front wheel wobble
DChin1154
Omega rim on DA hub.Occurs at 35+ mph and is worsened by braking(front). Frame,
fork and headset have been checked and are fine.
Jobst Brandt
You might find this item from the FAQ informative:
-----------------------------------------------------------------------
Subject: 8.60 Shimmy or Speed Wobble
From: Jobst Brandt <jbr...@hpl.hp.com>
Shimmy is not related to frame alignment or loose bearings as is often
suggested. Shimmy arises from the dynamics of forward motion and the
elasticity of the frame, fork, and wheels, and the saddle position.
Both perfectly aligned bicycles and ones with wheels out of plane to
one another shimmy nearly equally well. The same is true for bearing
adjustment. In fact shimmy is more likely with properly adjusted
bearings than loose ones. The bearing or alignment concept is usually
offered as a cause of shimmy and each airing perpetuates the idea.
Shimmy, the lateral oscillation at the head tube, depends primarily on
the frame and its geometry. The inflation of the tire and the
gyroscopic effects of the front wheel make it largely speed dependent.
It cannot be fixed by adjustments because it is inherent to the
geometry and elasticity of the components. The longer the frame and
the higher the saddle, the greater the tendency to shimmy, other
things being equal. Weight distribution also has no effect on shimmy
although where that weight contacts the frame does.
In contrast to common knowledge, a well aligned frame shimmies more
easily than a crooked one because it rides straight and without bias.
The bias force of a crooked frame impedes shimmy slightly. Because
many riders never ride no-hands downhill, or at least not in the
critical speed range, they seldom encounter shimmy. When it occurs
with the hands on the bars it is unusual and especially disconcerting.
There is a preferred speed at which shimmy initiates when coasting
no-hands on a smooth road and it should occur every time when in that
critical speed range. Although it usually does not initiate at higher
speed, it can.
Pedaling or rough road interferes with shimmy on a bicycle that isn't
highly susceptible. When coasting, laying one leg against the top
tube is the most common way to inhibit it. Interestingly, compliant
tread of knobby tires give such high lateral damping that most
bicycles equipped with knobbies do not shimmy.
Shimmy is caused by the gyroscopic force of the front wheel that acts
at 90 degrees to the axis of the steering motion. The wheel steers to
the left about a vertical axis when it is leaned to the left about a
horizontal axis. When the wheel leans to the one side, gyroscopic
force steers it toward that side, however, the steering action
immediately reverses the lean of the wheel as the tire contact point
acts on the trail of the fork caster to reverse the steering motion.
The shimmy oscillates at a rate that the rider's mass on the saddle
cannot follow, causing the top and down tubes to act as springs that
store the energy that initiates the return swing. The shimmy will
stop if the rider unloads the saddle, because the mass of the rider is
the anchor about which the oscillation operates. Without this anchor
no energy is stored. The fork and wheels may store some energy,
although it appears the frame acts as the principal spring.
Shimmy can also be initiated with the hands firmly on the bars by
shivering, typically in cold weather. The frequency of human
shivering is about the same as that of a typical bicycle frame.
------------------------------
Adam Rice
Brandt) wrote:
>
>> Any ideas re: high speed front wheel wobble on road bike? De rosa
>> frame, Campy Omega rim on DA hub.Occurs at 35+ mph and is worsened
>> by braking(front). Frame, fork and headset have been checked and are
>> fine.
>
>You might find this item from the FAQ informative:
>-----------------------------------------------------------------------
>Subject: 8.60 Shimmy or Speed Wobble
>From: Jobst Brandt <jbr...@hpl.hp.com>
>
>Shimmy is not related to frame alignment or loose bearings as is often
>suggested. Shimmy arises from the dynamics of forward motion and the
>elasticity of the frame, fork, and wheels, and the saddle position.
>Both perfectly aligned bicycles and ones with wheels out of plane to
>one another shimmy nearly equally well. The same is true for bearing
>adjustment. In fact shimmy is more likely with properly adjusted
>bearings than loose ones. The bearing or alignment concept is usually
>offered as a cause of shimmy and each airing perpetuates the idea.
[snip]
This might not be a whole-bike shimmy. There's an article at
www.bsn.com/Cycling/ on techniques for balancing your wheels, which might
eliminate this effect. Seems like a lot of trouble to me, but if it works
for you, great.
Adam Rice | adam...@crossroads.net | Check out
Austin TX USA | http://www.crossroads.net | XJ: Translation Jobs
Ted Quade
reported in the cycling community is front wheel imbalance. It will
spawn
oscillation with a period 2x the rotatation speed of the wheel. The
front wheel will tend to straighten out twice per revolution, once
when the heavy spot is to the front of the wheel and once when it
is to the rear.
For example:
36kph
2m wheel diameter
36,000 m/h / 3600 sec/h = 10m/s
10m/s / 2m = 5rps
2 straightens / s * 5 rps = 10hz
So a typical 700c wheel / tyre combination will oscillate at 10 hz
when traveling at 36kph. At twice the speed, the frequescy will be 20hz.
I have found that if the wheel is balancing, much as is done for
automotive
wheels, the propensity to oscillate is significantly reduced and the
amplitude when it does is also significantly reduced. I came upon the
analysis and solution as a result of my own experience.
I built up a set of wheels using Aerohead Velocity Deep V rims. They are
very robust but have what seems to be a 1oz joint plug that causes
quite an imbalance. I balanced the wheel with lead fishing sinkers
attached to the spokes near the rim.
Before balancing, the handling was rather twitchy on downhill decents.
After balancing it runs smooth as silk.
Ted Quade
Jobst Brandt wrote:
>
> D (who?) Chin writes:
>
> > Any ideas re: high speed front wheel wobble on road bike? De rosa
> > frame, Campy Omega rim on DA hub.Occurs at 35+ mph and is worsened
> > by braking(front). Frame, fork and headset have been checked and are
> > fine.
>
> You might find this item from the FAQ informative:
> -----------------------------------------------------------------------
> Subject: 8.60 Shimmy or Speed Wobble
> From: Jobst Brandt <jbr...@hpl.hp.com>
>
> Shimmy is not related to frame alignment or loose bearings as is often
> suggested. Shimmy arises from the dynamics of forward motion and the
> elasticity of the frame, fork, and wheels, and the saddle position.
> Both perfectly aligned bicycles and ones with wheels out of plane to
> one another shimmy nearly equally well. The same is true for bearing
> adjustment. In fact shimmy is more likely with properly adjusted
> bearings than loose ones. The bearing or alignment concept is usually
> offered as a cause of shimmy and each airing perpetuates the idea.
>
John Everett
says...
>
>Any ideas re: high speed front wheel wobble on road bike? De rosa frame,
Camp
>y
>Omega rim on DA hub.Occurs at 35+ mph and is worsened by braking(front).
Frame
>,
>fork and headset have been checked and are fine.
I believe this is covered in the FAQ, but basically it wobbles because it's
a bike. Next time, clamp the top tube firmly between your knees. If it still
wobbles, lift your butt off the saddle. This should make the wobble go away.
--
jeve...@wwa.DEFEAT.UCE.BOTS.com (John Everett) http://www.wwa.com/~jeverett
^^^^^^^^^^^^^^^
Things have gotten so bad I feel the need to disguise my email address.
And I don't like this explanation because I just hate long signatures.
Jobst Brandt
> This might not be a whole-bike shimmy. There's an article at
> www.bsn.com/Cycling/ on techniques for balancing your wheels, which
> might eliminate this effect. Seems like a lot of trouble to me, but
> if it works for you, great.
