insights than I, to solve this.
> Well this takes care of one half of my issue with what you've
> written. Now if we can just get rid of those hasty generalizations.
Which ones in particular and why do you call them that?
>> From motor vehicles I see that they do not have a solution other
>> than steering dampers. With motor power, such devices are
>> bearable. It's so old that before I rode a motorcycle I heard of
>> "tank slappers" and "sun-fishing".
> You might consider that with motor vehicles, there's not much
> motivation for the elegant solution. Dampeners work, and they
> aren't a significant design compromise, so why bother looking for
> any better solution? With bikes dampeners are a huge compromise, so
> it's a huge mistake to make the comparison you're making. It only
> leads to apathy toward the problem.
I have no doubt that other solutions would be welcome, but no one has
offered one. Having worked in automotive design, I am sure they spend
far more time looking for economical and reliable solutions to such
problems than bicycle companies do.
Jobst Brandt
jobst....@stanfordalumni.org
Rick Onanian
<thalesN...@yahoo.com> wrote:
>I don't think either side of this argument will dispute the fact that a
>shimmy can cause you to crash. You figure out the rest.
Actually, there are a lot of people here who think it's near
impossible to crash a bicycle, and that in the event of a crash,
it's near impossible to be badly injured...
>Shayne Wissler
--
Rick "Smartass" Onanian
jobst....@stanfordalumni.org
> I'd add that Jobst mentioned recently that speeds under 30mph were
> all that is needed to cause shimmy. I have a mild shimmy at around
> 18mph, which I could ride with indefinitely, but the violent wobble
> I've experienced recently at 35-40mph (both with and without hands
> on the bars, but only unmanageable with hands off) is entirely
> different.
I see no conflict there. Just because shimmy can initiate below 30mph
or as you say as low as 18mph does not mean that it cannot increase in
amplitude with higher speed. I don't see why you think I said what
you seem to imply, that shimmy cannot occur above 30mph.
> It sounds like others who have experienced this violent shimmy mode
> also encountered it well above 30mph. In my case I was neither cold
> nor scared (well, not before the shimmy anyway), so I don't believe
> it was induced by the rider.
If you get a shimmy with hands on the bars, you are most likely not
going to stop it by grasping the bars firmly and tensing the arm
muscles, both natural reactions to bicycle instability. I think
therein lies a large part of the problem.
Jobst Brandt
jobst....@stanfordalumni.org
Shayne Wissler
> In article <TK3fb.24400$%h1.13595@sccrnsc02>,
> Shayne Wissler <thal...@nospam.yahoo.com> wrote:
>
>> You are assuming that a bike cannot possibly have a resonance that
>> is so powerful that normal hand-dampening can't overcome it. You
>> therefore conclude that any shimmy while the hands are on the bike
>> must have come from the hands inducing it.
>
> Your experience was unusual- a previously reliable bike suddenly
> provided a violent shimmy and nearly catapulted you from the bike and
> endangered your life, or some such. These are not commonly reported
> occurrences in this newsgroup, and since they're so dramatic it is
> reasonable to expect we'd see a lot of such reports if the event was
> common. I can recall one previous thread describing a similar event
> in the past couple of years (but I'm getting old, so take that with a
> grain of salt).
It's definitely unusual to me. I've ridden bikes for several years and
descended this particular canyon I don't know how many times, and in all
that time I've never experienced anything like this.
> likely to originate with him. Turned out he had a typical ultra tight
> clearance fork, about 1 mm with a 700 x 23, and the tire he was using
> was ever so slightly out of round and brushed the underside of the
> crown. Replacing the tire cured the problem.
Hmmm. Neither my front nor my back tires are perfectly round. The front rim
seems mostly round and true, but the tire itself is off by 1-2mm at certain
points (Bontrager 700x23 Race X Lite Silica). This is the recently
installed tire.
>> >> The true cause is the complete system of bike and rider, *but
>> >> the bicycle designer's job is to account for the full range of
>> >> reasonable rider variations*. If the designer knows that some
>> >> riders will be 150lbs, some will be 220lbs, then the frame must
>> >> withstand that range of weights. If he knows that the rider may
>> >> sit straight up, or lean almost over the handlebars, then he
>> >> must account for that. Likewise he must account for various
>> >> grips on the handlebars.
>> >
>> > I take it you want to write specifications for bicycle safety on
>> > shimmy that you state you do not understand.
>>
>> No, and I don't see how you came to that conclusion.
>
> Perhaps from reading your rather arrogant paragraph immediately above
> the comment?
I don't see anything in the arrogant paragraph claiming that I want to write
specifications.
>> > On the other hand, when does your bicycle shimmy and what have
>> > you done to understand it?
>>
>> I have noticed two shimmy modes, one similar to the one you
>> describe which is quite innocuous, and one that is violent. The
>> former mode I don't really care about, except for its possible
>> connection to the latter. The latter mode just barely presented
>> itself, and I am in the process of trying to understand it.
>
> You seem to be in the process of arguing with all and sundry about it,
> rather than trying to understand it.
It's not either/or. I can disagree with Jobst's methods and try to
understand at the same time.
>> >> Perhaps what you mean to say, is that given the current state of
>> >> the art, it is the rider's *responsibility*, for the sake of his
>> >> own safety, to be able to respond correctly to shimmy. I agree
>> >> with that. But saying it that way instead of the way you put it
>> >> leaves room for designers to have a healthy frustration over the
>> >> issue and not be complacent about it. It leaves room for a
>> >> clever engineer with his sights set on the problem to solve it
>> >> elegantly.
>> >
>> > Do it!
>>
>> Let's leave your Sunday School lessons out of this; they have
>> little relevance here.
>
> Huh?
Just examine the premises behind his statement. If you don't know how to do
that then you probably wouldn't appreciate me doing it for you.
