Shimmy, according to BQ

[William]

I am a recent subscriber of Bicycle Quarterly. I had thought about
subscribing for a while, and two things about the newest issue made me
pull the trigger. One was the write up about the Bilenky 650B tandem
(dude, I want one). The other was the article about shimmy. I know
Jan Heine has a reputation under some sections of the big tent of
cycling, and I was interested to hear what he had to say. I expected
by now somebody would have started a thread about the shimmy article,
but it is towards the back. My Samuel Hillborne is the first bike
I've owned that has a pronounced tendency to shimmy when riding no-
handed. I'm not the most experienced rider. I've only had 30 or 40
different bikes in my lifetime, so I don't have nearly the experience
Jan does. I hoped to gain a greater understanding of the problem and
maybe do something about it on my Sam.

Unfortunately, I found the article almost entirely unsatisfying. The
Cliff-notes synopsis is: "I don't know what causes shimmy, nor does
anyone else. Here's what several oldschool guys said about shimmy.
They were wrong. I can't take a bike that doesn't shimmy and change
it into a bike that does shimmy. Even though I don't have any ideas
about the causes or the solutions, you should absolutely swap your
headset to needle bearings if your bike shimmies and hope for the
best, even though I don't know if it will help, and maybe will make it
worse"

Now don't get me wrong. I don't understand shimmy, but I came to the
article with the attitude of student. The only other articles I've
read on the topic are Sheldon Brown's (RIP) very brief glossary
discussion and the Jobst Brandt article. For Jan to put the single
word "Shimmy" on the cover, and to title his article "What Causes
Shimmy?" suggests that he knows something. The article content itself
suggests to me that Jan might not know any more about shimmy than any
of us. That's not necessarily a bad thing: I'm convinced it's a
complex problem. But I'd almost rather see a person in a pedagogical
position of leadership to say "Hey, I know a lot, but I don't
understand shimmy. Here's some anecdotal observations I've made.
Here's some anecdotes I've heard, but haven't verified." and just end
it there.

Since I'm growing convinced that there might not be anyone who really
understands shimmy, I'm going to run some experiments of my own on my
Hillborne to attempt to understand it more. Since that bike, in it's
current state, shimmies willingly when riding no-handed at 15mph on a
smooth flat road, I think I have a decent baseline and reasonably
reproducable test environment. I'm going to try several (numerous?)
things, and I'll at least try to take better than normal notes, and
see if I can learn anything.

[Steve Palincsar]

On Fri, 2010-12-10 at 10:03 -0800, William wrote:
> I expected
> by now somebody would have started a thread about the shimmy article,
> but it is towards the back.

And let's not forget, much of the country has yet to receive the Winter
2010 BQ issue. So please, wait on the discussion until we Right
Coasters have had a chance to read the article!

[Seth Vidal]

+1!

-sv

[Bruce]

Send this part off to Eben Weiss. He can always use good material..

---

From: William <tape...@gmail.com>

[Steve Palincsar]

On Fri, 2010-12-10 at 10:29 -0800, Jan Heine wrote:
> I am beginning to believe that all bikes have a tendency to shimmy,
> and depending on a number of factors, the oscillations either are
> dampened or self-reinforce.

Which is exactly what Jobst Brandt says in the rec.bicycles.tech FAQ.

[newenglandbike]

OK, hoping not to spoil for folks who haven't seen the article yet- I
thought it was a decent survey of plausible causes for shimmy. It
didn't reveal a catch-all cure for the problem, but that's probably b/
c none could possibly exist, since there are so many possible causes,
some of them combining with each other. BTW if you're going to try
the needle-bearing route, I think velo orange has them now(?) whereas
they were getting scarce before. Anyway good luck with sorting out
the on your rivendell.

[William]

Jan

I'm extremely flattered at your almost instant reply. I don't know if
that means you regularly read the list or if somebody you know does.
I admire your work deeply and endorse your publication
enthusiastically. Every copy of BQ I've seen has had something
astonishing for me. This issue was no different. I am pleased to be
a subscriber.

Regarding shimmy, it's possible that my expectations were
unrealistic. I thought I'd learn some conclusive, empirically
testable conclusions, and I didn't get that. That being the state of
things, I'm motivated now to experiment myself. I'm certain that you
encourage that, and your article actually has helped urge me to do
that which I think is a positive outcome.

The things that 100% can agree upon is that shimmy is an oscillation.
For that reason, it is easy to assume that there should be a spring
+mass+damper model that can be used to understand the system.
Whatever that system is, we can also agree, I think, that there exists
some excitation force is acting on that system and making it
oscillate. The missing piece in the few articles I've read prior to
yours is a failure to establish and define what any of these things
even are. What is the spring? You argue that it is the flexing
torsion of the frame, but then concede that both the stiff frames you
hate nor the flexy frames you love both don't shimmy. You imply that
tire flex has something to do with the system, but it's not clear to
me whether you think it's part of the spring, the mass, the damper,
the exitation force, a combination, or all four. What is the mass?
Some suggest that it is only the steering parts, others state it is
everything including rider and the rear part of the bike. What's the
damper? You argue that it's the stuff that hinders rotation: headset
plus riders hands, and indirectly the riders leg squeezing the top
tube. J. Brandt says tire tread is also a significant damper.
Regarding the excitation force, there is no consensus of what it is or
where it comes from. Sheldon(RIP) said it came from the back end of
the bike, J. Brandt says it comes from the spinning wheel and
sometimes from the natural frequency of human shivering. You, I
think, allow it to be anything, since it is the amplifying or
attenuating property of the system that is important, hence the
artificial whacking the top tube to get it going. If there isn't even
consensus on what the system is, then there is no hope to formally
construct a comprehensive understanding of that system.

It very well may be that shimmy is just a property of a bike+rider
system that is the unknown functional combination of numerous
unmeasurable variables. If that's the real answer, then maybe you're
recommendation is the only one that works:

If your bike shimmies, change something
If it got better, be happy or change the same thing even more
If it got worse, change the same thing in the other direction
If it stayed the same, change something else

Again, my opinions about whether or not your article not meets my
expectations does not reflect on the quality of your contributions to
the cycling world. I hoped that your article starts a dialogue that
gets the topic driven to a more satisfying scientific understanding.
It all strikes me as voodoo right now. With all due respect, this
needle bearing headset thing, especially, strikes me as voodoo.