Might? Why would balancing affect something that is not related in
frequency of wheel revolution. Unless you can feel any instability
from balance (vertical oscillation), how do you explain that balance
would affect shimmy? My bicycle shimmies nicely when I let it but it
goes steady as can be at speeds higher than most bicyclists choose to
coast down hills if I don't let it shimmy. Your suggestion sounds
like the old saw of getting the frame aligned to me.
Jobst Brandt <jbr...@hpl.hp.com>
Adam Rice
Brandt) wrote:
I was *not* suggesting that wheel balancing would affect shimmy. I was
trying to distinguish between two different problems.
The original poster was not clear whether he was observing the kind of
shimmy that makes the frame vibrate enough to be scary (which I always
think of as frame shimmy), or just the annoying lunging sensation from an
imbalanced wheel--I would not describe that sensation as "instability,"
but it is noticeable, and feels as if the wheel is out of round. Anyhow,
that is why I hedged and said "might."
It hadn't occurred to me before that the lunging caused by an imbalalanced
wheel might precipitate shimmy, and your FAQ entry on shimmy does not
address the relationship, or lack thereof. But now that you mention it
(and I admit to getting out of my depth here, which is why I am asking),
isn't it possible that an imbalanced wheel would aggravate shimmy?
Jobst Brandt
> The original poster was not clear whether he was observing the kind
> of shimmy that makes the frame vibrate enough to be scary (which I
> always think of as frame shimmy), or just the annoying lunging
> sensation from an imbalanced wheel--I would not describe that
> sensation as "instability," but it is noticeable, and feels as if
> the wheel is out of round. Anyhow, that is why I hedged and said
> "might."
I don't believe anybody except the princes of "the princes and the
pea" ever felt wheel imbalance while riding. Such inertial forces
only get larger with speed and I can assure you that at speeds over 50
mph on a smooth road (the only place where one might want to coast
that fast) there is no perceptible effect from the imbalance that is
characteristic of bicycle wheels can be felt.
> It hadn't occurred to me before that the lunging caused by an
> imbalanced wheel might precipitate shimmy, and your FAQ entry on
> shimmy does not address the relationship, or lack thereof. But now
> that you mention it (and I admit to getting out of my depth here,
> which is why I am asking), isn't it possible that an imbalanced
> wheel would aggravate shimmy?
The reason it doesn't is because this effect is only theoretical, it
being insignificantly small to the rider's perception. Whether it
has anything to do with shimmy has yet to be shown.
Jobst Brandt <jbr...@hpl.hp.com>
Frank Paysen
Rice) wrote:
>It hadn't occurred to me before that the lunging caused by an imbalalanced
>wheel might precipitate shimmy, and your FAQ entry on shimmy does not
>address the relationship, or lack thereof. But now that you mention it
>(and I admit to getting out of my depth here, which is why I am asking),
>isn't it possible that an imbalanced wheel would aggravate shimmy?
The idea occured to me as well,
The shimmy that Jobst describes is a matter of "eigen-" ("inherent"?)
frequency resonance causing a vibration, aggravated by e.g. human
shivering as the FAQ states, or I assume brick bike paths and the
like could, dependant on velocity, also coincide with this frequency.
I don't know what frequency range we're talking exactly. But assuming
a cadence of 100 rpm and say a 52x12 transmission to be generous, we
would have a resulting frequency of 12 or 13 Hz. I repeat that I don't
know what frequency range we are talking about. IF the frequencies
coincide or are low multiples of each other, and speed is held
constant enough that the aggrevation remains in phase, then it seems
to me this might work. I rather doubt that one could keep it up for
long, though.
Frank
Jobst Brandt
> The shimmy that Jobst describes is a matter of "eigen-" ("inherent"?)
> frequency resonance causing a vibration, aggravated by e.g. human
> shivering as the FAQ states, or I assume brick bike paths and the
> like could, dependant on velocity, also coincide with this frequency.
Also known as resonant frequency that is not dependent on speed of
travel but rather the elasticity and mass of the components.
> I don't know what frequency range we're talking exactly. But
> assuming a cadence of 100 rpm and say a 52x12 transmission to be
> generous, we would have a resulting frequency of 12 or 13 Hz. I
> repeat that I don't know what frequency range we are talking about.
> IF the frequencies coincide or are low multiples of each other, and
> speed is held constant enough that the aggrevation remains in phase,
> then it seems to me this might work. I rather doubt that one could
> keep it up for long, though.
Contrary to what you propose, pedaling or rough road interferes with
shimmy rather than enhancing it. Shimmy occurs best on smooth road
with the rider essentially an inert mass on the saddle with feet on
the pedals. You will note that the damping of the feet on the pedals
has a different effect whether the cranks are horizontal or vertical.
Shimmy, once started, does not go away or change frequency as the
bicycle accelerates down a slope.
Jobst Brandt <jbr...@hpl.hp.com>
Frank Paysen
>Frank Paysen writes:
>
>> The shimmy that Jobst describes is a matter of "eigen-" ("inherent"?)
>> frequency resonance causing a vibration, aggravated by e.g. human
>> shivering as the FAQ states, or I assume brick bike paths and the
>> like could, dependant on velocity, also coincide with this frequency.
>
>Also known as resonant frequency that is not dependent on speed of
>travel but rather the elasticity and mass of the components.
the bricks is dependent on velocity, however. At certain speeds
(frequencies) these vibration will acheive a very violent amplitude,
especially if one is following a crack, causing the entire frame to
shiver and making it difficult to keep a good grip on the handlebars.
By accelerating a bit, the bike will calm down again, even though one
still feels like one is sitting on a vibrator. I won't say this has
anything to do with the shimmy we've been talking about. It may be
another phenomenon altogether.
>
>Contrary to what you propose, pedaling or rough road interferes with
>shimmy rather than enhancing it. Shimmy occurs best on smooth road
>with the rider essentially an inert mass on the saddle with feet on
>the pedals.
>
irregular, and therefore cannot function as aggravator to feed energy
into the vibration. The argument had been about the imbalance of a
wheel spinning at precisely the correct frequency feeding the
vibration (I failed to state this explicitly in my posting, which was
a follow-up on the subject. Possibly this caused a misunderstanding.)
My thought was that in theory this could very well happen, but in
practice would be very unlikely because it would require not only
holding the frequency of the aggravation constant, but also keeping it
in phase. It's not something I'd bet I'd be able to do if I tried.
>You will note that the damping of the feet on the pedals
>has a different effect whether the cranks are horizontal or vertical.
(Interesting...I wonder why this is so...)
>Shimmy, once started, does not go away or change frequency as the
>bicycle accelerates down a slope.
Agreed.
Frank Paysen
wl...@my-dejanews.com
jbr...@hpl.hp.com (Jobst Brandt) wrote:
> Adam Rice writes:
>
> > The original poster was not clear whether he was observing the kind
> > of shimmy that makes the frame vibrate enough to be scary (which I
> > always think of as frame shimmy), or just the annoying lunging
> > sensation from an imbalanced wheel--I would not describe that
> > sensation as "instability," but it is noticeable, and feels as if
> > the wheel is out of round. Anyhow, that is why I hedged and said
> > "might."
>
> I don't believe anybody except the princes of "the princes and the
> pea" ever felt wheel imbalance while riding. Such inertial forces
> only get larger with speed and I can assure you that at speeds over 50
> mph on a smooth road (the only place where one might want to coast
> that fast) there is no perceptible effect from the imbalance that is
> characteristic of bicycle wheels can be felt.