>> > I'm waiting for someone, with better insights than I, to solve
>> > this.
>>
>> Well this takes care of one half of my issue with what you've
>> written. Now if we can just get rid of those hasty generalizations.
>
> Hmmm. "Hasty generalizations?" You're kind of new here, aren't you?
Ad hominem is apparently a favorite technique here. Exactly how does being
new to the forum impact my ability to discern Jobst's propensity for
jumping to conclusions?
> Jobst can be tetchy and does not suffer fools gladly, but he's been
> riding bike longer than I've been alive (and I'm 44) and has been an
Unfortunately, age does not always lead one to wisdom. In fact it rarely
does. So please spare me the age crap.
> engineer almost as long as I've been alive. I doubt there's much
> that's "hasty" about his conclusions, although perhaps you have not
> seen the chains of events, observations and reasoning that has led to
> those conclusions.
I see all of the chains that he presents. I've read his FAQ, as well as
perused his other musings on this topic. So far I'd say that he's providing
some good practical advice, but that his theoretical understanding leaves
much to be desired.
> A Google search in the archives for "frame shimmy" will reveal much
> previous discussion- including exactly the kind of vioent shimmy
> you're deacribing. ISTR that that discussion was within the past two
> years, it provoked a long thread and much interesting experimentation
> and discussion.
I've looked through some of the old writings, but perhaps I missed some good
posts.
>> > From motor vehicles I see that they do not have a solution other
>> > than steering dampers. With motor power, such devices are
>> > bearable. It's so old that before I rode a motorcycle I heard of
>> > "tank slappers" and "sun-fishing".
>>
>> You might consider that with motor vehicles, there's not much
>> motivation for the elegant solution. Dampeners work, and they
>> aren't a significant design compromise, so why bother looking for
>> any better solution? With bikes dampeners are a huge compromise, so
>> it's a huge mistake to make the comparison you're making. It only
>> leads to apathy toward the problem.
>
> Actually, "dampeners" make things wet. "Dampers" control undesireable
> movements such as oscillations. A shock absorber is a damper, for
> example.
How old did you say you were again? You certainly don't act any older than a
college student.
> As far as "apathy to the problem" goes, your description is
> highly unusual and therefore somewhat suspect as to being something
> that can be "designed for."
Perhaps there is something wrong with my bike. Perhaps the 1-2mm out of
round is too much?
Shayne Wissler
jim beam
> analyze what is occurring. This phenomenon has only one mode, that of
> caster instability.
whoa. stop right there. that's a gross mis-statement.
please, you need to correct that.
> In the bicycle, gyroscopic forces (that do not
> affect shopping cart wheels for instance) also come into play.
gyro forces are different from imbalance problems. red herring.
--<snip>--
> What you stated sounded like an indictment against frames that can
> shimmy and that it is unreasonable. That sounds like the beginning of
> a specification of what is acceptable and not, to me.
from my experience, a frame that is prone to shimmy is dangerous and
completely unacceptable. indictment of such frames is absolutely
appropriate.
--<snip>--
>>I have noticed two shimmy modes, one similar to the one you describe
>>which is quite innocuous, and one that is violent. The former mode
>>I don't really care about, except for its possible connection to the
>>latter. The latter mode just barely presented itself, and I am in
>>the process of trying to understand it.
>
> What is the difference between these to as you see them other than
> amplitude?
frequency. harmonics are a primary fundamental part of this equation.
how can a suspension engineer not know this?
jb
jobst....@stanfordalumni.org
>> I don't think either side of this argument will dispute the fact
>> that a shimmy can cause you to crash. You figure out the rest.
I don't believe that because you don't need to watch the shimmy build
up and get to the point where it can damage the front wheel (or roll a
tire), the only reason to crash. A shimmy can be arrested by the
means described in the FAQ. On the other hand, a rider who has never
experienced shimmy could be caught off guard and fail to invoke the
appropriate response.
A shimmy control class for new riders might be in order, just as
driver training teaches controlling spin-outs on a wet skid pad. The
problem with that is the riders would first need to learn how to ride
no-hands so they can observe shimmy. That might be the hardest part.
I think that considering the forces that a few centimeters trail can
exert on steering, it should be apparent that any rider is strong
enough to resist the motion. The frequency that coincides with
muscular response time is the problem and riders cannot recognize that
because they are so intimately involved in the motion. Shimmy can
only occur on the bicycles in question either while riding no-hands or
with rider reinforcement.
Jobst Brandt
jobst....@stanfordalumni.org
Mike Latondresse
news:qappnv89j5usod5j3...@4ax.com:
So smartass what the hell is that supposed to mean, that you can crash,
sure, do crits and you do lots, few of which are your fault. You can
get hurt, you can get hurt on your front steps. Do many or any riders
crash from a shimmy, I don't think many, if any, do and if you do
perhaps you sould give up cycling.
Shayne Wissler
>>> On the other hand, when does your bicycle shimmy and what have you
>>> done to understand it?
>
>> I have noticed two shimmy modes, one similar to the one you describe
>> which is quite innocuous, and one that is violent. The former mode
>> I don't really care about, except for its possible connection to the
>> latter. The latter mode just barely presented itself, and I am in
>> the process of trying to understand it.
>
> What is the difference between these to as you see them other than
> amplitude?
- The harsh shimmy happened at 42MPH, the mild one is usually at around
20MPH
- The harsh one happened while holding the handlebars, the mild one happens
while riding no-hands
- The harsh one felt like the bike was hooked to some vibrating machine. It
was not possible for me to dampen the vibration significantly with my
hands. I had to slow down. The mild one ceases soon after I grab the
handlebars.
- The harsh one seemed to spontaneously occur; the change from stability to
instability was very rapid; the amplitude change was from 0 to some number
of inches in a split second, and the amplitude did not seem to vary except
when I braked. Further, the frequency seemed quite fixed as well, and not
appreciably subject to hand action (but did slow down when I braked). The
mild one seems to have more variance in the amplitude and in the frequency,
and seems to be far more subject to my actions.
