unstable front end?

[Geoff]

What causes the front end of a bike to become unstable at speed? I was riding yesterday and once I hit a good down hill at about 40mph the front started to get really squirlly, I almost lost it. I have had some shimmy before but nothing this bad. Also I have never noticed it on a sprint lead out only down hill. The bike is a Lemond Victorie with the issue fork and it fits well.

Any answers, comments, or wise cracks wanted.

Geoff

[e-RICHIE]

What causes the front end of a bike to become unstable at speed? I was riding yesterday and once I hit a good down hill at about 40mph the front started to get really squirlly, I almost lost it. I have had some shimmy before but nothing this bad. Also I have never noticed it on a sprint lead out only down hill. The bike is a Lemond Victorie with the issue fork and it fits well.

Any answers, comments, or wise cracks wanted.

Geoff


often it's caused by a momentary lapse in concentration.

[Geoff]

Its possible that my little mind has trouble staying focused, but the shimmy is always there on this bike and I have not noticed it on my Atlanta.

It could be that my lack of concentration causes me to exagerate the movement.

What would could be a cause of the shimmy to begin with? Fork, Fit, Geos?

Maybe its just me.

Geoff

[dirtdigger88]

try and get a copy of the latest Rivendell Reader- if need be pm me a fax number and Ill send you the pages-

there is a good article explaining the shimmy-

number #37 I think-

Jason

[e-RICHIE]

What would could be a cause of the shimmy to begin with?
my highly opinionated post from a 2002 CR list thread atmo. (http://search.bikelist.org/getmsg.asp?Filename=classicrendezvous.10207.0504.e ml)

and a follow-up post yo - (http://search.bikelist.org/getmsg.asp?Filename=classicrendezvous.10207.0507.e ml)

[Geoff]

e-RICHIE,

Well I never knew that I was chickin!

However, I had left my helmet at work on Friday and had been riding with out it, which I rarely do these days and maybe I was being more concerned that other wise. Normally I love the down hills I was just at the Tour of Georgia and hit 55 mph and loved it.

I will agree with what I think is a premiss to your satement, that you really need to attack downhills, leadouts, etc. for them to be successfull and for you to be focused at that kind of effort.

Does the knee on the top tube work?

Dirt,

I will see if I can find it.


Know if you will I will curl up in the corner and cower while I wait for my computer to refresh and see if there are anymore posts of this.

[Bradford]

I’ve had a couple of shimmy problems in the last few years and I’m pretty sure it was pilot error. I sure don’t know what causes shimmy in general, but I think I know what caused it with me.

For me, it seems to have been how I was sitting on the bike. I never had a bike shimmy until I started riding a tandem. Since my wife doesn’t like to ride aggressively, spending a lot of time on the tandem made my decent less aggressive as I started to sit up and back more. In addition, it really bothers her to have one pedal down and one pedal up, so I started descending with both feet even. After having a bad shimmy incident at Open House last year, Ron Kiefel suggested that the problem was that I needed to put the outside foot down to put some tension into the bike. I tried it, and it also put me back into a more aggressive posture like I used to use before I started with the tandem.

I may not have enough experience to know if this makes sense or not, but Ron does, and it works, so I’m back to a more aggressive posture with the outside foot down and a little pressure on the pedal. So far, I’m back to shimmy free.

[Ray]

Geoff,

There are a few different possible sources of shimmy. In my cases, it's almost always been because of high winds on a fast and hairy descent and my nerves in that situation causing too tight a grip on the bars and too much tightness in my upper body (its happened twice in the last year, same basic situation each time). Once I remember to relax, I'm almost always fine. But when it happens, yeah, I've always found the knee against the top tube works, although sometimes I've had to clamp the tube with both knees.

Good luck,

-Ray

[e-RICHIE]

So far, I’m back to shimmy free.
sweeeet

[Birddog]

I've had it occur on several occasions, different bikes too. I was able to determine that a particular bike had a tendency to shimmy at a particular speed. The shimmy usually (but not always) started after hitting a small irregularity in the road surface and sometimes would turn violent. What works for me is to loosen my grip on the bars. I found that I had a "death grip" on the bars, and that was a major contributor to the problem. Since becoming aware of the "grip" issue, I've had nary a problem, but the knee trick works. Sometimes it takes a leap of faith to lighten your grip as the shimmy increases. Try and set up the shimmy on purpose and see if this helps.

Birddog

[Eric E]

So, if I can quote e-richie:

"for the rest of us, when it comes to the issue of shimmy, and descending speeds, and the related issues, i say it's all pilot error."

I suspect that there are cyclists that can conquer all vibrational instabilities. Not me - I do possess some imagination as to what can happen at high speed, and thus will brake and thus tighten up going down many of our Colorado mountains.

On an earlier version of my Ti Rapid Tour (custom geometry w/ 72 degree seat tube), braking and other "pilot errors" caused my bike to shimmy. Serotta, to their credit, worked with me on this, getting me to increase the spoke tension on my custom wheels (their low tension made the shimmy life threatening to me), get a stiffer fork, and finally, when my bike was happily shimmying away while being passed by Huffies on a MS150, replaced the frame with one with a stiffer tube set (paticularly the rear triangle and top tube, I think).

Since that time, with the same semi-incompetent pilot, my bike has not shimmied - even with the sort of hard. panic braking like when a parked car pulls out in front of you on a downhill - this would bring it on the earlier frame.

Enjoy, Eric

[TimD]

With all due respect to e-Ritchie, I don't believe shimmy is exclusively due to pilot error, from personal experience.

I once owned a Trek 5000 which was exceedingly nervous over 35 MPH.
Behavior was independent of wheelset, position on the bike (with a caveat, see below), force on the bars, crosswinds, etc. Same road, same hill, same rider, three other bikes - no problem.

There's a theory that the front end can only oscillate if anchored by a large
mass, and lifting your butt off the saddle temporarily will stop the oscillation.
Since my current bikes don't exhibit "death wobble", I haven't tested this
theory.

My $0.02
TimD

[bironi]

Geoff,

Make sure your head has not come loose. This will cause shimmy.

[e-RICHIE]

Geoff,

Make sure your head has not come loose. This will cause shimmy.


i can agree with this atmo -

[11.4]

In addition to a loose head, also check your headset. That can cause the same problem.