>
> > shimmy does not address the relationship, or lack thereof. But now
> > that you mention it (and I admit to getting out of my depth here,
> > which is why I am asking), isn't it possible that an imbalanced
> > wheel would aggravate shimmy?
>
> being insignificantly small to the rider's perception. Whether it
> has anything to do with shimmy has yet to be shown.
>
> Jobst Brandt <jbr...@hpl.hp.com>
>
Why do you think wheel imbalance cannot be felt? I had a rear wheel to which
I added approximately three grams of weight at one location to balance it.
It was noticeably improved as evidenced by a lot less shaking when spinning
the wheel at high velocity with the bike upside down. Both myself and a
friend did blind testing in which the strip of lead tape that was used was
either placed inside the tire under the tube or not, and we both correctly
and easily determined whether or not the weight was in place by coasting down
a freshly paved hill at 45 MPH.
On automobiles wheels, the addition of only marginally greater weights will
remove vibration that is noticeable at speeds sometimes not much greater than
45 MPH, despite the higher mass of automobile wheels and the intervening
suspension components, including all sorts of bushings which are designed to
isolate the suspension from the frame.
-----------== Posted via Deja News, The Discussion Network ==----------
http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Jobst Brandt
>> I don't believe anybody except the princes of "the princes and the
>> pea" ever felt wheel imbalance while riding. Such inertial forces
>> only get larger with speed and I can assure you that at speeds over
>> 50 mph on a smooth road (the only place where one might want to
>> coast that fast) there is no perceptible effect from the imbalance
>> that is characteristic of bicycle wheels can be felt.
> Why do you think wheel imbalance cannot be felt?
Maybe you didn't read to what you were replying, but the above
paragraph states it fairly clearly. Maybe you haven't done this but
you should before telling the world all about it.
> I had a rear wheel to which I added approximately three grams of
> weight at one location to balance it. It was noticeably improved as
> evidenced by a lot less shaking when spinning the wheel at high
> velocity with the bike upside down.
Nice experiment but no dice. We don't ride upside down bicycles.
> Both myself and a friend did blind testing in which the strip of
> lead tape that was used was either placed inside the tire under the
> tube or not, and we both correctly and easily determined whether or
> not the weight was in place by coasting down a freshly paved hill at
> 45 MPH.
I don't believe a word of it. Where was the lead strip, between the
tire and tube or between the rim and tube? If it was between the tire
and tube (under the tread) you were feeling the lump, not the
imbalance. Beyond that, three grams is about the imbalance of any
conventional wheel. If this were perceptible, do you think
professional racing teams would ride unbalanced wheels?
> On automobiles wheels, the addition of only marginally greater
> weights will remove vibration that is noticeable at speeds sometimes
> not much greater than 45 MPH, despite the higher mass of automobile
> wheels and the intervening suspension components, including all
> sorts of bushings which are designed to isolate the suspension from
> the frame.
I see you are deducing your results from auto tires that are wholly
different from bicycles. If there weren't this difference, then you
would see wheel balancing in the bicycle industry, but you don't.
Your novel discovery of this requirement that apparently no one else
has made is highly presumptuous.
Jobst Brandt <jbr...@hpl.hp.com>
wl...@my-dejanews.com
jbr...@hpl.hp.com (Jobst Brandt) wrote:
>
> > I had a rear wheel to which I added approximately three grams of
> > weight at one location to balance it. It was noticeably improved as
> > evidenced by a lot less shaking when spinning the wheel at high
> > velocity with the bike upside down.
>
> Nice experiment but no dice. We don't ride upside down bicycles.
This was to illustrate that the addition of the weight reduced the imbalance,
which can be perceived when spinning the wheel rapidly while the bike is
upside down. We do ride bicycles in which wheels spin, and this orientation
provides a easy way to observe the effect of wheel imbalance.
>
> > Both myself and a friend did blind testing in which the strip of
> > lead tape that was used was either placed inside the tire under the
> > tube or not, and we both correctly and easily determined whether or
> > not the weight was in place by coasting down a freshly paved hill at
> > 45 MPH.
>
> I don't believe a word of it. Where was the lead strip, between the
> tire and tube or between the rim and tube? If it was between the tire
> and tube (under the tread) you were feeling the lump, not the
> imbalance. Beyond that, three grams is about the imbalance of any
> conventional wheel. If this were perceptible, do you think
> professional racing teams would ride unbalanced wheels?
The lead strip was placed underneath the tube and over the rim strip. The
wheel in question is a DA hub laced 3x with DT spokes to an Open Pro rim.
The rim is true and round to within 0.5 mm. The tube is a Michelin
ultralight, and the tire is a 23c Vredestein Fortezza. Had the lead strip
been placed between the tube and the tire and caused a lump in the tread, any
perceived vibration would have been worse, not better.
The two bikes used are a Look KG196 and a Cannondale CAAD3. The two riders
are 200 and 150 pounds. The road is freshly paved blacktop, about 7%, and we
reach speeds between 43 and 48 MPH.
As to why it is not done in the professional peleton, you yourself have said
that asking a technical question to a professional racer, who may not have
even finished high school, is of dubious value. The fact that they also ride
equipment, such as Spinergy wheel, which you consider a technically poorly
designed or implemented product (or both), seems to illustrate a degree of
indifference that would explain this. In any event, there are other more
significant factors: professionals regularly go through many tires, and any
tire change would require a rebalance, which would be very time consuming
considering the large number of wheels a professional team uses. It is also
more difficult to place a strip of lead on a tubular, unless it were adhered
to the inside edge of the rim, assuming it's not a V-shaped rim. It is
difficult to spin the front wheel rim fast enough to determine the effect of
any placement of a balancing weight, and there is no current machine that I
know of which will spin balance a bicycle wheel.
>
> > On automobiles wheels, the addition of only marginally greater
> > weights will remove vibration that is noticeable at speeds sometimes
> > not much greater than 45 MPH, despite the higher mass of automobile
> > wheels and the intervening suspension components, including all
> > sorts of bushings which are designed to isolate the suspension from
> > the frame.
>
> I see you are deducing your results from auto tires that are wholly
> different from bicycles. If there weren't this difference, then you
> would see wheel balancing in the bicycle industry, but you don't.
> Your novel discovery of this requirement that apparently no one else
> has made is highly presumptuous.
>
> Jobst Brandt <jbr...@hpl.hp.com>
>
I don't see how balancing a wheel is significantly different in an automobile
wheel versus a bicycle wheel. They both spin. In any event, a several gram
weight imbalance on an 18 kg car wheel can be felt at speeds in a car that are
reachable by a bicycle. It is not difficult to imagine that a three gram
weight imbalance on a 1 kg wheel can be felt as well. I'd suggest you or
others actually try it and see if you can notice it. We can easily perceive
this as a significant diminishment in what feels like road graininess, similar
to the effect of riding on concrete versus smooth blacktop.
Jobst Brandt
>>> I had a rear wheel to which I added approximately three grams of
>>> weight at one location to balance it. It was noticeably improved
>>> as evidenced by a lot less shaking when spinning the wheel at high
>>> velocity with the bike upside down.
>> Nice experiment but no dice. We don't ride upside down bicycles.
> This was to illustrate that the addition of the weight reduced the
> imbalance, which can be perceived when spinning the wheel rapidly
> while the bike is upside down. We do ride bicycles in which wheels
> spin, and this orientation provides a easy way to observe the effect
> of wheel imbalance.