- The harsh one felt radical enough to bend the rim. The mild one has far
less energy.
I can't recall any other differences at the moment.
Shayne Wissler
Shayne Wissler
> Shayne Wissler writes:
>
>>> I don't think either side of this argument will dispute the fact
>>> that a shimmy can cause you to crash. You figure out the rest.
>
> I don't believe that because you don't need to watch the shimmy build
> up and get to the point where it can damage the front wheel (or roll a
> tire), the only reason to crash.
Your shimmy model needs revision. Don't feel bad. Ptolemy was a smart fellow
but his planetary model broke down too.
The shimmy I experienced was extreme and immediate--there was no perceptible
buildup in intensity.
> A shimmy can be arrested by the
> means described in the FAQ. On the other hand, a rider who has never
> experienced shimmy could be caught off guard and fail to invoke the
> appropriate response.
Correction: the shimmy that you recognize can be arrested by the means
described in your FAQ.
Shayne Wissler
jobst....@stanfordalumni.org
>> You don't have to have a PhD in shimmy to analyze what is
>> occurring. This phenomenon has only one mode, that of caster
>> instability.
> Whoa. Stop right there. That's a gross mis-statement.
> Please, you need to correct that.
How about offering what you find inaccurate about that. Caster
instability is the steering overshoot of a wheel with trail
oscillating about its steering axis.
>> In the bicycle, gyroscopic forces (that do not affect shopping cart
>> wheels for instance) also come into play.
> gyro forces are different from imbalance problems. red herring.
There are no imbalance problems in the bicycle shimmy. That was
proposed in the last swell of indignation on this subject a while ago.
I reported the results of balance and imbalance as well as change in
weight of the wheel. There was no change in the shimmy except for a
lower frequency for the heavy wheel.
> --<snip>--
>> What you stated sounded like an indictment against frames that can
>> shimmy and that it is unreasonable. That sounds like the beginning
>> of a specification of what is acceptable and not, to me.
> From my experience, a frame that is prone to shimmy is dangerous and
> completely unacceptable. Indictment of such frames is absolutely
> appropriate.
As I pointed out, most larger frames will shimmy if allowed to do so.
I think you'll have to relegate a large number of frames to the
unreasonable.
> --<snip>--
>>> I have noticed two shimmy modes, one similar to the one you
>>> describe which is quite innocuous, and one that is violent. The
>>> former mode I don't really care about, except for its possible
>>> connection to the latter. The latter mode just barely presented
>>> itself, and I am in the process of trying to understand it.
>> What is the difference between these to as you see them other than
>> amplitude?
> Frequency. Harmonics are a primary fundamental part of this
> equation. How can a suspension engineer not know this?
On the same bicycle with the same equipment, I would like you to
demonstrate different frequencies of shimmy. Having tested shimmy
from small to large amplitude, I have fond no change in frequency. In
fact, there are accelerometer tests that show constant frequency over
a wide range of amplitude. These were made by a major bicycle company
and are not in my possession. So let me put it this way, you are
making this up of thin air.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
>>> I don't think either side of this argument will dispute the fact
>>> that a shimmy can cause you to crash. You figure out the rest.
>> I don't believe that because you don't need to watch the shimmy
>> build up and get to the point where it can damage the front wheel
>> (or roll a tire), the only reason to crash.
> Your shimmy model needs revision. Don't feel bad. Ptolemy was a
> smart fellow but his planetary model broke down too.
Snide comment aside, what do you mean the model needs revision? Here
we have an oscillation that start from zero amplitude and reaches an
excursion in time that, depending on speed can become damaging.
> The shimmy I experienced was extreme and immediate--there was no
> perceptible buildup in intensity.
This is not possible. The bicycle was traveling straight ahead in a
continuous line and began oscillating. Your perception that it was at
maximum, instantly is not possible because that requires "infinite" or
at least a large force. From where does this large lateral force or
steering torque arise? This is hocus pocus. You must realize that
being the subject of this loss of control, you are not perceiving it
accurately.
>> A shimmy can be arrested by the means described in the FAQ. On the
>> other hand, a rider who has never experienced shimmy could be
>> caught off guard and fail to invoke the appropriate response.
> Correction: the shimmy that you recognize can be arrested by the
> means described in your FAQ.
There is only one shimmy and it can have varying amplitude. It is
the riders business to arrest it before it gets out of hand, so to
speak.
Jobst Brandt
jobst....@stanfordalumni.org
Shayne Wissler
> Shayne Wissler writes:
>
>>>> I don't think either side of this argument will dispute the fact
>>>> that a shimmy can cause you to crash. You figure out the rest.
>
>>> I don't believe that because you don't need to watch the shimmy
>>> build up and get to the point where it can damage the front wheel
>>> (or roll a tire), the only reason to crash.
>
>> Your shimmy model needs revision. Don't feel bad. Ptolemy was a
>> smart fellow but his planetary model broke down too.
>
> Snide comment aside, what do you mean the model needs revision? Here
> we have an oscillation that start from zero amplitude and reaches an
> excursion in time that, depending on speed can become damaging.
Speak in terms of cause and not merely effect and you'll see your error.
Which interestingly was precisely same error that messed up Ptolemy's
model.
>> The shimmy I experienced was extreme and immediate--there was no
>> perceptible buildup in intensity.
>
> This is not possible. The bicycle was traveling straight ahead in a
> continuous line and began oscillating. Your perception that it was at
> maximum, instantly is not possible because that requires "infinite" or
> at least a large force.
Well obviously it's not possible to instantaneously go from zero to moving.
But I never said it did that. Don't conflate percepts with reality.