Seriously, I've found some frame or component issues that can contribute to shimmy. On frames, I've seen poorly built frames with excessively flexible top tubes that don't hold the head tube and steer stable on certain kinds of roads. It takes quite a screwed up frame to do this, however. On components, I've seen loose headsets and significant mis-dishing of wheels cause problems. These are all problems that tend to start up gradually and can be managed, albeit with inconvenience. There's also of course the selection of too high a profile rim for the wind conditions and a rider's handling skills -- especially on the front, having to stabilize a wheel that the wind wants to turn can create instabilities as well. The usual response is to tighten up on the bars.

Positioning is actually one of the biggest issues. On the track, if you have too much weight distribution towards the front, you'll have trouble keeping stability on the banking -- you'll feel very twitchy and tend to swing off the pole. Too much weight on the front not only encumbers steering a bit, but also takes weight off the rear -- the result is that your front wheel is doing too much work and your rear wheel isn't stabilizing your line of travel. If you start wobbling, in some ways it's actually coming from the rear wheel, not the front, because the rear isn't doing what it needs to help out the front wheel. This same kind of issue shows up on the road, of course, and when you're pointed downhill, you're naturally weighting the front more.

How to handle this? First, just learn how to expect it and handle it. Second, shift your weight on a downhill to minimize the effect. Third, don't pick a position for the most absolute aero position on the flats if you're going to have to ride that position on downhills as well. Your position is always a compromise and you have to take downhill stability into consideration. You might note that this shimmy problem has become more publicized since threadless headsets came into existence, leading me to suspect that people are setting their bars lower and not able to make the simple quill stem height adjustment that cures the issue. You'll notice that the great descenders do not have a huge drop from the saddle to their bars, and they're able to ride more in their drops because of this as well. Everyone wants a position like Tom Boonen's, but we don't all have the arms and torso to suit. Plus, Tom isn't the greatest descender with his position either. There's a lesson to learn in every bike you look at.

[Orin]

So, if I can quote e-richie:

"for the rest of us, when it comes to the issue of shimmy, and descending speeds, and the related issues, i say it's all pilot error."

I suspect that there are cyclists that can conquer all vibrational instabilities. Not me - I do possess some imagination as to what can happen at high speed, and thus will brake and thus tighten up going down many of our Colorado mountains.

On an earlier version of my Ti Rapid Tour (custom geometry w/ 72 degree seat tube), braking and other "pilot errors" caused my bike to shimmy. Serotta, to their credit, worked with me on this, getting me to increase the spoke tension on my custom wheels (their low tension made the shimmy life threatening to me), get a stiffer fork, and finally, when my bike was happily shimmying away while being passed by Huffies on a MS150, replaced the frame with one with a stiffer tube set (paticularly the rear triangle and top tube, I think).

Since that time, with the same semi-incompetent pilot, my bike has not shimmied - even with the sort of hard. panic braking like when a parked car pulls out in front of you on a downhill - this would bring it on the earlier frame.

Enjoy, Eric


Yeah, me too... just over 20 mph, no hands. Knee against the top tube stopped it. Hasn't happened with any other bike I've owned. Of course, I could keep my hands on the bars and avoid that particular manifestation, but there were the times when it felt like it was trying to shimmy in a corner, a really squirelly feeling, causing me to exit the corner wider than planned.

I ran an F1 fork on it while Serotta re-raked the fork and didn't notice any problem during that time. Now with the fork raked to 43mm (73 deg head angle), I've only had one bad corner which _could_ have been explained by the road being slightly bumpy... but the same corner and line hasn't produced the same squirelly feeling on other bikes.

Orin.

[Samster]

often it's caused by a momentary lapse in concentration. like what happens when you're out of gas...

[e-RICHIE]

like what happens when you're out of gas...


i think some are afraid to admit this atmo -

[telenick]

Craig Calfee has a very good article (http://www.calfeedesign.com/pdf/Fork_Symmetry.pdf) on this.

Bottom line: there are many factors that can induce a speed wobble. They range from a shivering rider to wind wash in the spokes to frame vibration to frame geometry and on and on. Logical deduction will help you rule out many variables.

[jerk]

the jerk has never had a bike shimmy.

jerk

[Fixed]

bro I haven't either unless it had a flat tire .
cheers

[chrisroph]

My guerciotti track bike shimmied one time when I was doing a miss and out riding at the back and I was real stupid and accelerated to the inside. Of course, as the group crossed the line, it slowed. Because I was accelerating at the rear of the group and going to the inside, the only place I could go was to the apron. So, I found myself rapidly approaching the bank on the apron with the tail of the group on my right. My natural reaction was to clench my arms to brace for the inevitable carnage I was sure would result from me hitting the 45deg Alpenrose bank at 28 mph with the group flying by. Fortunately, my old motocross instincts kicked in and I used the bank like a berm to assist my left turn. That was the only time I pulled that bonehead move.

That experience bolsters the statements that shimmy is the result of rider reactions.

Interestingly, when I bought my used legend, I was told it was a returned frame because the original buyer said it shimmied. I was given a money back guarantee. The frame is rock solid and seems to be perfectly aligned and built. I don't think I could get it to shimmy if I tried.

[shinomaster]

I made my super stable Atlanta shimmy bad once. I was flying fast down a long straigt hill from Estacada and swerved fast to avoid a rock in the road at 45+ mph.....I was turbo scared but I managed to get out of the situation unscathed.

[gone]

my highly opinionated post from a 2002 CR list thread atmo. (http://search.bikelist.org/getmsg.asp?Filename=classicrendezvous.10207.0504.e ml)

and a follow-up post yo - (http://search.bikelist.org/getmsg.asp?Filename=classicrendezvous.10207.0507.e ml)
I agree with this completely. I've had my Serotta over 50 MPH with no shimmy under lots of conditions. But then I had an accident in December and when I started riding again I rode like an absolute coward (amazing what a few broken bones'll do to you): cornering like a wuss and descending like a snivelling coward. Result: the same bike shimmied like mad, heck, I even got it to shimmy once at 18 MPH.

As I healed and began riding normally again, relaxation regained, speeds increased, life is good. One thing to keep in mind wrt relaxing your grip on the bars: you've got these two big gyroscopes (wheels) spinning like crazy that really want to go straight, you just need to relax and let it happen.

[Ken Robb]

I had a bike that I could not keep from shimmying at speeds over 32mph.
I had one that would always wobble at 35mph but clamping the top tube with my knees would always cure it.
I had one that sometimes would wobble and sometimes not. Knee on the tt or locking my elbows to my side would cure it.
None of the 9 bikes in my stable now wobble--period.