Bill


On Dec 10, 10:29 am, Jan Heine <hein...@earthlink.net> wrote:
> William,
>
> I am sorry you are disappointed with our article on shimmy. We tried
> to offer summary of the factors that appear to cause or exacerbate
> shimmy. After all, we know that some bikes rarely shimmy (heavy tubes,
> long trail, no load, skinny tires). It appears that shimmy is a multi-
> faceted problem with more than one cause and more than one solution.
> To provide a complete picture, we presented other opinions on the
> issue, which may help you in your own research... I find it
> fascinating what people thought about these things 50 or 70 years ago.
>
> Most of all, we felt the need to publish this article, because we very
> much like bikes with optimized handling, wide supple tires, relatively
> flexible tubing, etc. The one downside of these bikes is a greater
> tendency to display shimmy. Of course, your Sam Hillborne shows that
> even bikes that are very different also can display persistent shimmy.
> And none of our favorite bikes shimmies a lot, so low trail, front
> loads, wide supple tires and relatively flexible tubing don't
> automatically result in a bike that shimmies. I am beginning to

> believe that all bikes have a tendency to shimmy, and depending on a
> number of factors, the oscillations either are dampened or self-
> reinforce.
>

> For your bike, if you don't already have a needle-bearing headset, I'd
> give it a try. That is the only thing we have found to work
> consistently in "curing" shimmy or at least reducing it so that it
> appears only rarely. You may also try to switch to narrow, stiff
> tires, but there are downsides to that. If you are carrying a load on
> your bike, you could try using a backpack (with its own downsides).
> It's hard to change the tubing or geometry of your bike...
>
> I don't know what you expected in the article, but I would like to
> remind you that we offer a money-back guarantee for the unused portion
> of your subscription. And if your experiments yield something
> conclusive, please let us know. We'd love to publish your experiences
> as an additional piece to the puzzle.
>
> Jan Heine
> Editor
> Bicycle Quarterlyhttp://www.bikequarterly.com
>
> Follow our blog athttp://janheine.wordpress.com/

[Steve Palincsar]

The VO 1" threaded roller bearing headset is in fact in stock right now,
$36.
http://store.velo-orange.com/index.php/components/headsets/vo-roller-bearing-headset-1-threaded.html

[Allan in Portland]

BTW, there's the Bicycle Quarterly Reader's Review list,
http://groups.google.com/group/bqrr , that was created as a venue for
precisely these types of discussions.

Not saying you can't discuss the mag anywhere you please, just saying
we'd really appreciate the discussion there. :-)

Carry on,
-Allan

[Tim McNamara]

Shimmy appears to be one of many properties of bicycles that is not
well understood. The math involved to describe what bikes do is very
complicated- even just turning a corner is hard to describe
mathematically because the bike describes arc in two different
planes- and fortunately we don't need to do the math in order to be
able to *ride* bikes! Shimmy is something that plagues bicycles,
motorcycles and shopping carts. Shimmy in cars and trucks is usually
due to an out of balance wheel bouncing up and down and is a
different beast, as I understand it.

From what I've read, shimmy is caused by the bike frame acting as a
spring. The head tube whips back and forth, causing some rotation of
the steerer in the headset. There is probably a contribution by the
steering geometry and from the forces of the spinning wheel,
especially the front wheel. As the frame whips to the left, it "runs
into" the gyroscopic force of the wheel and then whips to the right;
rinse and repeat. The mass of the handlebars, brake levers, etc.
will also contribute. Most people find that shimmy is speed-
dependent. A stiffer frame is probably likely to shimmy less. My
guess is that a bike with a more lightly loaded front end is more
likely to shimmy (short chain stays, long top tube). A lighter, more
responsive bike may be more prone to shimmy (but I don't know that
this is really the case). Larger frames may be more likely to shimmy
than smaller frames.

A shimmy has several fulcrum points: the contact patch of the front
wheel, the rider on the saddle and the contact patch of the rear
wheel; possibly also the rider's feet on the pedals. The rider's
hands on the bars tend to stop a light shimmy, but a rider who is
cold and shivering can induce shimmy through his or her hands. There
is a natural tremor in all people which can induce shimmy
(photographers are very aware of this tremor which causes blurring at
shutter speeds below 1/60 or 1/30)

IME the fastest way to stop a shimmy is to lift my weight off the
saddle. This has always stopped a shimmy cold. I don't have to
stand all the way up, just ease the weight up until the shimmy stops.

Preventing shimmy seems to be a black art. I have a friend who's Al
De Rosa shimmied horribly on descents; it went away when re put on a
new front tire. No idea why, it was the same make and model tire.
Wider tires at lower pressure may offer more damping and reduce
shimmy. A steering damper may do the same. Jan has reported that
needle bearing headsets reduce shimmy; I haven't tried switching
headsets. Changing weight distribution (shorter or longer stem, any
bags and such on the bike, moving the saddle slightly forward, etc.)
may reduce or worsen shimmy.

[William]

Allan, thanks for that suggestion.

On Dec 10, 11:10 am, Allan in Portland <allan_f...@aracnet.com> wrote:
> BTW, there's the Bicycle Quarterly Reader's Review list,http://groups.google.com/group/bqrr, that was created as a venue for

[stevep33]

The shimmy article was OK. In general, I'm not a fan of every BQ
article I read, but BQ is the only publication I read cover to cover
every time.

FWIW the two fender articles alone make buying a copy worthwhile.

[Michael_S]

Funny, Bill, that you say your Hillborne shimmied. The one I had (now
sold) was the most stable bike I've ever ridden with no hands in my
life. I could have had a 3 course dinner while riding and not even
think about touching the bars. I had the standard Riv supplied Tange
headset and even with Schwalbe Smart Sams ( a knobbie tire) it was
smooth as glass. The replacement bike, a used Ram, is not as stable,
but is more like other bikes I've had. Neither bike has any shimmy at
all. I did own, for a while, a Cotic Roadrat , but that baby was
shimmy city and was sold quickly. On that bike a headset change
quieted it as did a tire switch. But I could not get rid of it.

I even think the size and shape of the rider could influence it
dynamically as much as bike geometry and even things like tire tread
pattern.
As others have mentioned above, shimmy is a complex set of factors,
and due to system (bike/rider) to system variation it can affect one
of identical bikes and not the other.

~Mike~

> > -Allan- Hide quoted text -
>
> - Show quoted text -

[Allan in Portland]

> Allan, thanks for that suggestion.

Sure. And to clarify, since your a new sub and may not realize, it's
the _Reader's_ list. Jan is also on the list and probably monitors it,
much as he does here and elsewhere, but it is of the Reader's. There
is no party line and polite criticism, is certainly free to post.

Regards,
-Allan

[William]

Mike

This is part of the voodoo feel to the whole thing. You can find an
article that says knobbies damp out shimmy. You can find another that
says knobbies supply the excitation force for shimmy. You can find
another article that states that wide tires like knobbies are
typically more compliant and therefore enable low frequency
oscillations to be amplified by the system.