I said that it went so fast that it was not possible for me to perceive the
change (without fancy cameras anyway). One split second it was stable, the
next it was wobbling like crazy. With this kind of effect, there's no way
to follow your prescription of stopping it before it gets going.
> From where does this large lateral force or
> steering torque arise?
A valid question. I presume it had something to do with my high forward
momentum, from which there was ample energy to draw.
> This is hocus pocus.
I think you just lack imagination. A side effect of indulging in dogma.
> You must realize that
> being the subject of this loss of control, you are not perceiving it
> accurately.
Not the "rider is deluded" argument again... Apparently you're versed in
modern pseudo-psychology as well as engineering? Let me guess, are you a
fan of B.F. Skinner?
If you want to blank out facts with that be my guest. I can't force you out
of fantasy land.
>>> A shimmy can be arrested by the means described in the FAQ. On the
>>> other hand, a rider who has never experienced shimmy could be
>>> caught off guard and fail to invoke the appropriate response.
>
>> Correction: the shimmy that you recognize can be arrested by the
>> means described in your FAQ.
>
> There is only one shimmy and it can have varying amplitude. It is
> the riders business to arrest it before it gets out of hand, so to
> speak.
Another dogma rears its head: You presume that the change in amplitude
simply cannot happen so fast (at 42MPH going downhill) that it is beyond
the rider's neurological capacity to arrest it before it reaches its peak.
That's what happens when you indulge one dogma, it leads to another, and
another, and another. You have to keep tacking them on in order to keep the
original one from falling over in the face of the facts. See Ptolemy's
obfuscated model for more hints.
Shayne Wissler
jim beam
> instability is the steering overshoot of a wheel with trail
> oscillating about its steering axis.
i know what it is. you do the math - you know the range of angles &
trails. it's not the cause of the problem! and that statement still
doesn't explain how two frames, built to identical geometry but
different tube specs [for example] can have different shimmy
characteristics! i know because i've had two identical frames built to
the same geometry but with different tube. the "standard" size tube
frame was unstable. the oversize tube frame /is/ stable. using the
same tires, wheels, etc.
this is a resonance issue with the frame and wheel combination being the
most substantial participants.
> There are no imbalance problems in the bicycle shimmy.
fundamentally incorrect. if a system has an harmonic and an oscillating
imbalance coincides with that harmonic, you have a tacoma narrows bridge
situation.
> As I pointed out, most larger frames will shimmy if allowed to do so.
> I think you'll have to relegate a large number of frames to the
> unreasonable.
if need be, yes! large light older frames are /chronic/ for this.
older "heavy" frames are not so bad. modern frames that take advantage
of large diameter tubes are great, /if/ the manufacturer does not
substantially negate by ovalizing. fortunately most volume
manufacturers seem switched on to the problem these days. not our
favorite topic, but upgrades are a good thing.
> you are
> making this up of thin air.
why would i? what's my advantage? i can't wash my laundry in public
and hope people won't notice my personal "boxers or briefs" preferences.
how can i possibly b.s. you in a public forum and not get called on
it? a contrary argument is /not/ an attack.
jim beam
> 20MPH
jobst, this looks like a harmonic to me.
jb.
Shayne Wissler
>> Caster
>> instability is the steering overshoot of a wheel with trail
>> oscillating about its steering axis.
>
> i know what it is. you do the math - you know the range of angles &
> trails. it's not the cause of the problem!
It is an effect. Modeling effects while ignoring causes is a favorite
pastime of some modern scientists--and some old ones (Ptolemy). It is a
fundamentally wrong-headed approach, even bizarrely so, but rarely is it
possible to jar someone out of his effect-oriented fixation.
Shayne Wissler
Mike Jacoubowsky
> with a rear wheel spoked 2.0mm straight gauge drive side, 2.0/1.8/2.0mm
> non-drive side. it was never a great frame, but the harmonic was gone
> after that.
>
> can you test that on your wider audience and see if it works?
We've tried different wheels, with less success than simply switching to a
wider tire.
--Mike-- Chain Reaction Bicycles
http://www.ChainReactionBicycles.com
"jim beam" <u...@ftc.gov> wrote in message
news:x55fb.11222$Hh3...@newssvr25.news.prodigy.com...
David Damerell
>Actually, there are a lot of people here who think it's near
>impossible to crash a bicycle, and that in the event of a crash,
>it's near impossible to be badly injured...
Are you morally opposed to telling the truth, or do you just lie about
people for the hell of it?
--
David Damerell <dame...@chiark.greenend.org.uk> Distortion Field!
Tom Nakashima
It is not due to the size of the bicycle, nor is it frame material. It is
also
not due to frame alignment or loose headsets, tire pressure or even
death-grip,
however these may be small factors to the problem.
The dead give-away is dampener.
MOST every bicycle rider has two dampeners.
Any guess what they are?
Answer: your arms!
Sometimes we take for granted that they're there, and play a major role
in shock absorbing the bike and steering. One example is watch a first time
child ride a two wheel bike. Notice how they how they're trying
like mad to control the bike by steering.
I made a mistake in my last statement when I said shimmy occurs on a
straightaway.
It doesn't, nor does it occur when climbing with a bicycle. It does however
occur
on a descent because of the weight distribution to the front.
Here is the test that I performed yesterday.
On a straight descent, doesn't have to be steep, 3-7% is good enough for
about 1/4 to
1/2 mile long with your speed about 20 mph, tighten up both arms on top of
the handlebars.
Your grip doesn't matter that much, in one case I even used my palms on top
of the bar with my fingers up,
But your have to keep the arms tight and straight. I then rocked the
handlebars ever so slightly back
and forth still with my arms tight. The bike started to shimmy. My first
reaction was to try to correct this,
by using force, arms straight and tight to compensate for the wobble, but
the more I tried to correct,
the shimmy got worst. I then loosened up my arms and the bike shimmy started
to correct itself.