Some of my wobblers didn't wobble for other riders and some did. I tried different wheels on the worst wobbler of the bunch and it no longer wobbled at 32mph but at 35 mph it did.

There seem to be many factors that affect whether or not a bike will wobble including rider size, weight, position, and technique. I think my worst wobblers had forks too flexy for me at 200-215lbs.

The one that might/might not wobble was a fairly flexible ti frame.

[CalfeeFly]

To say that almost absolutely the problem is the rider is an insult to the many good riders that are on this forum. As was stated by Telenick there are a variety of other possible explanations.

In my case I had a shimmy on my Kestrel ONLY when it had one particular wheel on the front (a Rev X in true) and it ONLY started at 45 mph. The shimmy was so bad if I had been afraid it would have been face plant time. I had it happen twice on the same hill and then I came back with a different wheel the following week and all was fine and it has been on that hill forever and again on that and other bikes. Top speed so far on that hill has been 53.

I did learn one thing from this thread...I'd never buy a Sachs bicycle...anyone that egotisical I rather not have anything to do with. It amazes me that someone with his expertise would dismiss virtually all problems of this type to the pilot. The ego of the man is unreal. I wonder what his story will be when the right set of circumstances turns his bike into a bronco? Maybe he never goes that fast... :banana:

[dbrk]

There is a long and interesting piece about the role of rake and trail and front loads on the handling of bikes in new issue of Vintage Bicycle Quarterly. I am not sure I agree with all of Jan Heine conclusions (in fact, I am sure I do not...) but it is a serious look at what _might_ cause shimmy.

There is a post here regarding e-Richie's comments that confuses a gifted builder's hardwon experience and expertise for egoism. That writer should be so lucky as to own a Sachs.

dbrk

[e-RICHIE]

(lotsa stuff goes here)


why are you going this route?
from your personal anecdote, i believe you are saying the exact thing -

"In my case I had a shimmy on my Kestrel ONLY when it had one particular wheel on the front (a Rev X in true) and it ONLY started at 45 mph. The shimmy was so bad if I had been afraid it would have been face plant time. I had it happen twice on the same hill and then I came back with a different wheel the following week and all was fine and it has been on that hill forever and again on that and other bikes."

that i said in my off-site text (one which i introduced as being "highly opinionated") from 2002:
"if your bicycle shakes, it usually only shakes on one hill at one time. that is, it's not a day-to-day problem. personally, i see it as a momentary incident, one in which the rider's fore-aft shift came at an inopportune time. a poorly designed frame, or a rider on a frame that doesn't allow for proper balance, or a combination of both, 'could' be the culprit. i've seen all combos of head angles, rakes, front wheelbases, stem lengths...and there is no constant to the issue of shimmy."

i'm also kinda' surprised you didn't snip my 2002 text in which i say write:
"i think that notion of 'straighter' frames shimming more frequently than crooked frames is bull****."
did you even see/read that? i was referencing the fact that the original velonews article mentioned that misaligned frames had less of a chance to speed wobble than properly aligned frames (do). wouldn't you also find that odd, especially in light of the calfee article (posted by Telenick) in which speed wobble is ascribed to fork misalignment?

[Tom]

Never happened to me yet, don't know why it happens, but I was behind a guy one day in a charity ride when it did happen. It was impressive.

I also think that case might have been the rider causing it more than anything because the whole ride, a longer one, he was the one guy in the group that kept doing something where you went "huh?" a lot.

[Geoff]

Well Ive finally succeded in posting a good thread.

I checked my headset last night it was fine and my wheels are straight and tight by Joe Young

Sooo,

Next is to get out to this decent this weekend and test my nerve. I have always been a good decender and bike handeler, but I not to big of a man to admit I could have "lost my concentration". The death woble happened at the end of a very hard 50 mile effort so I could very well of been "out of gas".

Anyway I will try again this weekend at the begining and end of the ride and will post my results (unless it makes me look weak).

Geoff

[sspielman]

To say that almost absolutely the problem is the rider is an insult to the many good riders that are on this forum. As was stated by Telenick there are a variety of other possible explanations.

In my case I had a shimmy on my Kestrel ONLY when it had one particular wheel on the front (a Rev X in true) and it ONLY started at 45 mph. The shimmy was so bad if I had been afraid it would have been face plant time. I had it happen twice on the same hill and then I came back with a different wheel the following week and all was fine and it has been on that hill forever and again on that and other bikes. Top speed so far on that hill has been 53.

I did learn one thing from this thread...I'd never buy a Sachs bicycle...anyone that egotisical I rather not have anything to do with. It amazes me that someone with his expertise would dismiss virtually all problems of this type to the pilot. The ego of the man is unreal. I wonder what his story will be when the right set of circumstances turns his bike into a bronco? Maybe he never goes that fast... :banana:



I think that it is a mistake to judge any of Mr. Sachs comments as egotistical. I can't imagine anybody better qualified to make comments on anything related to the biomechanics of cycling. He is our generation's Ugo DeRosa ATMO, BRO

[David Kirk]

There's lots of wisdom out there on this subject and I'm not sure I have anything really new to add but...........

Every bike on the planet wobbles. There I said it and I feel better. Every bike ever made will wobble. Here's the catch - most only wobble at speeds we never see. If your bike only wobbles at 75mph who cares? If it wobbles at 28mph I know who cares.

When you have a bike that wobbles at an inconvienient speed you can't actually get rid of the wobble but you can change the speed at which it occurs. A different front wheel might change the "wobble speed", a different fork rake might too.......there are lots of ways to influence it.

Back in my day at Serotta "wobblers" were treated very seriously ( as I'm sure they are today). One of my lucky jobs was to get my arse hauled up to the top of a good sized hill (Lake D. or Spier Falls) and then I'd go like hell down the hill and observe the wobble. We would then make small controlled changes to the bike and see how that affected the wobble speed. I made a lot of trips down those hills. Generally speaking going with stiffer and or lighter stuff ( fork, front wheel, brifters, bars...etc) raised the wobble speed. Heavier of softer stuff ( fatter tires, looser spokes, longer stem, heavier shifters, heavier bars) will lower the speed. Sometimes to an acceptable speed (above normal riding speeds) and sometimes not.