You removed a principal constraint by allowing the wheel to spin
freely. In reality the wheel is constrained to roll on the ground
with a tire so hard that its imbalance forces are insignificant
to the compliance of the tire, unlike hat of a car tire that has
about the same compliance and about 40 times the mass. They are
not alike.
>>> Both myself and a friend did blind testing in which the strip of
>>> lead tape that was used was either placed inside the tire under
>>> the tube or not, and we both correctly and easily determined
>>> whether or not the weight was in place by coasting down a freshly
>>> paved hill at 45 MPH.
>> I don't believe a word of it. Where was the lead strip, between
>> the tire and tube or between the rim and tube? If it was between
>> the tire and tube (under the tread) you were feeling the lump, not
>> the imbalance. Beyond that, three grams is about the imbalance of
>> any conventional wheel. If this were perceptible, do you think
>> professional racing teams would ride unbalanced wheels?
> The lead strip was placed underneath the tube and over the rim
> strip. [...] Had the lead strip been placed between the tube and
> the tire and caused a lump in the tread, any perceived vibration
> would have been worse, not better.
The reason I asked is that lead between tube and tire a lump of
stiffer tread would be felt and lead between tube and rim would cause
problems in seating the tire. Both of these conditions have nothing
to do with balance.
> The two riders are 200 and 150 pounds. The road is freshly paved
> blacktop, about 7%, and we reach speeds between 43 and 48 MPH.
That sounds reasonable except that the 150lb rider would not reach
nearly the speed of the 200lb rider, position and clothing being
equal. What differences did you observe on these runs?
> As to why it is not done in the professional peleton, you yourself
> have said that asking a technical question to a professional racer,
> who may not have even finished high school, is of dubious value.
I did not say the racers are not pragmatic, only that they don't
necessarily know why some things are done for technical reasons.
Typical of this was the reason for road and track glue for tubulars.
> The fact that they also ride equipment, such as Spinergy wheel,
> which you consider a technically poorly designed or implemented
> product (or both), seems to illustrate a degree of indifference that
> would explain this.
They get paid to ride the stuff and as long as the manufacturer can
make it work so that it doesn't interfere with their success, they
ride it. The domestiques ride disk wheels and other heavy aero
wheels in hill climbs, and the public eats it up, not knowing that
the ET of these riders does not count at all, so long as they finish
ahead of the broom wagon. You're grasping at straws.
> In any event, there are other more significant factors:
> professionals regularly go through many tires, and any tire change
> would require a re-balance, which would be very time consuming
> considering the large number of wheels a professional team uses.
You ought to see the preparations of team equipment and realize that
wrapping lead wire around spokes is a common way of balancing spoked
wheels for cars and motorcycles.
> It is also more difficult to place a strip of lead on a tubular,
> unless it were adhered to the inside edge of the rim, assuming it's
> not a V-shaped rim. It is difficult to spin the front wheel rim
> fast enough to determine the effect of any placement of a balancing
> weight, and there is no current machine that I know of which will
> spin balance a bicycle wheel.
>>> On automobiles wheels, the addition of only marginally greater
>>> weights will remove vibration that is noticeable at speeds
>>> sometimes not much greater than 45 MPH, despite the higher mass of
>>> automobile wheels and the intervening suspension components,
>>> including all sorts of bushings which are designed to isolate the
>>> suspension from the frame.
>> I see you are deducing your results from auto tires that are wholly
>> different from bicycles. If there weren't this difference, then
>> you would see wheel balancing in the bicycle industry, but you
>> don't. Your novel discovery of this requirement that apparently no
>> one else has made is highly presumptuous.
> I don't see how balancing a wheel is significantly different in an
> automobile wheel versus a bicycle wheel. They both spin.
Maybe if you considered a railway wheel you could see the effect. The
lack of compliance of the tire has a lot to do with it. You may not
recall bias ply car tires, but they has so much damping that balance
wasn't as important then except that those tires had larger
manufacturing irregularities. The permissible imbalance weight of
radial car tires shrunk with the advent of radial tires.
> In any event, a several gram weight imbalance on an 18 kg car wheel
> can be felt at speeds in a car that are reachable by a bicycle. It
> is not difficult to imagine that a three gram weight imbalance on a
> 1 kg wheel can be felt as well. I'd suggest you or others actually
> try it and see if you can notice it.
How about turning that around and trying to feel that there is an
imbalance in a typical bicycle wheel. As I said, I coast often on
highways at speeds over 40mph and can detect no ripple. I am not
convinced of what you seem to feel.
> We can easily perceive this as a significant diminishment in what
> feels like road graininess, similar to the effect of riding on
> concrete versus smooth blacktop.
I don't think so. One is a random rushing sound, the other a rhythmic
once-around. I think the difference can easily be distinguished.
Jobst Brandt <jbr...@hpl.hp.com>
Wayn...@ce9.uscourts.gov
jbr...@hpl.hp.com (Jobst Brandt) wrote:
> wlim writes anonymously:
>
> >>> I had a rear wheel to which I added approximately three grams of
> >>> weight at one location to balance it. It was noticeably improved
> >>> as evidenced by a lot less shaking when spinning the wheel at high
> >>> velocity with the bike upside down.
>
> >> Nice experiment but no dice. We don't ride upside down bicycles.
>
> > This was to illustrate that the addition of the weight reduced the
> > imbalance, which can be perceived when spinning the wheel rapidly
> > while the bike is upside down. We do ride bicycles in which wheels
> > spin, and this orientation provides a easy way to observe the effect
> > of wheel imbalance.
>
> You removed a principal constraint by allowing the wheel to spin
> freely. In reality the wheel is constrained to roll on the ground
> with a tire so hard that its imbalance forces are insignificant
> to the compliance of the tire, unlike hat of a car tire that has
> about the same compliance and about 40 times the mass. They are
> not alike.
Oh, I now understand. You are correct - the compliance of the tire at the
pressures we used, 110-130 PSI, is minimal when compared to the 3 grams of
wheel imbalance. I don't know how to explain this.
>
> >>> Both myself and a friend did blind testing in which the strip of
> >>> lead tape that was used was either placed inside the tire under
> >>> the tube or not, and we both correctly and easily determined
> >>> whether or not the weight was in place by coasting down a freshly
> >>> paved hill at 45 MPH.
>
> >> I don't believe a word of it. Where was the lead strip, between
> >> the tire and tube or between the rim and tube? If it was between
> >> the tire and tube (under the tread) you were feeling the lump, not
> >> the imbalance. Beyond that, three grams is about the imbalance of
> >> any conventional wheel. If this were perceptible, do you think
> >> professional racing teams would ride unbalanced wheels?
>
> > The lead strip was placed underneath the tube and over the rim
> > strip. [...] Had the lead strip been placed between the tube and
> > the tire and caused a lump in the tread, any perceived vibration
> > would have been worse, not better.
>
> The reason I asked is that lead between tube and tire a lump of
> stiffer tread would be felt and lead between tube and rim would cause
> problems in seating the tire. Both of these conditions have nothing
> to do with balance.
We initially placed the lead strip between the tube and the rim strip because
it was to eventually be stuck to the rim UNDER the rim strip when we found
the spot to best reduce the imbalance. We have a Velox rim strip, and didn't
want to unwrap and rewrap the strip many times. The Fortezza tire used was
very loose - it could be removed in a matter of a couple of seconds with only
moderate thumb pressure and no tools. We checked the seating of the tire by
observing the level of the chafing strip and ensured that it was even all the
way around. We spun the wheel after inflation to make sure as well. The
tire seated evenly according to the chafing strip, and there were no lumps
exceeding 1 mm in the tread. The lead strip itself is very thin, probably a
half mm at most. The strip was about 1 cm wide, and about 2-3 cm long. I
don't know if the placement under the tube but over the strip would cause a
problem, but it might since the Velox is pretty thick as well, but as I said,
the tire seated easily and evenly.