So this may explain the shivering and involuntary muscle action to get the
bike to shimmy on a descent?
You can perform this experiment yourself in case you're in doubt.
Mystery solved? Jump in, I would love to hear what you think about this.
-tom
<jobst....@stanfordalumni.org> wrote in message
news:RL1fb.26916$dk4.8...@typhoon.sonic.net...
>
> I didn't see that you tried the test I suggested. Shimmy only occurs
> on conventional bicycles either when rider induced or while riding
> no-hands. You must ride no-hands to perform the "does this bicycle
> shimmy" test. Until you do this you will not get closer to the source
> of your shimmy experience. The course I suggested is my standard one
> for such tests because the grade is uniform, the road smooth and it
> has no traffic problems with its wide and integral bicycle lanes.
>
> Jobst Brandt
> jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
> I believe I may have solved the mystery of the bicycle shimmy. It
> is not due to the size of the bicycle, nor is it frame material. It
> is also not due to frame alignment or loose headsets, tire pressure
> or even death-grip, however these may be small factors to the
> problem.
> I made a mistake in my last statement when I said shimmy occurs on a
> straightaway. It doesn't, nor does it occur when climbing with a
> bicycle. It does however occur on a descent because of the weight
> distribution to the front.
That my be so in your case but coasting down the half mile straight
and smooth section of Sand Hill Road near your place of work is an
ideal shimmy test course. It is straight and bicycles shimmy there.
> Here is the test that I performed yesterday. On a straight descent,
> doesn't have to be steep, 3-7% is good enough for about 1/4 to 1/2
> mile long with your speed about 20 mph, tighten up both arms on top
> of the handlebars. Your grip doesn't matter that much, in one case
> I even used my palms on top of the bar with my fingers up, But your
> have to keep the arms tight and straight. I then rocked the
> handlebars ever so slightly back and forth still with my arms tight.
> The bike started to shimmy. My first reaction was to try to correct
> this, by using force, arms straight and tight to compensate for the
> wobble, but the more I tried to correct, the shimmy got worst. I
> then loosened up my arms and the bike shimmy started to correct
> itself.
I see you still did not perform the shimmy test that I suggested:
>> I didn't see that you tried the test I suggested. Shimmy only
>> occurs on conventional bicycles either when rider induced or while
>> riding no-hands. You must ride no-hands to perform the "does this
>> bicycle shimmy" test. Until you do this you will not get closer to
>> the source of your shimmy experience. The course I suggested is my
>> standard one for such tests because the grade is uniform, the road
>> smooth and it has no traffic problems with its wide and integral
>> bicycle lanes.
> So this may explain the shivering and involuntary muscle action to
> get the bike to shimmy on a descent? You can perform this
> experiment yourself in case you're in doubt. Mystery solved? Jump
> in, I would love to hear what you think about this.
I don't consider it any mystery as I have explained.
Jobst Brandt
jobst....@stanfordalumni.org
Tom Nakashima
I didn't peform this test yet, riding with no hands, knees not touching the
top tube,
riding eastbound from the top of Sand Hill Rd.,
but I will this weekend.
-tom
<jobst....@stanfordalumni.org> wrote in message
news:Teifb.27116$dk4.8...@typhoon.sonic.net...
>
> I see you still did not perform the shimmy test that I suggested:
<jobst....@stanfordalumni.org> wrote in message
news:yj_eb.26864$dk4.8...@typhoon.sonic.net...
>
> There is an excellent test course for this near your work place on
> Sand Hill road. Ride to the top of Sand Hill and coast eastward
> toward the freeway no-hands with pedals vertical, knees not touching
> the top tube. I don't think speeds over 30 are needed for shimmy on a
> bicycle. If your bicycle shimmies naturally, it will do it on this
> road. If it doesn't, then your shimmy must have been rider induced.
>
Tim McNamara
Shayne Wissler <thal...@nospam.yahoo.com> wrote:
> Hmmm. Neither my front nor my back tires are perfectly round. The
> front rim seems mostly round and true, but the tire itself is off
> by 1-2mm at certain points (Bontrager 700x23 Race X Lite Silica).
> This is the recently installed tire.
All bicycle tires are slightly out of round in my experience and don't
cause dramatic shimmy. In the case of my fiend's bike, the culrit was
that the tire was able to brush against the underside of the crown.
> I don't see anything in the arrogant paragraph claiming that I want
> to write specifications.
Reread it again, and notice that you proclaim the "true" reason for
shimmy and all the steps that bicycle designers "must" take in order
to be competent at their jobs. Pretty arrogant stuff, moreso even
than most of my posts and that takes some doing.
> It's not either/or. I can disagree with Jobst's methods and try to
> understand at the same time.
Perhaps, But your discussion with Jobst betrays little effort at
comprehension and much effort at discrediting him (or anyone who
agrees with him).
> >> >> Perhaps what you mean to say, is that given the current state
> >> >> of the art, it is the rider's *responsibility*, for the sake
> >> >> of his own safety, to be able to respond correctly to shimmy.
> >> >> I agree with that. But saying it that way instead of the
> >> >> way you put it leaves room for designers to have a healthy
> >> >> frustration over the issue and not be complacent about it.
> >> >> It leaves room for a clever engineer with his sights set on
> >> >> the problem to solve it elegantly.
> >> >
> >> > Do it!
> >>
> >> Let's leave your Sunday School lessons out of this; they have
> >> little relevance here.
> >
> > Huh?
>
> Just examine the premises behind his statement. If you don't know
> how to do that then you probably wouldn't appreciate me doing it
> for you.
Dude, at this point I think you're hallucinating. There aren't a lot
of premises behind a two word statement like "do it." Certainly
there's nothing to do with Sunday School lessons. That was just a
bizarre non sequitor on your part.
> >> > I'm waiting for someone, with better insights than I, to solve
> >> > this.