Sometimes I would test a wobbler and it wouldn't wobble for me. It wobbled for the owner but not for me. That was a hard thing to deal with because I couldn't fix what wasn't there for me. The impact of the rider on the system is huge. A different weight or center of gravity will totally change the deal. Sometimes for the better and sometimes not. And a tense of loose rider would change the deal in a big way. During a test I would tense my body, move it fore and aft, sit up tall and tuck down low. It would make the wobble come and go like a switch.

Yes some bikes will wobble if the rider is nervous and has a death grip on the bars. A tight body doesn't damp vibration well while a loose one does. Years ago I owned a bike that would wobble hard enough at 18mph to throw me to the ground. It was hands off stable at 50mph but 18 was not good. If I held on loosely at 18 it would stop.

So there are plenty of things one can do to lessen the chance of wobble or to move it to a more acceptable speed range but there is nothing one can do to eliminate it completely.

Dave

[Orin]

At least my case wasn't due to a death grip on the handlebars... no grip at all! A light grip on the bars would damp it, but what really worried me was that the bike was trying to shimmy at the speeds I normally ride at.

Perhaps I should send it back to Serotta and let them try it as it's not built up at the moment. It is the best rando bike I've had, but I still don't trust it.

Orin.

[e-RICHIE]

...but what really worried me was that the bike was trying to shimmy at the speeds I normally ride at.


are we talking wheel flop from low trail measurements
or actual shimmy vis-a-vis* high(er) speed oscillations?



*french. very classy aclu.

[catulle]

Past a certain speed, I shimmy, not the bike, atmo. :no:

[Dr. Doofus]

I did learn one thing from this thread...I'd never buy a Sachs bicycle...anyone that egotisical I rather not have anything to do with. It amazes me that someone with his expertise would dismiss virtually all problems of this type to the pilot. The ego of the man is unreal. I wonder what his story will be when the right set of circumstances turns his bike into a bronco? Maybe he never goes that fast... :banana:


has richard sachs ever made a mistake involving a bicycle? sure. did he ever build one that wasn't spot-on perfect? yep. are those steps in learning past him? you bet. is he in a position to say "you don't decide the geometry. I decide the geometry"? absolutely. that's why you pay the three grand -- heck, that's what you're paying the three grand for -- otherwise you'd have doof's pal here in rock hill make you a copy of a stock colnago in his backyard shop (he makes those now and then, and they're good...he takes a design that works and he's a skilled craftsman...but he's the first to admit that he's not going to take body measurements and make you a custom frame...man knows his limits, bro). you're paying for the confidence that says "I know how to make this...now let me do it." in the meantime, he's a kooky sort with neat facial hair who airs his views on this forum...which makes him seem arrogant. he's probably just saying what a few dozen other builders think...namely, that bikes don't wobble, dudes wobble....


whatever

[Orin]

are we talking wheel flop from low trail measurements
or actual shimmy vis-a-vis* high(er) speed oscillations?



*french. very classy aclu.

Well, it was an oscillation of the handlebars, pretty much as I've always seen shimmy or a "tank slapper" in motorcycle terms described. How would wheel flop differ? A lower frequency of oscillation?

Yes, the trail was a little lower than I'd expect and the increase in trail after re-raking the fork has improved things.

The difference with my old Koga-Miyata Full Pro was marked. I could ride it no problems at the same speeds, hands on the bars or not. Imperfections in the road would momentarily deflect the front wheel, but it would recover with no oscillations. The Rapid Tour would start oscillating and with the oscillations getting bigger quickly. Either with the re-raked fork or the F1 (I don't remember which), it would still oscillate a little, but would damp out rather than get worse. I swapped wheels, took the rack off, did all the usual checks to no avail. I swapped wheels with the Koga-Miyata etc. with no change.

Orin.

[OldDog]

I was riding with my buddy Buc, flying down a long hill we ride often. Down, not up as its a bear, and we are not. I was on the left side of the lane, Buc the right as we rounded a corner to find a large branch down accross the road. I lock up my brakes, skidding in to the bushy end of the branch. Buc bunny hops the limb, maybe 5 - 6 inches in diameter, he must of jumped his bike a foot. When he landed he taco'd his front wheel (campy, dt and op). must have come down at just the right angle to the road to make it give way. He took maybe another 30 yards to stop riding out a nasty wobble. Unweighted, you could hardly turn the wheel as it scrapped the fork blades. Hope I never need to test my skills like that.

[catulle]

To say that almost absolutely the problem is the rider is an insult to the many good riders that are on this forum. As was stated by Telenick there are a variety of other possible explanations.

In my case I had a shimmy on my Kestrel ONLY when it had one particular wheel on the front (a Rev X in true) and it ONLY started at 45 mph. The shimmy was so bad if I had been afraid it would have been face plant time. I had it happen twice on the same hill and then I came back with a different wheel the following week and all was fine and it has been on that hill forever and again on that and other bikes. Top speed so far on that hill has been 53.

I did learn one thing from this thread...I'd never buy a Sachs bicycle...anyone that egotisical I rather not have anything to do with. It amazes me that someone with his expertise would dismiss virtually all problems of this type to the pilot. The ego of the man is unreal. I wonder what his story will be when the right set of circumstances turns his bike into a bronco? Maybe he never goes that fast... :banana:

Er, two things come to mind. First, it is cool to know that you won't be making the waiting list any longer. Pheww, it is pretty long as it is. Second, if I were back in English 101 I'd have a pretty good oxymoron to bring to class: "egotistical Richie". Don't shoot the messenger, atmo, e-RICHIE is as decent and humble as they make them. Really real, said the Archbishop of Boston, iirc. Hey, peace, it's only a wobble.

[Retinadoc]

Maybe my understanding of this phenomenon is simplistic, but I view speed wobble as a perfect storm event. If the right combination of speed, rider, wind, pavement, and equipment occurs the bike/rider hits its resonant frequency and starts to oscillate. Clamping the top tube with your knees changes this frequency and thus stops the oscillation.

This echoes David Kirk's statement that all bikes will wobble given the right speed and conditions.

Which brings me to a question. Should'nt the frame material have a direct impact on the incidence of speed wobble independent of the rider? Carbon, steel, and titanium all have different resonant frequencies . I would also think that changing a major component such as a fork or wheels could potentially "cure" a bike.

[David Kirk]

Maybe my understanding of this phenomenon is simplistic, but I view speed wobble as a perfect storm event. If the right combination of speed, rider, wind, pavement, and equipment occurs the bike/rider hits its resonant frequency and starts to oscillate. Clamping the top tube with your knees changes this frequency and thus stops the oscillation.