My first few experiments are going to be:

1. Baseline the bike. Log initial condition of all independent
variables that I might change. Attempt to measure the frequency and
amplitude of the shimmy
2. Vary front tire pressure and ride. Note changes
3. Vary rear tire pressure and ride. Note changes
4. take reference weight (like maybe two full water bottles) and put
them at various locations on the system and note any changes
A. On front rack
B. In H2O cages
C. In jersey pocket
D. On rear rack
E. maybe elsewhere
5. Change tires
6. Change front wheel
7. Change rear wheel
8. Tighten headset or similarly damp steering
9. Load rear end heavily
10. Load front end heavily

[Montclair BobbyB]

With some exceptions (like life-threatening high-speed wobs, no
thanks)... maybe it's time we just embrace the shimmy... it could just
be our bikes telling us:

Slow the F down...
Put your damn hands back on the bars
Get a trailer if you wanna haul sh**
Turn off that awful music on your iPod, it's giving me the shimmies
Get me some decent tires and a nice headset, you cheapskate
Don't worry about it... It's what makes me ride so nicely at all other
times....

I fully expect to discover a shimmy in my Bomba (at some point)...
I'll try not to freak out...
Happy Friday, everyone... I'm ready to shimmy myself...

Peace,

BB

> > > - Show quoted text -- Hide quoted text -

[MichaelH]

I would suggest adjusting / slash tightening the headset, before I
bought a new one.

My Ebisu All Purpose frame had a very slight front end shimmy as soon
as I put it together. After two years of riding, I became aware that
the shimmy was very gradually getting worse. One day I checked the
headset and discovered it had loosened considerably. I ride a lot of
bad roads and I now suspect that the top nut had never been tightened
enough and rattled loose. It's better now.

Michael

[BPu...@aol.com]

At last, a voice of reason!

 

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[Clayton Scott]

wish I had my BQ already.

[William]

According to Jan and others, the headset is a source of damping
friction. Things that resonate out of control are underdamped. So if
the headset has too little friction, then putting more friction on it
will reduce the amplitude response of the system, all other things
being equal. Higher viscosity grease, high friction sealed bearings,
needle bearings, adjusting it tight, external dampers, all would
increase that. The thing I'm skeptical of is the magnitude of those
frictional forces. They are all tiny. I would think that the
frictional force of the tire sticking to the ground and resisting
steering would be much larger in magnitude than the frictional force
of the headset resisting steering. Like a lot larger. Like 10-100
times larger, I'd bet. I don't have the tools to do that kind of
metrology, so I'm adding to the unsubstantiated speculation, but I
think I can look for the effects on the other end.

[cyclot...@gmail.com]

10:1 he lurks here...

On Dec 10, 10:38 am, Bruce <fullylug...@yahoo.com> wrote:
> Send this part off to Eben Weiss. He can always use good material..
>
> ________________________________

> From: William <tapebu...@gmail.com>

[Michael_S]

just saying that the new issue of BQ is the best yet. And that Bilenky
tandem.... to die for.

I find the older I get the more of a bike geek I've become. Very
scary.

~Mike~



On Dec 10, 3:12 pm, "cyclotour...@gmail.com" <cyclotour...@gmail.com>
wrote:

> > worse"<<- Hide quoted text -

[doug peterson]

Whooee, take off for bike ride & look what I missed! I'll read the
entire thread but for the moment here's some Riv content to chew on:

The Atlantis is arguably one of the most stable bikes made. With my
normal collection of rackage and a moderate sized front bag that'll
hold a few pounds, it's rock solid. By adding panniers in the wrong
places, I can get frightening shimmies. The key is to put the weight
in the right places and it's back to rock solid. This took some
experimentation to sort out and I firmly believe, based on talking to
numerous tourists with similar loads on a variety of bikes, that
personal riding style has a lot to do with it. Playing with the
weight placement is the key to stability.

Another list member had a Hillborne that scared the daylights out of
him when he added the same front bag that I use daily. Remove bag, no
shimmy. Add bag, death wobble. I submit that just these 2 data
points point out the complexity of the issue.

dougP

On Dec 10, 3:12 pm, "cyclotour...@gmail.com" <cyclotour...@gmail.com>
wrote:

[cyclotourist]

Yeah, if I ever get a new tandem, it will probably be a Bilenky similar to that.  For the moment I'm still thinking a Co-Mo Periscope though.

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Cheers,
David
Redlands, CA

...in terms of recreational cycling there are many riders who would probably benefit more from
improving their taste than from improving their performance. - RTMS

[William]

Jan

Again, I appreciate your thoughts, and your massive contributions.
I'll post findings once I have findings to post.

Have a great weekend


On Dec 10, 5:42 pm, Jan Heine <hein...@earthlink.net> wrote:

> On Dec 10, 11:07 am, William <tapebu...@gmail.com> wrote:
>
> > With all due respect, this
> > needle bearing headset thing, especially, strikes me as voodoo.
>

> It may be voodoo, but so far, it's worked in 100% of the cases we've
> tried. Mark's Ti Cycles shimmied terribly once he added a handlebar
> bag, as soon as he took his hands off the bars. With a needle bearing
> headset, it only shimmied at 24-26 mph when pedaling at 90-110 rpm no-
> hands. His Goodrich shimmied less, but still annoyingly so at speeds
> of 18-22 mph no-hands. It doesn't any longer with a needle bearing
> headset. After we published this, a reader also changed their headset,
> and also got rid of their shimmy.
>
> Furthermore, we've never had a test bike with a needle bearing headset
> that had significant shimmy issues, and we've also never had a 650B
> low-trail front-loading test bike with a ball-bearing headset that did
> NOT have shimmy. It seems that Chris King headsets, for all their
> other virtues, are more likely to shimmy.
>
> Furthermore, several people, including myself, have experienced shimmy
> with loose headsets, which went away when the headset was tightened.
> So clearly, headsets CAN be a component that allows shimmy to develop
> or conversely, attenuates it.
>
> So all I am reporting is a trend, and a hypothesis why this may work.
> It may be just chance, and on your bike, it may not work, nor on the
> next 20 bikes we test, and it may turn out a blind alley after all.
> But it's worth a try, as it's inexpensive and easy to do, with no
> downsides at all.
>
> Jan Heine
> Editor
> Seattle WA 98121http://www.bikequarterly.com

[CycloFiend]

on 12/10/10 10:03 AM, William at tape...@gmail.com wrote:
> Since I'm growing convinced that there might not be anyone who really
> understands shimmy, I'm going to run some experiments of my own on my
> Hillborne to attempt to understand it more. Since that bike, in it's
> current state, shimmies willingly when riding no-handed at 15mph on a
> smooth flat road, I think I have a decent baseline and reasonably
> reproducable test environment. I'm going to try several (numerous?)
> things, and I'll at least try to take better than normal notes, and
> see if I can learn anything.