>
> > The two riders are 200 and 150 pounds. The road is freshly paved
> > blacktop, about 7%, and we reach speeds between 43 and 48 MPH.
>
> That sounds reasonable except that the 150lb rider would not reach
> nearly the speed of the 200lb rider, position and clothing being
> equal. What differences did you observe on these runs?
I coasted faster, and recorded the 48 MPH speed. My friend coasted in a more
aerodynamic position to compensate for his lighter weight. We both made sure
to keep our butts on the saddle, since after the first couple of runs, it was
clear that whatever perceived differences there were, were not clearly noticed
at the handlebars but could definitely be felt at the saddle.
>
> > As to why it is not done in the professional peleton, you yourself
> > have said that asking a technical question to a professional racer,
> > who may not have even finished high school, is of dubious value.
>
> I did not say the racers are not pragmatic, only that they don't
> necessarily know why some things are done for technical reasons.
> Typical of this was the reason for road and track glue for tubulars.
>
> > The fact that they also ride equipment, such as Spinergy wheel,
> > which you consider a technically poorly designed or implemented
> > product (or both), seems to illustrate a degree of indifference that
> > would explain this.
>
> They get paid to ride the stuff and as long as the manufacturer can
> make it work so that it doesn't interfere with their success, they
> ride it. The domestiques ride disk wheels and other heavy aero
> wheels in hill climbs, and the public eats it up, not knowing that
> the ET of these riders does not count at all, so long as they finish
> ahead of the broom wagon. You're grasping at straws.
>
But it's not only the domestiques that use this equipment. The contenders do
as well, since they are much more often than not the subject of photos and
live camera shots. That they risk their performance using this equipment is
a testament to either the monetary pressures of their sponsors, their
indifference to riding equipment which may or may not help their performance,
or their belief that the equipment does in fact help.
> > In any event, there are other more significant factors:
> > professionals regularly go through many tires, and any tire change
> > would require a re-balance, which would be very time consuming
> > considering the large number of wheels a professional team uses.
>
> You ought to see the preparations of team equipment and realize that
> wrapping lead wire around spokes is a common way of balancing spoked
> wheels for cars and motorcycles.
I have unfortunately never had the opportunity to view a European
professional race up close. It would be a lifelong dream, and would perhaps
open my eyes to many things which the mainstream press do not report on.
I began driving as bias ply tires were being replaced by radial tires, so I
have no experience with them, nor would I have had the capability to
understand the technology at that time in my life anyway. I do understand
the need to have compliance in the tire to observe small imbalances.
> > In any event, a several gram weight imbalance on an 18 kg car wheel
> > can be felt at speeds in a car that are reachable by a bicycle. It
> > is not difficult to imagine that a three gram weight imbalance on a
> > 1 kg wheel can be felt as well. I'd suggest you or others actually
> > try it and see if you can notice it.
>
> How about turning that around and trying to feel that there is an
> imbalance in a typical bicycle wheel. As I said, I coast often on
> highways at speeds over 40mph and can detect no ripple. I am not
> convinced of what you seem to feel.
>
> > We can easily perceive this as a significant diminishment in what
> > feels like road graininess, similar to the effect of riding on
> > concrete versus smooth blacktop.
>
> I don't think so. One is a random rushing sound, the other a rhythmic
> once-around. I think the difference can easily be distinguished.
>
Considering the compliance of the tire and the amount of imbalanced caused by
our three gram weight, it is difficult to understand what we distinguished.
We each ran the test four times (we got tired riding back UP the hill). One
of us would either place or not place the strip of lead tape while the other
was out of view. When not placed, the lead tape was hidden out of view. We
would fully inflate the tire to the other's preferred pressure, and install
the wheel. The rider would appear, hop on the bike, and immediately head for
the hill, about a half mile away.
We made a chart, and each time after coming back, we would write down whether
or not we thought the weight was in place. Being a creature of habit, my
friend placed the weight two times and did not place it two times. Trying to
fool my friend, I placed it three times and did not place it once. He
expected two placements and two non-placements, and thus doubted himself, but
was sure of what he felt each time. We were eight for eight in guessing.
I can't explain why we felt what we did, but there is a noticeable lessening
of vibration at speed. At lower speeds, the effect is not noticeable.
By the way, we had this routine down because of an argument over whether or
not latex tubes made a difference in feel. I thought they would, my friend
did not. We used the same test protocol for tubes (the stems were hidden by
the stem extender) except that we pumped the tires up to 100 psi, and the
rider would appear and then pump the tire the remaining way to his desired
pressure. We used the same hill, the same rear wheel and tire, and the same
bikes. This was before we tried balancing the wheels, but we were both
unable to distinguish between a latex (Vittoria) and butyl (Michelin
ultralight) tube.
> Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
>> You removed a principal constraint by allowing the wheel to spin
>> freely. In reality the wheel is constrained to roll on the ground
>> with a tire so hard that its imbalance forces are insignificant
>> to the compliance of the tire, unlike hat of a car tire that has
>> about the same compliance and about 40 times the mass. They are
>> not alike.
> Oh, I now understand. You are correct - the compliance of the tire
> at the pressures we used, 110-130 PSI, is minimal when compared to
> the 3 grams of wheel imbalance. I don't know how to explain this.
The point is that car tires bounce completely off the road when used
with imbalance and they do this because they have a low spring rate
compared to their mass. You can estimate that by the rate at which
the two wheel bounce... like a table tennis ball and a basket ball.
The bicycle tire is more like the table tennis ball
>> The reason I asked is that lead between tube and tire a lump of
>> stiffer tread would be felt and lead between tube and rim would
>> cause problems in seating the tire. Both of these conditions have
>> nothing to do with balance.
> The lead strip itself is very thin, probably a half mm at most. The
> strip was about 1 cm wide, and about 2-3 cm long. I don't know if
> the placement under the tube but over the strip would cause a
> problem, but it might since the Velox is pretty thick as well, but
> as I said, the tire seated easily and evenly.
>>> The fact that they also ride equipment, such as Spinergy wheel,
>>> which you consider a technically poorly designed or implemented
>>> product (or both), seems to illustrate a degree of indifference
>>> that would explain this.
>> They get paid to ride the stuff and as long as the manufacturer can
>> make it work so that it doesn't interfere with their success, they
>> ride it. The domestiques ride disk wheels and other heavy aero
>> wheels in hill climbs, and the public eats it up, not knowing that
>> the ET of these riders does not count at all, so long as they
>> finish ahead of the broom wagon. You're grasping at straws.
> But it's not only the domestiques that use this equipment. The
> contenders do as well, since they are much more often than not the
> subject of photos and live camera shots. That they risk their
> performance using this equipment is a testament to either the
> monetary pressures of their sponsors, their indifference to riding
> equipment which may or may not help their performance, or their
> belief that the equipment does in fact help.
In a hill climb in stage races, the leaders whose times count, ride
light weight hill climb wheels, not aerodynamic heavy disks, Spinergy,
or others that have no benefit for climbing at the reduced speeds
common when going up hill. No belief will overcome a heavy bicycles
on a long climb, especially among top riders who know what their
capabilities are.