This echoes David Kirk's statement that all bikes will wobble given the right speed and conditions.

Which brings me to a question. Should'nt the frame material have a direct impact on the incidence of speed wobble independent of the rider? Carbon, steel, and titanium all have different resonant frequencies . I would also think that changing a major component such as a fork or wheels could potentially "cure" a bike.

Bingo!

Dave

[CalfeeFly]

A few clarifications...

e-Richie my reference wasn't to you but Sachs. I knew you were the messenger. I apologize for the confusion since you and another thought it I must not have been very clear at all.

Jerk...I'm sure Sachs makes a fine bike and I would be the last to tell a custom builder not to build to his specs but mine. However I know it happens. People get Craig Calfee to build the bike to match an older Colnago, Eddy or whatever. I can't understand that but they do it.

I'm sure Sachs could care less if I want to buy his bike or not. I still think to make a flat statement that the only wobble on a bike is due to the pilot is ludicrous. I know it happened to me and it wasn't my error. It only happened with the one front wheel and I have ridden the hill before and since with no trouble at all. In fact I look forward to it as an opportunity to hit 50 for a change as there are not any cross streets to worry about.

I agree that the pilot could cause a shimmy but that isn't the only reason.

[e-RICHIE]

A few clarifications...

e-Richie my reference wasn't to you but Sachs. I knew you were the messenger. I apologize for the confusion since you and another thought it I must not have been very clear at all.

Jerk...I'm sure Sachs makes a fine bike and I would be the last to tell a custom builder not to build to his specs but mine. However I know it happens. People get Craig Calfee to build the bike to match an older Colnago, Eddy or whatever. I can't understand that but they do it.

I'm sure Sachs could care less if I want to buy his bike or not. I still think to make a flat statement that the only wobble on a bike is due to the pilot is ludicrous. I know it happened to me and it wasn't my error. It only happened with the one front wheel and I have ridden the hill before and since with no trouble at all. In fact I look forward to it as an opportunity to hit 50 for a change as there are not any cross streets to worry about.

I agree that the pilot could cause a shimmy but that isn't the only reason.


my pilot error light just went on.
what does this mean?
"e-Richie my reference wasn't to you but Sachs."

[Ken Robb]

Oh boy, I can hardly wait for Fly's answer to this one.

[Johny]

my pilot error light just went on.
what does this mean?
"e-Richie my reference wasn't to you but Sachs."

roy munson syndrome atmo

[Big Dan]

TWINS?......... :eek:

[Johny]

A few clarifications...

e-Richie my reference wasn't to you but Sachs. I knew you were the messenger. I apologize for the confusion since you and another thought it I must not have been very clear at all.

Jerk...I'm sure Sachs makes a fine bike and I would be the last to tell a custom builder not to build to his specs but mine. However I know it happens. People get Craig Calfee to build the bike to match an older Colnago, Eddy or whatever. I can't understand that but they do it.

I'm sure Sachs could care less if I want to buy his bike or not. I still think to make a flat statement that the only wobble on a bike is due to the pilot is ludicrous. I know it happened to me and it wasn't my error. It only happened with the one front wheel and I have ridden the hill before and since with no trouble at all. In fact I look forward to it as an opportunity to hit 50 for a change as there are not any cross streets to worry about.

I agree that the pilot could cause a shimmy but that isn't the only reason.


Rumor has that Sachs just hired e-richie to answer phone calls. Since e-richie has been working really hard and is also really talented that Sachs started to show him a trick or two of how to make steel bikes.

[OldDog]

I always wondered what that scribble on the top tube of a Sachs said...

[e-RICHIE]

I always wondered what that scribble on the top tube of a Sachs said...
it says "unprotected".

[jerk]

the jerk doesn't understand any of this.
jerk

[David Kirk]

the jerk doesn't understand any of this.
jerk


Who's on first?

Dave

[e-RICHIE]

the jerk doesn't understand any of this.
jerk

old dog means this (http://pg.photos.yahoo.com/ph/bobbesrs/detail?.dir=bfe4&.dnm=9355.jpg&.src=ph) scribble atmo.

[jerk]

old dog means this (http://pg.photos.yahoo.com/ph/bobbesrs/detail?.dir=bfe4&.dnm=9355.jpg&.src=ph) scribble atmo.

oh ok. as you were then.

jerk

[flydhest]

e-Richie my reference wasn't to you but Sachs.

I think we just need to say this out loud. Spelling doesn't count on the forum, right.

read: my reference wasn't to you, butt sacks.

[Dr. Doofus]

doof had a girlfriend with an unstable front end

then she started wearing underwear

[nick0137]

Or "my reverence wasn't to ewe, but Sachs".... Makes much more sense. To me at least.

[CalfeeFly]

I think I remember Roy... :p

With all the responses and confusion...mea culpa...it was Dr. Doofus...at least I think so... :crap:

How about I apologize to anyone I insulted except dear Mr. Sachs? That way I don't think I can go wrong. :confused: :D :help:

[Dr. Doofus]

With all the responses and confusion...mea culpa...it was Dr. Doofus...at least I think so... :crap:
:help:

what did doof do?

[flydhest]

what did doof do?

apparently, the young lady without knickers.

[e-RICHIE]

How about I apologize to anyone I insulted except dear Mr. Sachs? That way I don't think I can go wrong. :confused: :D :help:

that works here atmo

[Tom Kellogg]

Folks;

This is now pretty old, but it still applies, give it a click.
http://spectrum-cycles.com/615.htm

[e-RICHIE]

Folks;

This is now pretty old, but it still applies, give it a click.
http://spectrum-cycles.com/615.htm


tom
this:
"Tracking (or wheel and frame alignment) while not a primary contributor to shimmy, can help initiate it. The way this works is that a bike that tracks poorly, for whatever reason, is almost always under shear stress. At those times when the shear stress is relieved momentarily the frame, by definition, will go through one shimmy cycle. This can then be the start of a full shimmy development."
is almost in direct oppostion to what was in the vn article
that i cited in my cr post, noted here:
http://forums.thepaceline.net/showpost.php?p=202220&postcount=5
iirc, zinn and others have inferred that misaligned frames
could actually stave off a possible high speed oscillation.

[Big Dan]

I think we just need to say this out loud. Spelling doesn't count on the forum, right.

read: my reference wasn't to you, butt sacks.

Post of the month...imho.... :)

[fstrthnu]

Try putting some weight on Your front wheel when You are descending. No offense meant.