> >>
> >> Well this takes care of one half of my issue with what you've
> >> written. Now if we can just get rid of those hasty
> >> generalizations.
> >
> > Hmmm. "Hasty generalizations?" You're kind of new here, aren't
> > you?
>
> Ad hominem is apparently a favorite technique here. Exactly how
> does being new to the forum impact my ability to discern Jobst's
> propensity for jumping to conclusions?
Because you're just seeing the conclusion and not the many discussions
that have preceeded that conclusion. Those of us who've been
participating in this forum for the past decade or so will naturally
have a different perception of those comments.
> > Jobst can be tetchy and does not suffer fools gladly, but he's
> > been riding bike longer than I've been alive (and I'm 44) and has
> > been an
>
> Unfortunately, age does not always lead one to wisdom. In fact it
> rarely does. So please spare me the age crap.
Youth almost never leads to wisdom, on the other hand, until one has
outlived youth.
> > engineer almost as long as I've been alive. I doubt there's much
> > that's "hasty" about his conclusions, although perhaps you have
> > not seen the chains of events, observations and reasoning that
> > has led to those conclusions.
>
> I see all of the chains that he presents. I've read his FAQ, as
> well as perused his other musings on this topic. So far I'd say
> that he's providing some good practical advice, but that his
> theoretical understanding leaves much to be desired.
Ah, I didn't realize that you were a mechanical engineer! And one
with greater knowledge and experience than Jobst and the other 7 or so
engineers that routinely participate in this forum- or the many of us
that have been riding bike for 30 years or more.
> > A Google search in the archives for "frame shimmy" will reveal
> > much previous discussion- including exactly the kind of vioent
> > shimmy you're deacribing. ISTR that that discussion was within
> > the past two years, it provoked a long thread and much
> > interesting experimentation and discussion.
>
> I've looked through some of the old writings, but perhaps I missed
> some good posts.
Try these:
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&frame=right&rnum=1&t
hl=0,1266642788,1266639808,1266592538,1266525586,1266522966,1266585680,
1266555751,1264932822,1264906985,1264847976,1264323883&seekm=3c612a50.2
4230219%40news.telkomsa.net#link1
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&frame=right&th=15754
447ec7187f2&seekm=DE6M7p.49t%40hpl.hp.com#link1
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&frame=right&th=89501
e6ace86562b&seekm=19981107005131.06764.00000379%40ng138.aol.com#link1
> >> You might consider that with motor vehicles, there's not much
> >> motivation for the elegant solution. Dampeners work, and they
> >> aren't a significant design compromise, so why bother looking
> >> for any better solution? With bikes dampeners are a huge
> >> compromise, so it's a huge mistake to make the comparison you're
> >> making. It only leads to apathy toward the problem.
> >
> > Actually, "dampeners" make things wet. "Dampers" control
> > undesireable movements such as oscillations. A shock absorber is
> > a damper, for example.
>
> How old did you say you were again? You certainly don't act any
> older than a college student.
Young at heart. ;-) Thought you'd appreciate using the right
terminology to make your point. Guess not, eh? That chip on your
shoulder seems to be finely balanced.
> > As far as "apathy to the problem" goes, your description is
> > highly unusual and therefore somewhat suspect as to being
> > something that can be "designed for."
>
> Perhaps there is something wrong with my bike. Perhaps the 1-2mm
> out of round is too much?
As I noted above, all bicycle tires seem to be a little out of round
but this problem is not common (otherwise no one would ride bikes
downhill). I suppose small cross-section with ultra-high inflation
pressures might exaggerate that and would reduce the tires's damping
effect on the oscillation. That might be part of the effect Mike J
noted with his customers, that changing to a wider tire (which usually
also is inflated to a lower pressure) reduces the propensity to shimmy.
Stella Hackell
>
> Since Brandt is stuck in his own dogmatic interpretations of shimmy based on
> his own hacking around on a few bicycles
The fall '03 Jobst-baiting contest is in full swing!
Shayne, if you ask others for scientific proof, you need to supply
some for your own point of view, too. Jobst has been right about
enough things over
enough time to have a lot of credibility here. Insulting and
belittling him
may be entertaining to you, but it doesn't further your argument, and
just
makes you look silly.
Stella
Bill Bushnell
> The big-frame guys often find their shimmy issues solved, or at least
> greatly reduced, by going to wider tires.
Interesting.
On my 62cm (lugged steel) frame road bike I find low- to moderate-speed
"no hands" shimmy is greatly reduced by using _smaller_, narrower tires
(Continental 25mm, vs. Avocet Duro 35mm), although I always experienced
enough shimmy at speeds >15 mph that I never felt comfortable on any of my
road bikes riding no hands with seated, upright torso for more than a few
seconds. In all cases I found that leaning forward and/or putting more
weight on the front wheel, such as putting both hands on or adjacent to
the stem, helped reduce the shimmy.
--
Bill Bushnell
Gordon Renkes
jobst....@stanfordalumni.org wrote:
> Logically one must ask, why now? What are these other riders
> experiencing when "out of the blue" the bicycle becomes unstable?
I experienced an example of this recently. My former road bike
shimmied for the first time in its 13 years of use. It occurred past
the bottom of a fast downhill, on a curve after the road had flattened
out. I had already braked for this curve; I don't remember if I was
still braking when the shimmy started. It did not shimmy while
travelling fast (up to 40 mph) on this descent, nor on descents on the
same road during the previous few weeks, nor on other descents. My
riding partner and I examined the bike before the next climb, because I
had been hearing increasingly louder creaking noises during this ride,
especially on the climb before this descent. I had not heard these
noises the day before, when we were riding hard in the same hilly
terrain. It sounded like the bottom bracket going bad, or worse, the
crank arms coming loose. These were not the problem. My buddy
noticed some "peeling paint". It was actually the metal of the down
tube flaring on either side between the head tube lug and the down tube
shifters. The crack had started at the point of the lug underneath.