There have been several significant discussions of shimmy on the iBob list
reasonably recently and over the years.

Ride buddy JimG has also documented his shimmy experiences and
expermenting/troubleshooting with a non-Rivendell bicycle via his blog
(which can be found via http://yojimg.net/bike )

There are certainly variables he found to damp or reduce speed-specific
oscillations.

http://sfcyclotouring.blogspot.com/search?q=shimmy

And just to mention too, that a general discussion of BQ articles is
probably best discussed on a more general list.

- Jim

--
Jim Edgar
Cyclo...@earthlink.net

Cyclofiend Bicycle Photo Galleries - http://www.cyclofiend.com
Current Classics - Cross Bikes
Singlespeed - Working Bikes

Gallery updates now appear here - http://cyclofiend.blogspot.com

"Then I sat up, wiped the water out of my eyes, and looked at my bike, and
just like that I knew it was dead"

-- Robert McCammon, "Boy's Life"

[EricP]

Two (hopefully quick) examples from my limited experience in the past
few years. Worst shimmy ever had was on a 1st generation Kogswell
that Esteban now owns. Would even shimmy when riding with both hands
on the bars. A guess - my weight at the time acted to overload the
bike causing the shimmy. Some day would love to ride that bike again
and see if my losing 40 or so pounds from that time makes a
difference.

My Sam Hillborne had some tendency to shimmy in certain occasions.
Even with Marathon Supreme tires. Earlier this summer had Hiawatha
Cyclery install a Shimano 105 headset instead of the one that comes
with the bike. Shimmy has stopped. A number of reasons that could
be. No matter what, am even a happier camper with the bike.

Still waiting for my BQ.

Eric Platt
St. Paul, MN

On Dec 11, 1:13 am, CycloFiend <cyclofi...@earthlink.net> wrote:

> on 12/10/10 10:03 AM, William at tapebu...@gmail.com wrote:
>
> > Since I'm growing convinced that there might not be anyone who really
> > understands shimmy, I'm going to run some experiments of my own on my
> > Hillborne to attempt to understand it more.  Since that bike, in it's
> > current state, shimmies willingly when riding no-handed at 15mph on a
> > smooth flat road, I think I have a decent baseline and reasonably
> > reproducable test environment.  I'm going to try several (numerous?)
> > things, and I'll at least try to take better than normal notes, and
> > see if I can learn anything.
>
> There have been several significant discussions of shimmy on the iBob list
> reasonably recently and  over the years.
>
> Ride buddy JimG has also documented his shimmy experiences and
> expermenting/troubleshooting with a non-Rivendell bicycle via his blog
> (which can be found viahttp://yojimg.net/bike)
>
> There are certainly variables he found to damp or reduce speed-specific
> oscillations.  
>
> http://sfcyclotouring.blogspot.com/search?q=shimmy
>
> And just to mention too, that a general discussion of BQ articles is
> probably best discussed on a more general list.
>
> - Jim
>
> --
> Jim Edgar

> Cyclofi...@earthlink.net
>
> Cyclofiend Bicycle Photo Galleries -http://www.cyclofiend.com

> Current Classics - Cross Bikes
> Singlespeed - Working Bikes
>

> Gallery updates now appear here -http://cyclofiend.blogspot.com

[Bill M.]

I also have a first-generation Kogswell P/R. It shimmied badly with a
5 - 10 pound load in a Wald basket zip-tied to the top of a Blackburn
rear rack. I could feel the weight of the load wagging like a dog's
tail. With the same commuting payload in panniers on the same rack,
no shimmy. There was a small rack trunk containing a couple of pounds
of tubes, tools, granola bars and headlight batteries on a front rack
in either case. The headset is the cheap ball bearing unit that came
with the frame.

My Riv Road has never shimmied, nor have any of my other bikes.

Bill

[Kelly]

I had an experiance with a high speed shimmy .. always over 50 mph and if I was trying to turn it was even worse.  Tried everything.   Giant eventually gave me a new frame .. only because they didn't have a matching fork for the frame I had.. in that case they believed it to be in the frame.  It was pure torture.. I don't like being afraid of my bike, but after having it shimmy/shake at 57 mph in a turn I was afraid of that bike at speed.  Another time at 63 mph.   Headsets, wheels, tires, handle bars, stems.. seat adjustments.. what's worse the only way to test to see if it's fixed was to get back to that speed.  After I got the new frame is was like night and day.. and relaized the bike had been loose  or looser than the new one.. loose = not as stable even in those 30 40 mph turns as the new one..

 

I  trying to say that means anything.. just saying I don't agree that shimmy is part of a bike or that we should have to suck it up.  If a bike shimmy's it takes the fun and love for the bike away.. a deep gut renching saddness that the bike isn't what it should be. 

 

As a consumer a shimmy on a new bike is not acceptable to me.  Period.  I expect the answer to be found... in design or something.

 

Later

 

Kelly

 

 

[hobie]

Shimmy,shimmy,cocoa pop !!!!

On Dec 10, 1:03 pm, William <tapebu...@gmail.com> wrote:
> I am a recent subscriber of Bicycle Quarterly.  I had thought about
> subscribing for a while, and two things about the newest issue made me
> pull the trigger.  One was the write up about the Bilenky 650B tandem
> (dude, I want one).  The other was the article about shimmy.  I know
> Jan Heine has a reputation under some sections of the big tent of
> cycling, and I was interested to hear what he had to say.  I expected
> by now somebody would have started a thread about the shimmy article,
> but it is towards the back.  My Samuel Hillborne is the first bike
> I've owned that has a pronounced tendency to shimmy when riding no-
> handed.  I'm not the most experienced rider.  I've only had 30 or 40
> different bikes in my lifetime, so I don't have nearly the experience
> Jan does.  I hoped to gain a greater understanding of the problem and
> maybe do something about it on my Sam.
>

> Unfortunately, I found the article almost entirely unsatisfying.  The

> Cliff-notes synopsis is: "I don't know what causes shimmy, nor does
> anyone else.  Here's what several oldschool guys said about shimmy.
> They were wrong.  I can't take a bike that doesn't shimmy and change
> it into a bike that does shimmy.  Even though I don't have any ideas
> about the causes or the solutions, you should absolutely swap your
> headset to needle bearings if your bike shimmies and hope for the
> best, even though I don't know if it will help, and maybe will make it
> worse"
>

> Now don't get me wrong.  I don't understand shimmy, but I came to the
> article with the attitude of student.  The only other articles I've
> read on the topic are Sheldon Brown's (RIP) very brief glossary
> discussion and the Jobst Brandt article.  For Jan to put the single
> word "Shimmy" on the cover, and to title his article "What Causes
> Shimmy?" suggests that he knows something.  The article content itself
> suggests to me that Jan might not know any more about shimmy than any
> of us.  That's not necessarily a bad thing: I'm convinced it's a
> complex problem.  But I'd almost rather see a person in a pedagogical
> position of leadership to say "Hey, I know a lot, but I don't
> understand shimmy.  Here's some anecdotal observations I've made.
> Here's some anecdotes I've heard, but haven't verified." and just end
> it there.
>

[Ken Freeman]

Which must the Motown view ...