>>> In any event, there are other more significant factors:
>>> professionals regularly go through many tires, and any tire change
>>> would require a re-balance, which would be very time consuming
>>> considering the large number of wheels a professional team uses.
>> You ought to see the preparations of team equipment and realize that
>> wrapping lead wire around spokes is a common way of balancing spoked
>> wheels for cars and motorcycles.
> I have unfortunately never had the opportunity to view a European
> professional race up close. It would be a lifelong dream, and would
> perhaps open my eyes to many things which the mainstream press do
> not report on.
My point is that if balance were a real consideration, teams would
balance their wheels even if you think it is tedious. There are
easy ways to accomplish this such as sticky backed lead tape, that
is not currently available because there is no demand.
>>> It is also more difficult to place a strip of lead on a tubular,
>>> unless it were adhered to the inside edge of the rim, assuming it's
>>> not a V-shaped rim. It is difficult to spin the front wheel rim
>>> fast enough to determine the effect of any placement of a balancing
>>> weight, and there is no current machine that I know of which will
>>> spin balance a bicycle wheel.
Static balance is all that is needed for a wheel as narrow as that
of a bicyucle and this can be done on a truing stand. Try it.
>>> I don't see how balancing a wheel is significantly different in an
>>> automobile wheel versus a bicycle wheel. They both spin.
>> Maybe if you considered a railway wheel you could see the effect.
>> The lack of compliance of the tire has a lot to do with it. You
>> may not recall bias ply car tires, but they has so much damping
>> that balance wasn't as important then except that those tires had
>> larger manufacturing irregularities. The permissible imbalance
>> weight of radial car tires shrunk with the advent of radial tires.
> I began driving as bias ply tires were being replaced by radial
> tires, so I have no experience with them, nor would I have had the
> capability to understand the technology at that time in my life
> anyway. I do understand the need to have compliance in the tire to
> observe small imbalances.
It's the bounce that makes the tire pick up a resonance. Maybe an
electrical analogy works better for you but an RC circuit with too
much R doesn't resonate. R resistance is damping and bias ply tires
have plenty of that. In fact their energy absorbance is why they are
not used today.
That is what I am curious about. What is it you feel. My bicycle is
dead solid when coasting downhill on the expressway at 35-40mph on my
daily commute. Even at much higher speed, no vibration is noticeable.
The effect if any would be a vertical oscillation that would find a
resonance at about 10Hz. There being no lateral component, no lateral
oscillation would be generated. So what effect changes and if one can
guess wrong 50% of the time, how sure are you of the results?
> By the way, we had this routine down because of an argument over
> whether or not latex tubes made a difference in feel. I thought
> they would, my friend did not. We used the same test protocol for
> tubes (the stems were hidden by the stem extender) except that we
> pumped the tires up to 100 psi, and the rider would appear and then
> pump the tire the remaining way to his desired pressure. We used the
> same hill, the same rear wheel and tire, and the same bikes. This
> was before we tried balancing the wheels, but we were both unable to
> distinguish between a latex (Vittoria) and butyl (Michelin
> ultralight) tube.
Oh that doesn't count. You can hear the difference between a
conventional butyl and latex tube when riding. The latex tube has
less damping of high frequencies. That's an old test that doesn't
even take much care to see the difference. How much rolling
resistance changes with the acoustic difference has not been measured.
Jobst Brandt <jbr...@hpl.hp.com>
Wayn...@ce9.uscourts.gov
jbr...@hpl.hp.com (Jobst Brandt) wrote:
It is hard to estimate the resonance frequency. I don't think there was a
singular resonance frequency. It honestly feels like the ride one gets when
rolling on chip-seal type roads (where they place a layer of gooey tar and
then spray fine gravel on top - this may be specific only to the Pacific
Northwest). There just seems to be generalized roughness or graininess,
during the entire revolution of the wheel.
As far as how sure I was of the results, I'm positive I felt the changes, and
I knew once I had gotten near my terminal velocity whether or not the lead
was in place. This is a VERY smooth road. I may have only been influenced
by the fact that I knew I would be getting the wheel twice with the lead and
twice without, so I was pretty sure of the fourth try, but I was nonetheless
sure then as with the first three. My friend was expecting two with and two
without, since this is his nature. First run had it, second didn't, and
third did. On the fourth run, I placed it as well. He came back looking
confused, because he said it felt like the wheel had the lead in place, but
it couldn't have because I already had put it in there twice. When pressed,
he said it was in there and then was confused because he was sure each time.
> > By the way, we had this routine down because of an argument over
> > whether or not latex tubes made a difference in feel. I thought
> > they would, my friend did not. We used the same test protocol for
> > tubes (the stems were hidden by the stem extender) except that we
> > pumped the tires up to 100 psi, and the rider would appear and then
> > pump the tire the remaining way to his desired pressure. We used the
> > same hill, the same rear wheel and tire, and the same bikes. This
> > was before we tried balancing the wheels, but we were both unable to
> > distinguish between a latex (Vittoria) and butyl (Michelin
> > ultralight) tube.
>
> Oh that doesn't count. You can hear the difference between a
> conventional butyl and latex tube when riding. The latex tube has
> less damping of high frequencies. That's an old test that doesn't
> even take much care to see the difference. How much rolling
> resistance changes with the acoustic difference has not been measured.
>
On the rear wheel, with a fairly loud freehub mechanism, we couldn't hear any
difference. I actually didn't know there was a difference in the sounds they
made, but in any event we couldn't feel nor hear a difference, since the
tubes were close in weight. In your experience, is there a riding difference
that is noticeable?
> Jobst Brandt <jbr...@hpl.hp.com>
>
Thanks for your time in responding. What do you think it might be that we are
feeling, and what tests could we do to confirm that?
Jobst Brandt
>> That is what I am curious about. What is it you feel. My bicycle is
>> dead solid when coasting downhill on the expressway at 35-40mph on my
>> daily commute. Even at much higher speed, no vibration is noticeable.
>> The effect if any would be a vertical oscillation that would find a
>> resonance at about 10Hz. There being no lateral component, no lateral
>> oscillation would be generated. So what effect changes and if one can
>> guess wrong 50% of the time, how sure are you of the results?
> It is hard to estimate the resonance frequency. I don't think there
> was a singular resonance frequency. It honestly feels like the ride
> one gets when rolling on chip-seal type roads (where they place a
> layer of gooey tar and then spray fine gravel on top - this may be
> specific only to the Pacific Northwest). There just seems to be
> generalized roughness or graininess, during the entire revolution of
> the wheel.
I am aware that some bicycles have a greater tendency to shimmy than
others and that this is not only related the frame but also to wheels
and tires. Even shimmy usually occurs at a resonant frequency and not
above or below that, and this frequency is speed related. Typically
my bicycle shimmies at about 22mph and not at all over 23mph.
Coasting on a smooth road at all speeds has never exposed a rhythmic
once-around disturbance except when the tire was damaged. None of my
wheels are balanced.
> As far as how sure I was of the results, I'm positive I felt the
> changes, and I knew once I had gotten near my terminal velocity
> whether or not the lead was in place. This is a VERY smooth road.
> I may have only been influenced by the fact that I knew I would be
> getting the wheel twice with the lead and twice without, so I was
> pretty sure of the fourth try, but I was nonetheless sure then as
> with the first three. My friend was expecting two with and two
> without, since this is his nature. First run had it, second didn't,
> and third did. On the fourth run, I placed it as well. He came
> back looking confused, because he said it felt like the wheel had
> the lead in place, but it couldn't have because I already had put it
> in there twice. When pressed, he said it was in there and then was
> confused because he was sure each time.