The top half of the down tube was still intact. I suppose that crack
may have started before that day, but propogated much farther during
that 20 miles we had ridden. So, we rode, gently for me, on mostly
flat terrain back to the car. I noticed that the frame was much
"flexier" when I did have to go up some gentle rises. I expect that
the smaller out-of-plane bending force constant caused by this crack
made the frame's out-of-plane vibration frequency decrease enough such
that my possible braking or other stimuli caused the vibration to start.
Shayne Wissler
I'm not "baiting". I just object to his presumed omniscience about bicycle
shimmy, and the character attack method by which he peddles his viewpoints.
If he would recognize that there may be some class of shimmy that he hasn't
accounted for, and stop presuming that anyone who experiences anything
different from him is deluded/lying, then I'd have more respect for him.
But when he comes out and calls me deluded--without knowing anything about
me or what happened to me--then he doesn't deserve my respect.
That he knows much I do not dispute, but it's dangerous when people start
presuming they have nothing more to learn so that when they see new
information they brush it aside. It's even more dangerous when acolytes
give experts a god-like status and regard them as infalliable (and if I
look silly to them then I don't care. In fact I'd prefer to look silly to
people who abuse their minds in this way).
I would have a lot more respect for Brandt if he dealt more in facts and
less in character attacks. In his replies to me, he has spent most of his
energies trying to further the view that the rider is at fault in a shimmy,
completely ignoring my particular scenario. I was heartened by a rare,
relevant question he asked in his last reply to me, so much so that I
ignored his other fallacious points and only replied to his question
regarding the difference between the two types of shimmy I've noticed. This
question was exactly on topic. But unless I missed it he's apparently not
interested in the answer to his question.
The cynic in me expects him to either ignore my reply, either by not
responding, or by repeating his "rider is deluded/lying" ad hominem. One
way or the other I just don't think he cares for new information. Someone
like this deserves little respect in their role as an expert.
Shayne Wissler
jobst....@stanfordalumni.org
>> The big-frame guys often find their shimmy issues solved, or at
>> least greatly reduced, by going to wider tires.
> Interesting.
> On my 62cm (lugged steel) frame road bike I find low- to
> moderate-speed "no hands" shimmy is greatly reduced by using
> _smaller_, narrower tires (Continental 25mm, vs. Avocet Duro 35mm),
> although I always experienced enough shimmy at speeds >15 mph that I
> never felt comfortable on any of my road bikes riding no hands with
> seated, upright torso for more than a few seconds. In all cases I
> found that leaning forward and/or putting more weight on the front
> wheel, such as putting both hands on or adjacent to the stem, helped
> reduce the shimmy.
To which I can also say "interesting" because that is one of the tests
I performed. While the bicycle is shimmying (riding no-hands) I
leaned way back, and then leaned forward with my shoulders over the
bars, holding onto the rear of the saddle to keep from sliding off.
Neither position altered shimmy and I believe because the rider's mass
serves only to anchor the saddle so that the shimmy can twist the
frame and bend the fork in its excursions about the rider mass and
rear wheel contact. I suspect a nearly flat rear tire might have the
biggest effect on this. I'll have to try that today.
I think you'll find that the course the front wheel traces while
shimmying is nearly a straight line. Looking over the fork at the
tire contact point, only the top of the head tube (and bars) seem to
be moving from side to side as the wheel steers gyroscopically from
left to right, the trail of the wheel limiting its stroke. I would
like to see a slow motion movie of this event because it is just fast
enough to be seen but not scrutinized while riding.
Jobst Brandt
jobst....@stanfordalumni.org
Shayne Wissler
>> Hmmm. Neither my front nor my back tires are perfectly round. The
>> front rim seems mostly round and true, but the tire itself is off
>> by 1-2mm at certain points (Bontrager 700x23 Race X Lite Silica).
>> This is the recently installed tire.
>
> All bicycle tires are slightly out of round in my experience and don't
> cause dramatic shimmy. In the case of my fiend's bike, the culrit was
> that the tire was able to brush against the underside of the crown.
That's what I suspected. Oh well...
Can the rim itself wobble without wrecking it or knocking it permanently out
of true? Or is its role in this confined to modifying the overall tension
of the system? Because it seems to me that either it was caster motion or
rim instability as the primary component of the shimmy (the rim instability
idea is just a hypothesis). But rims are quite stiff...
>> I don't see anything in the arrogant paragraph claiming that I want
>> to write specifications.
>
> Reread it again, and notice that you proclaim the "true" reason for
> shimmy and all the steps that bicycle designers "must" take in order
> to be competent at their jobs. Pretty arrogant stuff, moreso even
> than most of my posts and that takes some doing.
There was nothing arrogant in what I said, and you misread it. I'm an
engineer myself, so I know what the proper goals of engineering are. It's
not arrogant for me to iterate them to you.
>> It's not either/or. I can disagree with Jobst's methods and try to
>> understand at the same time.
>
> Perhaps, But your discussion with Jobst betrays little effort at
> comprehension and much effort at discrediting him (or anyone who
> agrees with him).
I have no goal of discrediting him. In fact if I didn't meet him in this
manner I'm sure I'd like him. I'd probably like him anyway if I met
him--being stubborn is a common attribute among old men who have an
interesting character.
It's some of the things he says and his method that need discrediting. He
has several assumptions of universal knowledge, but when pressed it came
from examining narrow instances, and when he sees exceptions, he bolts to
his ad hominem method of rejecting the instance instead of examining and
possibly reconsidering his previous knowledge.
>> Just examine the premises behind his statement. If you don't know
>> how to do that then you probably wouldn't appreciate me doing it
>> for you.
>
> Dude, at this point I think you're hallucinating. There aren't a lot
> of premises behind a two word statement like "do it."