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Ken Freeman
Ann Arbor, MI USA

[Montclair BobbyB]

... at 57 mph in a turn I was afraid of that bike at speed ...

Only thing crazier I've ever heard of was Arlo Gutherie riding his
motorcycle down the mountain road... playin' his guitar... Geez,
Kelly, STFD... gonna kill yourself.

[Kelly]

So you're saying the harmonics of the guitar may stop the woble?  Good thought there. :)

 

[Ken Freeman]

Or those of the background singers?

On Sun, Dec 12, 2010 at 12:28 PM, Kelly <tksl...@gmail.com> wrote:

So you're saying the harmonics of the guitar may stop the woble?  Good thought there. :)

 

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[EricP]

As long as they don't have harps, you're safe. (Bad joke, totally
admit it.)

Good for you for getting the bike up to 57. Have been up to 40 on the
Sam Hillborne. Fast enough for me.

No shimmy on that descent. Unless my knocking knees caused something.

Eric Platt
St. Paul, MN

On Dec 12, 1:07 pm, Ken Freeman <kenfreeman...@gmail.com> wrote:
> Or those of the background singers?
>

> On Sun, Dec 12, 2010 at 12:28 PM, Kelly <tkslee...@gmail.com> wrote:
> > So you're saying the harmonics of the guitar may stop the woble?  Good
> > thought there. :)
>
> > --
> > You received this message because you are subscribed to the Google Groups
> > "RBW Owners Bunch" group.
> > To post to this group, send email to rbw-owne...@googlegroups.com.
> > To unsubscribe from this group, send email to

> > rbw-owners-bun...@googlegroups.com<rbw-owners-bunch%2Bunsubscrib­e...@googlegroups.com>
> > .

[Kelly]

Well being 220 lbs means gravity is my friend on the downhill. That
57 was scary with the wobble but have hit 65 mph on long straight shot
that was solid smooth and not scary at all. The desire to go that
fast has finally faded. I guess the adrenalin junky in me has settled
down.. another good reason to sell the race bike and get the ahh.. :)

But then the ride to starbucks and walgreens today was just as scary
as that speed :)
http://www.flickr.com/photos/tksleeper/sets/72157625582548862/

Kelly

> > Ann Arbor, MI USA- Hide quoted text -

[EricP]

Hey, I resemble that remark. 220 also. More a combination of not
having more major hills to descend and being a natural born chicken.
But, hey, we need the eggs.

Actually those photos aren't scary to me. In fact, would be nice to
have only that much snow on the ground. Could have been out riding
this weekend. We received 17 inches in the latest storm. Side roads
are still unplowed or at best two cars wide. With very compacted
snow. For me, that's scary.

Eric Platt
St. Paul, MN

[William]

I've run my first several experiments. My bike was in a state where
it was really easy to make it shimmy in a way that was/is not life
threatening. The bike is a 56cm Hillborne. It's got fenders, front
and rear racks a Saddlesack Large on the back and a Trunksack small in
front. Riding no hands on smooth flat road it shimmies about 3/4"
amplitude at the stem bolt at about 4Hz. Putting a knee on the top
tube stops it. I wanted to start with things that I can change for
free on the bike and see how that affects shimmy.

Test 1: Pump up front tire (Jack Brown blue) from 30psi to 70psi.
Result--no change. Still shimmies at will
Test 2: Pump up rear tire (JB blue) from 30psi to 70psi. Result--no
change. Still shimmies exactly the same
Test 3: Remove Trunksack and contents from front of bike (3-4lbs of
weight). Result--no change. Still shimmies easily, same amplitude,
same frequency as far as I can tell
Test 4: Remove Saddlesack Large and contents from the back (10-12lbs
of weight). Result--shimmy GONE. I can't get it to move at all

I'm going to start adding weight back on to the bike, beginning with
the front. I'll keep experimenting.

The fundamental conclusion I can make already is that front end shimmy
at moderate speed no-handed is not a fundamental property of this
bicycle. It's a property of a particular configuration on this
bicycle. If I don't like it, I can configure this bike differently.
If I choose to configure my bike this way, I should be prepared to
accept some shimmy. Jan's article encouraged me to experiment, and
I've started doing that, and I'm learning more about my bike, and
that's all good stuff.

[james black]

On Mon, Dec 13, 2010 at 16:13, William <tape...@gmail.com> wrote:
> The fundamental conclusion I can make already is that front end shimmy
> at moderate speed no-handed is not a fundamental property of this
> bicycle.

What kind of rear rack do you have? Based on your account, I'm
guessing that an overly flexible rear rack is contributing to the
shimmy problem on your bike. I really wouldn't expect a bike with the
geometry and stout tubing of the Sam Hillborne to shimmy under less
than extreme loading, and was surprised to read your account when you
first brought it up.

James Black
Los Angeles, CA

[Seth Vidal]

On Mon, Dec 13, 2010 at 7:13 PM, William <tape...@gmail.com> wrote:
> The fundamental conclusion I can make already is that front end shimmy
> at moderate speed no-handed is not a fundamental property of this
> bicycle.  It's a property of a particular configuration on this
> bicycle.  If I don't like it, I can configure this bike differently.
> If I choose to configure my bike this way, I should be prepared to
> accept some shimmy.  Jan's article encouraged me to experiment, and
> I've started doing that, and I'm learning more about my bike, and
> that's all good stuff.

How much do you weigh + yourstuff?
How Are the bars set up vis-a-vis the saddle?

-sv

[William]

It's a Nitto R-14. The saddlesack large does flop around when you
rock the bike, so the compliance that I think you are correctly
seeking might be there as well.

On Dec 13, 4:19 pm, james black <chocot...@gmail.com> wrote:

[William]

I weigh about 175. The whole bike rig with both bags on it as
described above is probably in the low 40s. So maybe 215 bike + cargo
+ rider. Straight medium. :)

My bars are 1-2 inches above saddle height.

On Dec 13, 4:21 pm, Seth Vidal <skvi...@gmail.com> wrote:

[Bill]

Builder Dave Moulton sheds some light on the subject in this 2006 blog
entry:

http://davesbikeblog.squarespace.com/blog/2006/8/18/shimmy-re-visited.html

[William]

Yeah, I've read that article. What "light" were you referring to?