Fstrthnu

[gone]

my pilot error light just went on.
what does this mean?
"e-Richie my reference wasn't to you but Sachs."
(with apologies to the Monty Python crew)

I'm Richard Sachs and so's my wife!

[champlemon]

I think I remember Roy... :p

With all the responses and confusion...mea culpa...it was Dr. Doofus...at least I think so... :crap:

How about I apologize to anyone I insulted except dear Mr. Sachs? That way I don't think I can go wrong. :confused: :D :help:

I'm not e-richie, Richard Sachs or play either on TV... but my recommendation to Mr. Calfee Fly is that when he experiences any high speed wobbles on his bike, his car or his life... is to do something which at first seems counterintuitive, but which works* extremely well... CLOSE YOUR EYES AND LET GO OF THE HANDLEBAR!!!



*Works extremely well to rid this board of closed-minded fools... :rolleyes:

[Tom Kellogg]

iirc, zinn and others have inferred that misaligned frames
could actually stave off a possible high speed oscillation.

On perfect pavement, keeping the structure under tension with misalignment, will indeed help stave off wobble. Problem is that conditions almost always cause momentary release of that tension and the possible set up for a wobble. Bummer as always.

[e-RICHIE]

On perfect pavement, keeping the structure under tension with misalignment, will indeed help stave off wobble. Problem is that conditions almost always cause momentary release of that tension and the possible set up for a wobble. Bummer as always.


ya' see, that's what i don't get.
perfect conditions? high speed descents? speed oscillations?
pick 2 out of 3 at best. these mishaps occur in imperfect
conditions. what i mean is, who really "lives" at 50+ mph,
so much so that they're comfortable in that rarified world?
pros? perhaps. buy they don't experience this speed wobble
stuff the way the consumer base does. as a matter of fact,
i've never heard the term "shimmy" used in any race report
in all my years of paying attention.

people don't like to hear it, and i would be one myself, but
i believe it's rider related, this issue of oscillation. i don't
think the bicycle has to be perfect or imperfect. i simply think
there's a world of speed out there and once a certain breed of
cat enters it and has a moment of indecision, anything can happen.

folks descend the same hills in the same conditions on the very
same bicycles all the time, and once in a blue moon it shakes.
it's smart money to say it could be anything, but my bet is that
someone is in over his head at the wrong time in the wrong place.
how could this be if it's the same hill, condition, and bicycle you
may ask? oddly, a client asked me about this very issue yesterday
am while this thread was unfolding, and i likened descents to
dreams. we all have them. we believe we have some on a regular
basis, and that they are alike. but no two really are alike.

[William]

ya' see, that's what i don't get.
perfect conditions? high speed descents? speed oscillations?
pick 2 out of 3 at best. these mishaps occur in imperfect
conditions. what i mean is, who really "lives" at 50+ mph,
so much so that they're comfortable in that rarified world?
pros? perhaps. buy they don't experience this speed wobble
stuff the way the consumer base does. as a matter of fact,
i've never heard the term "shimmy" used in any race report
in all my years of paying attention.

people don't like to hear it, and i would be one myself, but
i believe it's rider related, this issue of oscillation. i don't
think the bicycle has to be perfect or imperfect. i simply think
there's a world of speed out there and once a certain breed of
cat enters it and has a moment of indecision, anything can happen.

folks descend the same hills in the same conditions on the very
same bicycles all the time, and once in a blue moon it shakes.
it's smart money to say it could be anything, but my bet is that
someone is in over his head at the wrong time in the wrong place.
how could this be if it's the same hill, condition, and bicycle you
may ask? oddly, a client asked me about this very issue yesterday
am while this thread was unfolding, and i likened descents to
dreams. we all have them. we believe we have some on a regular
basis, and that they are alike. but no two really are alike.

Well, I don't live there, but I visit as much and as often as I can. Taking "e"'s hint, I've never had a problem with shimmie on high speed decents. Even when on a frame that I could sit up and let go of the bars at 15 mph and have them start ocillating all over the place, at speed on a decent, no problem.

I've seen people have "shimmy" problems when they level their cranks at 9 & 3 when ripping down a hill. When it was suggested they move them to 6 & 12, and put a little more weight on 6, they smoothed out. A slight lowering of their COG.

Even weight distribution and technique atmo.


William

[e-RICHIE]

Even when on a frame that I could sit up and let go of the bars at 15 mph and have them start ocillating all over the place, at speed on a decent, no problem.

that's the difference that trail makes.
some bicycles steer oddly at slow speeds owing
to a low trail measurement, but win a race on that
effer and you'll have no problem doing this (http://pg.photos.yahoo.com/ph/bobbesrs/detail?.dir=8e6e&.dnm=1429.jpg&.src=ph) atmo.

[flydhest]

e-richie and TK,

Both of youse gimme a bike in 60 cm and I'll test them fully and give you an answer.

Howseboutdat?

[Grant McLean]

that's the difference that trail makes.
some bicycles steer oddly at slow speeds owing
to a low trail measurement, but win a race on that
effer and you'll have no problem doing this (http://pg.photos.yahoo.com/ph/bobbesrs/detail?.dir=8e6e&.dnm=1429.jpg&.src=ph) atmo.

E-meister, funny you should mention that.

I've noticed over the years that the two handed victory dance
is sometimes accompanied by the knees clamped to the top tube.

Those early carbon Look bikes like Jalabert used to ride seem to be
ones that I remember seeing the riders holding the top tube with their
knees as they cross the line.

G

[e-RICHIE]

e-richie and TK,

Both of youse gimme a bike in 60 cm and I'll test them fully and give you an answer.

Howseboutdat?


i'll give you a 40 and a 20.
the rest is up to you atmo.

[e-RICHIE]

E-meister, funny you should mention that.

I've noticed over the years that the two handed victory dance
is sometimes accompanied by the knees clamped to the top tube.

Those early carbon Look bikes like Jalabert used to ride seem to be
ones that I remember seeing the riders holding the top tube with their
knees as they cross the line.

G

are you now introducing the fact that speed wobble
also occurs outside of descents? that's a new one
on me.

[Grant McLean]

are you now introducing the fact that speed wobble
also occurs outside of descents? that's a new one
on me.

My recall isn't that good, but what I "saw" was a tour stage where
one of the bigger guys wins a sprint on a Look bike, and as he
crosses the line, the bars start to shake, and he grabs the top tube
with his knees, as his hands are in the air. Because they showed
the replay so many times a la OLN live coverage, waiting for the
Lance group to come in.... they played it over and over, that's why
it stuck with me.