I don't think you have enough statistical data to make an assessment.
Besides, you should have a more convenient test procedure, with a car
to take you to the top of the hill so that you can perform more
repetitions without rider fatigue, I am still unclear on what you felt
in comparison between the balanced and unbalanced wheel. I believe
you should make the test on a front wheel, where more can be felt.
Jobst Brandt <jbr...@hpl.hp.com>
Wayn...@ce9.uscourts.gov
jbr...@hpl.hp.com (Jobst Brandt) wrote:
> Wayne Lim writes:
>
> >> That is what I am curious about. What is it you feel. My bicycle is
> >> dead solid when coasting downhill on the expressway at 35-40mph on my
> >> daily commute. Even at much higher speed, no vibration is noticeable.
> >> The effect if any would be a vertical oscillation that would find a
> >> resonance at about 10Hz. There being no lateral component, no lateral
> >> oscillation would be generated. So what effect changes and if one can
> >> guess wrong 50% of the time, how sure are you of the results?
>
> > It is hard to estimate the resonance frequency. I don't think there
> > was a singular resonance frequency. It honestly feels like the ride
> > one gets when rolling on chip-seal type roads (where they place a
> > layer of gooey tar and then spray fine gravel on top - this may be
> > specific only to the Pacific Northwest). There just seems to be
> > generalized roughness or graininess, during the entire revolution of
> > the wheel.
>
> others and that this is not only related the frame but also to wheels
> and tires. Even shimmy usually occurs at a resonant frequency and not
> above or below that, and this frequency is speed related. Typically
> my bicycle shimmies at about 22mph and not at all over 23mph.
> Coasting on a smooth road at all speeds has never exposed a rhythmic
> once-around disturbance except when the tire was damaged. None of my
> wheels are balanced.
Can shimmy originate due to some sort of imbalance or deformity of the rear
wheel?
>
> > As far as how sure I was of the results, I'm positive I felt the
> > changes, and I knew once I had gotten near my terminal velocity
> > whether or not the lead was in place. This is a VERY smooth road.
> > I may have only been influenced by the fact that I knew I would be
> > getting the wheel twice with the lead and twice without, so I was
> > pretty sure of the fourth try, but I was nonetheless sure then as
> > with the first three. My friend was expecting two with and two
> > without, since this is his nature. First run had it, second didn't,
> > and third did. On the fourth run, I placed it as well. He came
> > back looking confused, because he said it felt like the wheel had
> > the lead in place, but it couldn't have because I already had put it
> > in there twice. When pressed, he said it was in there and then was
> > confused because he was sure each time.
>
> I don't think you have enough statistical data to make an assessment.
> Besides, you should have a more convenient test procedure, with a car
> to take you to the top of the hill so that you can perform more
> repetitions without rider fatigue, I am still unclear on what you felt
> in comparison between the balanced and unbalanced wheel. I believe
> you should make the test on a front wheel, where more can be felt.
>
We performed the test with the rear wheel because it was the most out of
balance of all of our wheels.
Would an adequate test be to take a well balanced front wheel and to place a
three gram weight between the tube and rim strip? If so, I think I can
arrange this the next break in our weather.
> Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
> Can shimmy originate due to some sort of imbalance or deformity of
> the rear wheel?
Possibly, but that is not what causes shimmy in most bicycles, since
they all shimmy at some critical speed more or less. Some need to be
pushed into it at that speed by a jolt to the bars while riding
no-hands.
> We performed the test with the rear wheel because it was the most
> out of balance of all of our wheels.
Rear wheels probably have no effect on shimmy unless the wobble or
hump is large. I doubt that rear wheel imbalance has any effect.
> Would an adequate test be to take a well balanced front wheel and to
> place a three gram weight between the tube and rim strip? If so, I
> think I can arrange this the next break in our weather.
Forget about putting the weight inside the tire. Wrap solder around
a spoke. 1/8" solder wire from the local hardware store will do fine.
Jobst Brandt <jbr...@hpl.hp.com>
Tom
(*SNIP!*)
>
> > Would an adequate test be to take a well balanced front wheel and to
> > place a three gram weight between the tube and rim strip? If so, I
> > think I can arrange this the next break in our weather.
>
> Forget about putting the weight inside the tire. Wrap solder around
> a spoke. 1/8" solder wire from the local hardware store will do fine.
>
How can this be a blind test with a big hunk 'o solder hanging off the
outside of the wheel? I was under the impression motivating factors for
this test were, among other things, to see if it were possible to tell if
the wheel was ballanced by ride alone, the rider not knowing wether the
wheel was indeed ballanced or not before the ride.
___
TTTTT OO M M The sixth sick shiek's sixth sheep's sick. |~~~|
T O O MM MM @o o@
T O O M M M So if it is in or if it is on it is as it is, *
T OO M M be it in or on. `-'
Jobst Brandt
>>> Would an adequate test be to take a well balanced front wheel and
>>> to place a three gram weight between the tube and rim strip? If
>>> so, I think I can arrange this the next break in our weather.
>> Forget about putting the weight inside the tire. Wrap solder
>> around a spoke. 1/8" solder wire from the local hardware store
>> will do fine.
> How can this be a blind test with a big hunk 'o solder hanging off
> the outside of the wheel? I was under the impression motivating
> factors for this test were, among other things, to see if it were
> possible to tell if the wheel was ballanced by ride alone, the rider
> not knowing wether the wheel was indeed ballanced or not before the
> ride.
The blind testing is not needed for determining whether a bicycle
rolls stably downhill. Either it does or it doesn't. The blind
testing is a test of human perception of something that is too small
to fell, or nearly so.
Let's get back to reality. Shimmy is a distinct instability, not
something in the realm of opinion.
Jobst Brandt <jbr...@hpl.hp.com>
Wayn...@ce9.uscourts.gov
earlier exchange:
In article <72hqr7$4in$4...@hplms2.hpl.hp.com>,
jbr...@hpl.hp.com (Jobst Brandt) wrote:
> Wayne Lim writes:
>
> >> You removed a principal constraint by allowing the wheel to spin
> >> freely. In reality the wheel is constrained to roll on the ground
> >> with a tire so hard that its imbalance forces are insignificant
> >> to the compliance of the tire, unlike hat of a car tire that has
> >> about the same compliance and about 40 times the mass. They are
> >> not alike.
>
> > Oh, I now understand. You are correct - the compliance of the tire
> > at the pressures we used, 110-130 PSI, is minimal when compared to
> > the 3 grams of wheel imbalance. I don't know how to explain this.
>
> The point is that car tires bounce completely off the road when used
> with imbalance and they do this because they have a low spring rate
> compared to their mass. You can estimate that by the rate at which
> the two wheel bounce... like a table tennis ball and a basket ball.
> The bicycle tire is more like the table tennis ball
>
and
> >>> I don't see how balancing a wheel is significantly different in an
> >>> automobile wheel versus a bicycle wheel. They both spin.
>
> >> Maybe if you considered a railway wheel you could see the effect.
> >> The lack of compliance of the tire has a lot to do with it. You
> >> may not recall bias ply car tires, but they has so much damping
> >> that balance wasn't as important then except that those tires had
> >> larger manufacturing irregularities. The permissible imbalance
> >> weight of radial car tires shrunk with the advent of radial tires.