In that article he definitely makes himself look smart by describing
'nutation' which is a term that 99.9% of his readers don't know. He
describes that as a driving force for why bikes shimmy, but has only
guesses for why bikes don't shimmy. He says the bikes he built don't
shimmy, and after the fact guesses why they don't. He also has
specified and implied things to try if your bike does shimmy, but just
like anyone else, he can't specify a combination of things that will
yield shimmy.

As a group, these experts all seem to regard shimmy the way any of us
would. It's an unpleasant attribute of a bike that you'd just like to
have go away, so you can resume enjoying yourself on your bike. Just
change stuff and expect that eventually you'll find a configuration
that behaves more like you want. If you find such a configuration, be
happy and ride. If it comes up again, repeat the process. The
experts with whom you consult might have their own pet remedy to try
first, and take it for what it's worth, an educated guess.

For my experiments, I've moved to loading my Bombadil with bullmoose
bars with the identical load that the shimmy-Hillborne had. Nitto
Mini and small trunksack in front. Nitto R-14 and Saddlesack Large in
back. I'll ride that around (weather permitting) and see what comes
of that.

On Dec 17, 3:34 pm, Bill <webe...@gmail.com> wrote:
> Builder Dave Moulton sheds some light on the subject in this 2006 blog
> entry:
>

> http://davesbikeblog.squarespace.com/blog/2006/8/18/shimmy-re-visited...

[William]

Update on the research front. In the next round of testing I put the
identical load on a different bike.

I loaded my 56cm Bombadil with the trunksack small on the Nitto Mini
front. I moved the Nitto R-14 rear and the loaded Saddlesack Large
over to the Bombadil. The Bombadil does shimmy with that load. But
it is at a much higher frequency and a smaller amplitude. The
amplitude was almost small enough to just ignore. It also happened at
a somewhat higher speed. More notes for the notebook.

[doug peterson]

William:

Did you note the weights at each end? Riv says the R-14 isn't meant
for much weight (don't recall the number but it's conservative) so
perhaps some rack movement?

dougP

> > > > > -sv- Hide quoted text -

[james black]

On Tue, Dec 21, 2010 at 13:25, William <tape...@gmail.com> wrote:
> I loaded my 56cm Bombadil with the trunksack small on the Nitto Mini
> front.  I moved the Nitto R-14 rear and the loaded Saddlesack Large
> over to the Bombadil.  The Bombadil does shimmy with that load.  But
> it is at a much higher frequency and a smaller amplitude.  The
> amplitude was almost small enough to just ignore.  It also happened at
> a somewhat higher speed.  More notes for the notebook.

The R-14 looks to my eye like it would be very flexible. I still think
that it is the main culprit here. It would be an interesting
experiment to keep everything the same but have the bag on a stiffer
rack.

[William]

I'm tracking that...In my notes I estimated the Sackville Saddlesack
Large and it's contents weighed 12 pounds. There are numerous
speculations in the literature about high mounted floppy loads being
associated with shimmy. Nobody conclusively says that such things are
causes or enablers of shimmy, or will bet their life on removing such
loads being a cure to shimmy.

Another near-term experiment will be to load the same Saddlesack large
to a much stiffer rear rack. The Hillborne now has the rack that came
with my Burley Piccolo. It's a beast. Fat cro-mo tubes welded,
bomber. If the shimmy comes from rear load floppiness, and if the
critical flopiness comes from the rack, then that Burley rack should
change the shimmy properties substantially. If the critical flopiness
comes from the Saddlesack large, then the rack won't change
anything.

[Steve Palincsar]

On Tue, 2010-12-21 at 14:29 -0800, William wrote:
> Nobody conclusively says that such things are
> causes or enablers of shimmy, or will bet their life on removing such
> loads being a cure to shimmy

They'd be very foolish to do so, since there are many things that can
cause shimmy including rider behavior.

> Another near-term experiment will be to load the same Saddlesack large
> to a much stiffer rear rack. The Hillborne now has the rack that came
> with my Burley Piccolo. It's a beast. Fat cro-mo tubes welded,
> bomber. If the shimmy comes from rear load floppiness, and if the
> critical flopiness comes from the rack, then that Burley rack should
> change the shimmy properties substantially. If the critical flopiness
> comes from the Saddlesack large, then the rack won't change
> anything.

I hope you solve your problem, but when you've done it you still won't
be able to make any kind of sweeping, definitive statement about what
causes and what cures shimmy. At most you'll be able to say "I did this
to cure mine."

[Michael_S]

I was thinking another variable may be wheels. Have you tried swapping
wheels from another bike to see if that changes or helps anything? Or
tire switching as well?
both seem like easy changes to make. Rotating components can certainly
affect the dynamic response of the bike.

Other things like frame alignment, new headsets and such are more
costly to do.

Keep trying..
~Mike~

[William]

I understand it well enough on my Hillborne that I can avoid shimmy
when I want to, so I don't think I have a problem to solve. We've
never read a convincing description for why bikes shimmy, that's
true. But I'd argue we've never read a convincing description for why
any INDIVIDUAL bike shimmies. At least I want to get to that
point.

The thing I'm doing that I think differs from the 'experts' is that
I'm deliberately making it happen to see if I can develop a more
general understanding. The thing I've not seen in any of the commonly
cited articles (Heine, Brandt, Moulton, Sheldon(RIP)) is that in none
of them has the author deliberately made shimmy happen in order to
study it. They all report their own experiences and second hand
rumors of poking around trying to fix it on somebody's bike (only
sometimes their own) and guessing at what the causes were and what
worked after the fact.

My hypothesis is that it's a tuned resonance problem. When multiple
structures have matching resonant properties they get to ringing at
max amplitude. If that's what you have, changing the resonant
frequency of one, so that it doesn't match the other will make the
ringing subside. The Taipei 101 skyscraper has a relatively tiny
pendulum near its roof to cancel out resonance of the building from
earthquakes. Several, maybe all the authors above would agree it's a
tuned resonance problem, but they don't agree on what the resonating
subsystems are. If you don't know what they are, you certainly can't
deliberately and precisely tune or de-tune them. Jan suspects that
the top tube and the down tube are separate resonators, and that bikes
that have the same diameter tubing in the top tube and the downtube
are tuned to each other and are much more likely to shimmy. Moulton
guesses that the chainstays are in some way a semi-isolated subsystem
and his use of Columbus SP tubing in chainstays gave his bikes anti-
shimmy properties. Others say that frame flex has nothing to do with
any of this.