Dude, there are a lot of premises behind those two words given the context
in which they were said.
> Certainly
> there's nothing to do with Sunday School lessons. That was just a
> bizarre non sequitor on your part.
Instead of consoling yourself, you might try unpacking exactly what was
intended in the two words. It was not merely that he wanted me to do
something. OK, I'll give you a hint: "Well, if you're so smart, then you do
it." That should get you started.
> Because you're just seeing the conclusion and not the many discussions
> that have preceeded that conclusion. Those of us who've been
> participating in this forum for the past decade or so will naturally
> have a different perception of those comments.
Everyone has the same perception. But there are a lot of different
conclusions. For my part, I was there when my bike did this, and to have
Brandt start attacking me instead of asking clarifying questions tells me
all I need to know about his method.
>> Unfortunately, age does not always lead one to wisdom. In fact it
>> rarely does. So please spare me the age crap.
>
> Youth almost never leads to wisdom, on the other hand, until one has
> outlived youth.
I've met too many old fools to care about issues of age. If someone behaves
wisely, then they earn my respect that way. Being an old bearded man with
lots of "experience" means nothing by itself.
>> I see all of the chains that he presents. I've read his FAQ, as
>> well as perused his other musings on this topic. So far I'd say
>> that he's providing some good practical advice, but that his
>> theoretical understanding leaves much to be desired.
>
> Ah, I didn't realize that you were a mechanical engineer! And one
I have 2 degrees in electrical engineering and know enough about the basic
principles involved in this issue to see that the way Brandt is approaching
it leaves some to be desired *if* he wants have the kind of certainty about
the subject he claims to have.
> with greater knowledge and experience than Jobst and the other 7 or so
> engineers that routinely participate in this forum- or the many of us
> that have been riding bike for 30 years or more.
Brandt has made claims of certainty about some issues here. I ask him where
he gets this certainty. His response is to talk about a few bikes, or to
insult me. I don't need to have a PhD in mechanical engineering to figure
out what's going on here.
>> I've looked through some of the old writings, but perhaps I missed
>> some good posts.
>
> Try these:
Thanks.
Shayne Wissler
jobst....@stanfordalumni.org
(2nd edition)
>> The big-frame guys often find their shimmy issues solved, or at
>> least greatly reduced, by going to wider tires.
> Interesting.
> On my 62cm (lugged steel) frame road bike I find low- to
> moderate-speed "no hands" shimmy is greatly reduced by using
> _smaller_, narrower tires (Continental 25mm, vs. Avocet Duro 35mm),
> although I always experienced enough shimmy at speeds >15 mph that I
> never felt comfortable on any of my road bikes riding no hands with
> seated, upright torso for more than a few seconds. In all cases I
> found that leaning forward and/or putting more weight on the front
> wheel, such as putting both hands on or adjacent to the stem, helped
> reduce the shimmy.
To which I can also say "interesting" because that is one of the tests
I performed. While the bicycle is shimmying (riding no-hands) I
leaned way back, and then leaned forward with my shoulders over the
bars, holding onto the rear of the saddle to keep from sliding off.
Neither position altered shimmy and I believe because the rider's mass
serves only to anchor the saddle so that the shimmy can twist the
frame and bend the fork in its excursions about the rider mass and
rear wheel contact. I suspect a nearly flat rear tire might have the
biggest effect on this. I'll have to try that today.
As you may recall from the FAQ, unloading the saddle is one of the
surest ways to stop shimmy because the rider's mass on the saddle is
the anchor for the oscillations. Without that the frame tubes are
infinitely stiff against the remaining masses involved. You may have
lightened your contact with the saddle.
Tim McNamara
Shayne Wissler <thal...@nospam.yahoo.com> wrote:
> Tim McNamara wrote:
>
> >> Hmmm. Neither my front nor my back tires are perfectly round.
> >> The front rim seems mostly round and true, but the tire itself
> >> is off by 1-2mm at certain points (Bontrager 700x23 Race X Lite
> >> Silica). This is the recently installed tire.
> >
> > All bicycle tires are slightly out of round in my experience and
> > don't cause dramatic shimmy. In the case of my fiend's bike, the
> > culrit was that the tire was able to brush against the underside
> > of the crown.
>
> That's what I suspected. Oh well...
>
> Can the rim itself wobble without wrecking it or knocking it
> permanently out of true? Or is its role in this confined to
> modifying the overall tension of the system? Because it seems to me
> that either it was caster motion or rim instability as the primary
> component of the shimmy (the rim instability idea is just a
> hypothesis). But rims are quite stiff...
Do you mean "can the wheel go temporarily out of true" under some kind
of stress, causing the bike to shimmy violently? Caster motion seems
far more likely, if for no other reason than a small arc of rotation
in the headset being the line of least resistance. As the frame whips
back and forth, the steerer rotates in the headset through a small arc
and return. The tire proceeds in a straight line on the ground while
the headest can be whipping back and forth a few inches.
Of course, if you looked down you'd likely have some optical illusion
of the fork, frame or wheel bending, just like you can produce by
holding a pencil lightly between the finger and thumb and shaking it
up and down. It appears to curve, even though it is not doing so.
John Dacey
wrote:
>I think you'll find that the course the front wheel traces while
>shimmying is nearly a straight line. Looking over the fork at the
>tire contact point, only the top of the head tube (and bars) seem to
>be moving from side to side as the wheel steers gyroscopically from
>left to right, the trail of the wheel limiting its stroke.
So, if we increase a bike's trail, can we assume there will be a
reduction in the severity of the shimmy? Will the converse be true?
> I would
>like to see a slow motion movie of this event because it is just fast
>enough to be seen but not scrutinized while riding.
-------------------------------
John Dacey
Business Cycles, Miami, Florida
Now in our twenty-first year.
Our catalog of track equipment: eighth year online.
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