-g

[CNY rider]

I've only had one episode of high speed shimmy. It was quite scary. I think it had a lot to do with me, and the air around me, but little to do with the bike. Let me'splain.

I was on my commuter (a Lyon, if it matters to anyone). I ride that bike to and from work probably 100 times a year. No wobbles, and I average 35 to 40 mph coming down my hill each morning.

One day my car was in the shop, so I had to go to the shop on my bike to pick it up after work. I'm heading downhill, wearing my messenger bag with about 5 pounds in it. It's a busy road to get to the repair place and traffic moves at 50 mph. I'm going down a long, sweeping hill, about 35 mph. A car passed me, and at the same time a UPS truck went by in the opposite lane. I could feel a sudden burst of turbulent air against the left side of my body. I very quickly built up a violent shimmy, to the point where I briefly thought about how I was going to ditch. Luckily I got my senses together, braked lightly, eased up my grip on the bars, and clamped my legs on the top tube. Shimmy over with.

Still riding that bike most days at 35 to 40 mph. No shimmy. I have to conclude it was the air turbulence from the passing vehicles, probably combined with the weight up relatively high on my back.

Just ATMO.

[Birddog]

are you now introducing the fact that speed wobble
It's happened to me twice, in fact the very first time. I had been riding about a year and was just finisheing a TT sligtly downhill, going all out and the bike atarted to shimmy just as I crossed the line. I didn't know what the hell was going on. Another time it was dead flat and a group of us started to really push it ( all out, but not a sprint if that makes sense) and the damn bike did it again. In this last case, it scared the other guys as much as it did me.

Birddog

[Tom Kellogg]

Richard:

You are right. My article is a theoretical examination of the factors that contribute to a bike being more prone to wobble. The first section concerning the rider addresses the point you make. It is indeed quite rare that a bike, apart from a specific rider, is a "wobbler." As I mentioned in the article, I am a bit sheepish about pointing to the operator, but in our experience (and yours) the rider is usually the biggest factor ... sorry. So, shoot the messenger (Richard, not me).

[e-RICHIE]

Richard:

You are right. My article is a theoretical examination of the factors that contribute to a bike being more prone to wobble. The first section concerning the rider addresses the point you make. It is indeed quite rare that a bike, apart from a specific rider, is a "wobbler." As I mentioned in the article, I am a bit sheepish about pointing to the operator, but in our experience (and yours) the rider is usually the biggest factor ... sorry. So, shoot the messenger (Richard, not me).


eh -
that occurred yesterday.

[sspielman]

eh -
that occurred yesterday.

That guy not only flamed E-Richie, but there was enough left to do Roy Munson as well....

[e-RICHIE]

That guy not only flamed E-Richie, but there was enough left to do Roy Munson as well....


better than the kingston trio atmo

[LegendRider]

better than the kingston trio atmo

The Merry Minuet

They're rioting in Africa
They're starving in Spain
There's hurricanes in Florida
And Texas needs rain.

The whole world is festering
With unhappy souls
The French hate the Germans,
The Germans hate the Poles

Italians hate Yugoslavs
South Africans hate the Dutch
And I don't like anybody very much

But we can be grateful
And thankful and proud
That man's been endowed
With a mushroom shaped cloud

And we know for certain
That some happy day
Someone will set the spark off
And we will all be blown away

They're rioting in Africa
There's strife in Iran
What nature doesn't do to us
Will be done by our fellow man.

[flydhest]

I will add that my one and only experience with a shimmy was on my very first CSi. It turned out that there was something wrong with fork tip. Serotta replaced that and all was dandy. This demonstrates both e-richie and TK's points.

Riders usually (almost always) cause the problems and only if you know that the rider knows what they're doing should you suspect the rig. Yes, that's shameless self-aggrandizement, why?

[Onno]

I can make my old steel bike wobble hard going downhill by giving the handlebar a a sudden shove. I can't make my Concours do this, no matter how hard I jerk the bar. This seems to me to be clear proof that in some cases at least, it's all about the bike.

[e-RICHIE]

Babies born addicted
Libya has a bomb
A killer for president
The rain forests are gone
It snowed in Malibu
Yosemite burnt down
Planes are flying
Right into the ground
But the thing that made me cry is when John Cassavetes died
The thing that made me cry is when John Cassavetes died
I cried when John Cassavetes died
That's what made me cry

[e-RICHIE]

I can make my old steel bike wobble hard going downhill by giving the handlebar a a sudden shove.
why would you do this?
i thought this thread was about
how it all happens unexpectedly.

[roman meal]

How prophetic.. And cute.

[Onno]

why would you do this?
i thought this thread was about
how it all happens unexpectedly.


Because the first time it happened to me on my steel bike, it was unexpected and truly shocking. I experimented at slower speeds to try to understand what was happening, and how I could avoid it. As soon as I got the new bike, I tested it in the same way, and was enormously gratified to feel how much more solid and stable it was. I don't know how else to describe the difference except that the steel bike felt wobbly in the front, and the Concours feels stiff and secure.

[e-RICHIE]

Because the first time it happened to me on my steel bike, it was unexpected and truly shocking. I experimented at slower speeds to try to understand what was happening, and how I could avoid it. As soon as I got the new bike, I tested it in the same way, and was enormously gratified to feel how much more solid and stable it was. I don't know how else to describe the difference except that the steel bike felt wobbly in the front, and the Concours feels stiff and secure.
i understand this - but if i got bumped in a
corner, i think my line might be altered somewhat.
isn't that the same analogy? one never gets bumped
in a corner the same way twice, yet if you're aware
that it could happen, your energy level is much more
ready to accept the consequences and react accordingly.

[CalfeeFly]

Gee I guess I was all wrong to say that I felt that the riders on this forum were of the stature that to say any shimmy had to be pilot error was not correct. I apologize to all those I insulted and to the various people who posted why I was wrong. If you folks feel that when a bike ridden by a forum member develops a shimmy on a high speed descent that it is their fault and only their fault then I defer to your judgment and expertise. (I am curious if those of you who believe this ever have a high speed shimmy will it be pilot error for sure?) :p

Again for me since every ride has me descending at least 35 to 40 mph and it only happened twice each time 5 years ago with the same front wheel I will go with the wheel being the problem. Since I'm not a flatlander and do higher speed descents every ride without any problems riding 4 to 6 thousand miles each year. I have a hard time believing that just by coincidence I made a "pilot error" on the two times I had one particular wheel on the front of my bike when it went over 46 mph. (It started at exactly that speed each time.) :banana:

[e-RICHIE]

most excellant atmo -

[Fixed]

bro a lot of people tell me i'm unstable . . .
cheers

[Brian Smith]

why would you do this?
i thought this thread was about
how it all happens unexpectedly.