On Dec 21, 2:37 pm, Steve Palincsar <palin...@his.com> wrote:

[doug peterson]

Just looked up the R-14 on Riv's site: 13 lbs capacity. It's
surprising how quickly weight can add up. The R-14 is an elegant
looking rack but with just the support struts for stability it may
lack lateral stiffness.

dougP

On Dec 21, 2:20 pm, james black <chocot...@gmail.com> wrote:

[andrew hill]

I've got a 56 Sam that I ran a R-14 on with 2 Ortliebs fairly well loaded, or (alternatively) a Big Loafer on top... nary a shimmy (with a mini+loaf on the front).

ymmv, of course, but i never noticed any "flexiness" from the R-14.

-a

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[neurodrum]

whups, scratch that - i've used the R-FIFTEEN, not the R-14.

-a

[Rene Sterental]

I was thinking that the factor is the weight of the rear bag, not the
rack. Can you verify if without the rack but with the bag anything
changes?

My Atlantis with the same rack-bag combo + Noodle bars and shimmies.
When I put the Albatross bars it didn't shimmy but I couldn't get used
to them. Now I'm putting the Noodles back on and will see what
happens. Running 50mm Marathon Supremes.

Rene

Sent from my iPhone 4

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[Tim McNamara]

Try the simple things first: move the saddle slightly forward or
back, maybe 1/2", to change the weight distribution of you on the
bike. Change the distribution of stuff you carry on the bike (or
consider carrying less stuff). Raise or lower the bars to change
your position. Make sure the headset is adjusted. Make sure the
wheels are true and properly aligned in the frame. Swap the front
tire to the back and vice versa; look for casing defects in the
tires. Try less inflation pressure (or more) in the tires. Try a
different size tire. If your bike starts to shimmy with your hands
on the bars, stand up slightly and ease your weight off the saddle-
this will usually stop a shimmy instantly.

The cause of shimmy is not exactly known. Since it tends to be speed-
dependent, it is likely that vertical and gyroscopic forces play a
part. There appear to be at least two fulcrum points, the rear tire
contact patch and the saddle. The bike frame appears to act as a
spring, whipping back and forth; nutation can be observed with the
steerer turning slightly in the head bearings as the front part of
the frame travels laterally. Interestingly the front tire contact
patch usually continues to track in a straight line but, as the
shimmy worsens, the contact patch can begin to arc back and forth on
the road. This is what is often meant when someone talks about a
death wobble, because the vehicle becomes unstable and will often
crash unless the wobble can be stopped. Wobbles can be started by
road surface irregularities

*Great* video by the much-missed-in-rec.bikes.tech Damon Rinard of a
deliberately induced no-handed shimmy:

http://www.youtube.com/watch?v=xODNzyUbIHo

I wish that was in slo-mo.

This is Rob English crashing at the Battle Mountain IHPVA event on
level terrain at about 70 mph (I bet he appreciated his fairing very
much). It appears to me that his pedaling effort caused the problem
and that as the bike started to wobble, his pedaling amplified it.

http://www.youtube.com/watch?v=i5Dapy1xUq0

My observations with my bikes (a 1996 Riv A/R [26 x 1.25], a 1995
Ritchey Road custom [700 x 25], a 1998 Gunnar Crosshairs [700 x 28]
and a home-built road bike [700 x 25] all with Panaracer Pasela tires
at the rated maximum pressure) is that:

1. none of them currently shimmy with my hands on the bars.

2. the Gunnar shimmied when I mounted a Nitto mini-rack on the front
fork, even with no load on the rack, and stopped as soon as I removed
the rack- I could feel the pulsation in my hands when they were on
the bars. The Gunnar sometimes shimmies if I ride no handed and lean
back. Reynolds 853 with Waterford fork upgrade. Oddly it did not
shimmy with a really old Eclipse bar bag (one of the ones from the
late 70s with a rack that slipped over the bars and under the stem
and with elastic cords going down to the dropouts).

3. the Riv doesn't, with or without the same Nitto mini rack, with
or without a load. Reynolds 753 frame with 531 fork. No shimmy that
I can ever recall having on this bike.

4. the Ritchey shimmies at certain speeds no-handed (19-20 mph and
up) if coasting but not if pedaling; worse if I lean back. Tange
Prestige Ritchey Logic tubes and fork tubes.

5. the home built bike shimmies occasionally no-handed. Reynolds
501 frame and fork tubes.

5. the scariest shimmy I ever had was descending on a Bianchi
Reparto Corsa-built bike when I tried the aero trick of sliding off
the back of the saddle. It felt like the rear wheel was shimmying,
very disconcerting. The Ritchey replaced that bike and handles so
much better than the Italian job.

[Philip Williamson]

Tim wrote:
> This is Rob English crashing at the Battle Mountain IHPVA event on  
> level terrain at about 70 mph (I bet he appreciated his fairing very  
> much).  It appears to me that his pedaling effort caused the problem  
> and that as the bike started to wobble, his pedaling amplified it.

Totally non-Riv content, but it's a small world of awesome - that's
the same Rob English who built my favorite 18.5 lb steel 29er at the
Oregon Handbuilt Bicycle Show: http://www.biketinker.com/2010/fine-bikes/english-cycles-mountain-bike/
And this 11.5 pound steel road bike: http://www.flickr.com/photos/philipwilliamson/5067220826/

Coincidentally, a related Youtube video shows Rob explaining how to
stop shimmy on a Bike Friday... all the same things just mentioned,
but no magic hammer.

Philip

Philip Williamson
www.biketinker.com

[William]

The drinard video is very good. That's exactly the thing I'm looking
at when running my experiments.

[doug peterson]

I've run similar loading experiments on my Atlantis. The unloaded set-
up is a Nitto small front rack with Acorn Box Rando bag which I often
load up to 6-8 lbs without issue. I have a Nitto Big Rear Rack (2 lbs
of real steel) for anything I may pick up along the way. Unless I've
got a box of books or similar casually strapped to the back, the bike
is stable although the steering feels a bit wandering if I need to
take both hands off the bars. Not a big deal.

The Atlantis will shimmy with extra weight only on the rear (2
panniers, total weight less than 20 lbs), such as a lodging tour
load. Move that same load to front low riders, no shimmy. Add
another pair of panniers for camping (15 lbs total), and the most
stable arrangement is with the lighter pair on the rear. 4 bags, with
the heavier on the rear, and the bike has that "tail wagging the dog"
feel, and has developed a nasty shimmy more than once.

The above is all with the same 35 mm touring tires and a 175 lb
rider. I've fiddled with the headset adjustment, etc., and will
change to a needle bearing HS when the present one dies. My
conclusion, for me & what I do with the bike, is to put the bulk of
any load on the front, with whatever's left over on the rear.

William may have reached the same conlusion in his post where he
reports eliminating the shimmy when he removed the rear saddlebag (12
lbs). In any case, these experiments are great fun to perform and we
learn a lot about our bikes, preferences, and what works for us. Rene
(above) is the only other Atlantis owner I can recall posting about
shimmy.

dougP

> > much better than the Italian job.- Hide quoted text -

[William]

Doug

I am arriving at that conclusion and towards that end I'm also
prepared to rule out one compelling variable. My experiments suggest
that the compliance (flexibility) of the rear rack itself is NOT a
significant contributor to shimmy on my Hillborne.