>
> > I began driving as bias ply tires were being replaced by radial
> > tires, so I have no experience with them, nor would I have had the
> > capability to understand the technology at that time in my life
> > anyway. I do understand the need to have compliance in the tire to
> > observe small imbalances.
>
> It's the bounce that makes the tire pick up a resonance. Maybe an
> electrical analogy works better for you but an RC circuit with too
> much R doesn't resonate. R resistance is damping and bias ply tires
> have plenty of that. In fact their energy absorbance is why they are
> not used today.
>
I just picked up snow tires for my car today, and noticed that one wheel had a
three gram weight on the outer surface as the only weight used to counter
imbalances.
In just pressing the tire surface with my thumb, there's no significant
difference in compliance - if anything the automobile tire is harder to dimple
due to the very thick tread and heavy construction. So, when compliance is
mentioned above, is this the amount of compliance relative to the mass of the
wheel, or is it some absolute measurement of compliance like a spring rate?
Also, if an automobile wheel exhibits vibration due to imbalance and this is
due to the spring rate of the tire, would increasing the inflation pressure of
the car tire delay the onset of imbalance until higher velocities? Does this
have any reasonable association with a bicycle wheel?
I'll perform front wheel testing in the morning, but since I'll be doing it
myself, I'll know whether or not I've imbalanced the wheel, so I'll use a
section of sticky-back lead tape on the inner edge of the rim.
Thanks!
Jobst Brandt
> I just picked up snow tires for my car today, and noticed that one
> wheel had a three gram weight on the outer surface as the only
> weight used to counter imbalances.
> In just pressing the tire surface with my thumb, there's no
> significant difference in compliance - if anything the automobile
> tire is harder to dimple due to the very thick tread and heavy
> construction. So, when compliance is mentioned above, is this the
> amount of compliance relative to the mass of the wheel, or is it
> some absolute measurement of compliance like a spring rate?
If you sit on the tire and bounce on it, I think you'll see that it
has some cushion, at least as much as a bicycle tire. Also if you
take just the wheel and bounce it on the ground, it rebounds much
like a bicycle tire except that it store a lot more energy.
> Also, if an automobile wheel exhibits vibration due to imbalance and
> this is due to the spring rate of the tire, would increasing the
> inflation pressure of the car tire delay the onset of imbalance
> until higher velocities? Does this have any reasonable association
> with a bicycle wheel?
I don't know. I believe increasing pressure enhances bounce while
softening the tire makes the ratio between damping and bounce better
to prevent wheel bounce. There are other factors that enter into this
that are less apparent. The rolling radius of the wheel changes with
bounce and this causes large rotational inertial forces in the course
of one revolution. These forces are the ones that affect steering if
it is a front wheel and they cause local skidding that build the odd
shaped cusps in the tread. None of this occurs on bicycle tires.
> I'll perform front wheel testing in the morning, but since I'll be
> doing it myself, I'll know whether or not I've imbalanced the wheel,
> so I'll use a section of sticky-back lead tape on the inner edge of
> the rim.
As I said, if its magnitude is in the realm of perception, then it's
not a problem.
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
> Even if the wheel/tire pair were rigid and the primary imbalance
> force wasn't enough to lift it off of the ground, the secondary
> force (a rotating moment) could be felt.
...as a fore and aft force that is insignificantly small compared
to the mass of rider and bicycle. If it were a front wheel, the fork
would oscillate fore and aft, but there is no resonance at the
frequencies in question, so no amplitude builds up. Therefore, it
isn't perceptible without measuring instruments.
> On a steering axle, secondary imbalance can be felt as feedback
> through the steering mechanism. (steering wheel shake.) The
> magnitude of transmission depends on the characteristics of the
> mechanism.
Only if it is out of the central plane of rotation and then it
would cause shimmy.
> To picture the phenomena, imagine a wide wheel with a large
> unbalanced mass on the outside rim. As the wheel rotates, the
> acceleration keeping that mass in a circular orbit provides a
> reaction force that is outward from the rim at that point. When the
> mass is at 12 o'clock, the force is upward, trying to lean the wheel
> inward. At 3 and 9 o'clock, it tries to turn the wheel toe-in or
> toe-out, respectively. (if the wheel were on the left front corner.)
> If this mass were balanced by an equivalent mass offset 180 degrees
> to the other side of the wheel, but applied with half on the inside
> rim and half on the outside, you'd eliminate the primary shaking
> force, but not the secondary force (moment) due to imbalance.
I think you switched back to a car. The bicycle wheel has such good
lateral symmetry and even then is so narrow that this does not occur.
I am interested in doing some imbalance experiments on shimmy just the
same. I plan to add imbalance and remove it to see if there is any
change in the propensity to shimmy.
Jobst Brandt <jbr...@hpl.hp.com>
Wayn...@ce9.uscourts.gov
jbr...@hpl.hp.com (Jobst Brandt) wrote:
>
> > Would an adequate test be to take a well balanced front wheel and to
> > place a three gram weight between the tube and rim strip? If so, I
> > think I can arrange this the next break in our weather.
>
> Forget about putting the weight inside the tire. Wrap solder around
> a spoke. 1/8" solder wire from the local hardware store will do fine.
>
>
Jobst, finally had a chance to do this experiment. The Seattle area has had
nearly 11 inches of rain this month - we've had the first fully dry days in
nearly three weeks.
Anyhow, I used a strip of adhesive backed lead tape, weight of approximately
three grams, on a well balanced front wheel consisting of a DA hub, Open Pro
rim, and 32 14-15 spokes 3-crossed. The tires were Vredestein Fortezza
pumped to about 130 PSI with a Michelin ultralight butyl tube. The tire is
mounted very roundly, and the wheel, left to spin down by itself shows one
barely heavy spot at the joint (inspecting the weld on the inside of the rim
shows an ugly, blobby weld). The wheel very, very slowly settles with the
weld down. The wheel is true and round to the point where I can see no
noticeable deviation from absolutely true, and in the current configuration
has maybe 500 miles on it. The bike is a Look KG196, with a carbon-fiber
straight fork.
I made four runs down the hill, with a gradient of somewhere around 7%
probably, reaching a speed of 43 MPH each time. The runs alternated between
with and without the lead tape, applied directly over the joint on the inner
surface of the rim (so it added to the heavy spot).
Each time, through thinly gloved hands, I was able to discern whether or not
the tape was applied. When weighted, there is a vibration that can be felt,
which seems similar to that felt previously at the rear wheel, but which also
seems of less amplitude than I felt previously. The wheel is rotating too
fast for me to determine if the vibration is up/down or forward/backward.
The vibration is not felt through the saddle, and seems dampened considerably
when I lean forward and increase the weight on the wheel (I can see the tire
casing flex at this point). Sitting way back does not seem to increase the
amplitude.
When going down without the tape, there is practically no vibration at all, so
the difference is fairly clear.
I don't know how to calculate the angular momentum or the resulting up/down or
forward/backward component of a 3 gram weight rotating at these speeds, but it
certainly seems likely to have been felt. I don't know why it seems worse on
the rear wheel (a Spinergy wheel) than on a spoked front wheel other than that
the wheel's structure must contribute to the effect. I think if I understand
your previous posts, that leaning on the bars to increase the weight on the
front wheel, and subsequently seeming to feel the vibration get damped, would
indicate that the vibration is imbalance related.
Prior to the test today, I was convinced by your factual arguments and
statements that it must have been something else causing the vibration or that
I had imagined the vibration, and now I'm more confused. I definitely feel
something. Is there any other test which I can perform?