The experiment was that I swapped rear racks between the Hillborne and
the Bombadil. The Nitto R-14 was the original Hillborne rack and we
speculated whether that minimalist rack could be flexing at a resonant
frequency that matched the front end of the bike and resulted in
shimmy. My Burley brand cromoly rack is WAY stiffer, and with a
similar load, the Hillborne shimmies exactly like it did with the
R-14.

In a related experiment, the Bombadil shimmies with a similar load on
it, also with both racks. The shimmy on the Bombadil differs in
frequency(higher) and amplitude(smaller), but it does it.

That's excellent progress, I think. Next step I'll try to fix a
shimmy state by adding weight in the front and leaving the weight in
the back constant.

On Dec 22 2010, 6:54 pm, doug peterson <dougpn...@cox.net> wrote:
> I've run similar loading experiments on my Atlantis.  The unloaded set-
> up is a Nitto small front rack with Acorn Box Rando bag which I often
> load up to 6-8 lbs without issue.  I have a Nitto Big Rear Rack (2 lbs
> of real steel) for anything I may pick up along the way.  Unless I've
> got a box of books or similar casually strapped to the back, the bike
> is stable although the steering feels a bit wandering if I need to
> take both hands off the bars.  Not a big deal.
>

> The Atlantis willshimmywith extra weight only on the rear (2

> panniers, total weight less than 20 lbs), such as a lodging tour

> load.  Move that same load to front low riders, noshimmy.  Add

> another pair of panniers for camping (15 lbs total), and the most
> stable arrangement is with the lighter pair on the rear.  4 bags, with
> the heavier on the rear, and the bike has that "tail wagging the dog"

> feel, and has developed a nastyshimmymore than once.

>
> The above is all with the same 35 mm touring tires and a 175 lb
> rider.  I've fiddled with the headset adjustment, etc., and will
> change to a needle bearing HS when the present one dies.  My
> conclusion, for me & what I do with the bike, is to put the bulk of
> any load on the front, with whatever's left over on the rear.
>
> William may have reached the same conlusion in his post where he

> reports eliminating theshimmywhen he removed the rear saddlebag (12

> lbs).  In any case, these experiments are great fun to perform and we
> learn a lot about our bikes, preferences, and what works for us.  Rene
> (above) is the only other Atlantis owner I can recall posting aboutshimmy.
>
> dougP
>
> On Dec 22, 11:09 am, William <tapebu...@gmail.com> wrote:
>
> > The drinard video is very good.  That's exactly the thing I'm looking
> > at when running my experiments.
>
> > On Dec 21, 9:34 pm, Tim McNamara <tim...@bitstream.net> wrote:
>
> > > Try the simple things first:  move the saddle slightly forward or  
> > > back, maybe 1/2", to change the weight distribution of you on the  
> > > bike.  Change the distribution of stuff you carry on the bike (or  
> > > consider carrying less stuff).  Raise or lower the bars to change  
> > > your position.  Make sure the headset is adjusted.  Make sure the  
> > > wheels are true and properly aligned in the frame.  Swap the front  
> > > tire to the back and vice versa; look for casing defects in the  
> > > tires.  Try less inflation pressure (or more) in the tires.  Try a  

> > > different size tire.  If your bike starts toshimmywith your hands  

> > > on the bars, stand up slightly and ease your weight off the saddle-  
> > > this will usually stop ashimmyinstantly.
>

> > > The cause ofshimmyis not exactly known.  Since it tends to be speed-

> > > dependent, it is likely that vertical and gyroscopic forces play a  
> > > part.  There appear to be at least two fulcrum points, the rear tire  
> > > contact patch and the saddle.  The bike frame appears to act as a  
> > > spring, whipping back and forth; nutation can be observed with the  
> > > steerer turning slightly in the head bearings as the front part of  
> > > the frame travels laterally.  Interestingly the front tire contact  
> > > patch usually continues to track in a straight line but, as the  

> > >shimmyworsens, the contact patch can begin to arc back and forth on  

> > > the road.  This is what is often meant when someone talks about a  
> > > death wobble, because the vehicle becomes unstable and will often  
> > > crash unless the wobble can be stopped.  Wobbles can be started by  
> > > road surface irregularities
>
> > > *Great* video by the much-missed-in-rec.bikes.tech Damon Rinard of a  
> > > deliberately induced no-handedshimmy:
>
> > >http://www.youtube.com/watch?v=xODNzyUbIHo
>
> > > I wish that was in slo-mo.
>
> > > This is Rob English crashing at the Battle Mountain IHPVA event on  
> > > level terrain at about 70 mph (I bet he appreciated his fairing very  
> > > much).  It appears to me that his pedaling effort caused the problem  
> > > and that as the bike started to wobble, his pedaling amplified it.
>
> > >http://www.youtube.com/watch?v=i5Dapy1xUq0
>
> > > My observations with my bikes (a 1996 Riv A/R [26 x 1.25], a 1995  
> > > Ritchey Road custom [700 x 25], a 1998 Gunnar Crosshairs [700 x 28]  
> > > and a home-built road bike [700 x 25] all with Panaracer Pasela tires  
> > > at the rated maximum pressure) is that:
>

> > > 1.  none of them currentlyshimmywith my hands on the bars.

>
> > > 2. the Gunnar shimmied when I mounted a Nitto mini-rack on the front  
> > > fork, even with no load on the rack, and stopped as soon as I removed  
> > > the rack- I could feel the pulsation in my hands when they were on  
> > > the bars.  The Gunnar sometimes shimmies if I ride no handed and lean  
> > > back. Reynolds 853 with Waterford fork upgrade.  Oddly it did not  

> > >shimmywith a really old Eclipse bar bag (one of the ones from the  

> > > late 70s with a rack that slipped over the bars and under the stem  
> > > and with elastic cords going down to the dropouts).
>
> > > 3.  the Riv doesn't, with or without the same Nitto mini rack, with  
> > > or without a load.  Reynolds 753 frame with 531 fork.  Noshimmythat  
> > > I can ever recall having on this bike.
>
> > > 4.  the Ritchey shimmies at certain speeds no-handed (19-20 mph and  
> > > up) if coasting but not if pedaling; worse if I lean back.  Tange  
> > > Prestige Ritchey Logic tubes and fork tubes.
>
> > > 5.  the home built bike shimmies occasionally no-handed.  Reynolds  
> > > 501 frame and fork tubes.
>

> > > 5.  the scariestshimmyI ever had was descending on a Bianchi