It gets people off your wheel, yo!

[Orin]

Gee I guess I was all wrong to say that I felt that the riders on this forum were of the stature that to say any shimmy had to be pilot error was not correct. I apologize to all those I insulted and to the various people who posted why I was wrong. If you folks feel that when a bike ridden by a forum member develops a shimmy on a high speed descent that it is their fault and only their fault then I defer to your judgment and expertise. (I am curious if those of you who believe this ever have a high speed shimmy will it be pilot error for sure?) :p



Yeah it's pilot error, you failed to descend with a knee against the top tube ;)

BTW, the FAQ on shimmy at: http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html doesn't seem to have been posted yet.

The latest edition of Bicycling Science actually derives a formula for shimmy, though it's of little use as it needs data about the frame stiffness and so on which would be difficult to measure.

Orin.

[William]

While I was out enjoying my first 80 degree ride of the year today, this thread popped into my head. I contemplated it a lot. For me personally, descending is something I never gave much thought about. I've just always been good at it, as well as bombing into tight crit corners at speed. Just came naturally. But as I thought about it more, I critiqued myself as I rode along and on some good decents.
I rarely ever tightly grip the bars. On the drops, hoods or tops, my fingers are loose and just barely close around the bar. The only time I really close my fingers is when bunny hopping, hitting really rough pot hole pavement, or sprinting. I think this translates to me being very loose and controlled on the bike. Some of this comes from my MA training, always being loose and flowing with my movements (No, not karate kid with my arms in the air standing on one foot KIIIIIIIIAHHH! style :no: ).
Also, I never descend with my cranks parallel to the ground. I'm either cranking to top out the gear, or I'm in a 6-12 position, which side is which depends whether I'm sweeping into a right or left hand turn. It makes for a much more stable flow through the corners. To use an often maligned saying, "it feels like it's on rails".

Here's a little experiment for you. Next time your cruising down a curvy decent, try a few corner with your cranks parallel to the ground. Then try a few in the 6-12 position, pushing down a little on the outside crank (6 o'clock) and see what feels more stable.

I tried the parallel to the ground position in a few corners and it felt a little squirreley to me.

Any way, I've never needed to "knee" my TT. jmloo.

William

[e-RICHIE]

none of this science stuff (http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html ) ever made much sense to me.
in a private email with another builder with whom
i was discussing this issue, i wrote:
what i don't get is that kids on stingrays deliver papers while
riding "no hands", and spaniards descend the pyrennes on $200
orbeas and live to tell about it. everything in between covers the
rest. (of types of bicycles)
i believe there is a rider comfort zone and it dictates what
the bounderies for each frame's limits are.

[Ray]

While I was out enjoying my first 80 degree ride of the year today, this thread popped into my head. I contemplated it a lot. For me personally, descending is something I never gave much thought about. I've just always been good at it, as well as bombing into tight crit corners at speed. Just came naturally. But as I thought about it more, I critiqued myself as I rode along and on some good decents.
I rarely ever tightly grip the bars. On the drops, hoods or tops, my fingers are loose and just barely close around the bar. The only time I really close my fingers is when bunny hopping, hitting really rough pot hole pavement, or sprinting. I think this translates to me being very loose and controlled on the bike. Some of this comes from my MA training, always being loose and flowing with my movements (No, not karate kid with my arms in the air standing on one foot KIIIIIIIIAHHH! style :no: ).
Also, I never descend with my cranks parallel to the ground. I'm either cranking to top out the gear, or I'm in a 6-12 position, which side is which depends whether I'm sweeping into a right or left hand turn. It makes for a much more stable flow through the corners. To use an often maligned saying, "it feels like it's on rails".

Here's a little experiment for you. Next time your cruising down a curvy decent, try a few corner with your cranks parallel to the ground. Then try a few in the 6-12 position, pushing down a little on the outside crank (6 o'clock) and see what feels more stable.

I tried the parallel to the ground position in a few corners and it felt a little squirreley to me.

Any way, I've never needed to "knee" my TT. jmloo.

William
I had a nice 80 degree ride today too - nice to feel the legs loosen up in the heat. Ran into a forum member too, Red CDA was the bike and the handle was similar - PM me if you get a chance.

Anyway, you should never start thinking about how loose you are on descents - it'll make you tight. Like someone asking you whether you breathe in or out on your backswing - this could bring Tiger Woods to his knees. If you're loose, good on you. I'm almost always loose too until conditions get too extreme, which is where the problem usually presents itself. Either too steep (which requires a lot of heavier than usual braking), too windy, poor road conditions, or some great combination of all three. And, oh yeah, being cold doesn't help either. It's when these conditions are present and something starts going FUBAR on me that I tighten up and that's when I've experienced shimmy. Hasn't happened often, but I've always been able to identify the culprit (me).

As far as descending in the 3-9 or 12-6 position, to me it all depends on the road conditions. If its smooth enough, I go 12-6 with the outside foot down and yeah, it handles a bit better. But when the road's rough or bumpy, I keep 'em at 3 & 9 so I can keep both knees well bent and ready to absorb the shocks. I've done some reasonably fast descents at 3 and 9 without any problems - I think it's just a matter of getting used to it.

-Ray

[William]

I had a nice 80 degree ride today too - nice to feel the legs loosen up in the heat. Ran into a forum member too, Red CDA was the bike and the handle was similar - PM me if you get a chance.

Anyway, you should never start thinking about how loose you are on descents - it'll make you tight. Like someone asking you whether you breathe in or out on your backswing - this could bring Tiger Woods to his knees. If you're loose, good on you. I'm almost always loose too until conditions get too extreme, which is where the problem usually presents itself. Either too steep (which requires a lot of heavier than usual braking), too windy, poor road conditions, or some great combination of all three. And, oh yeah, being cold doesn't help either. It's when these conditions are present and something starts going FUBAR on me that I tighten up and that's when I've experienced shimmy. Hasn't happened often, but I've always been able to identify the culprit (me).

As far as descending in the 3-9 or 12-6 position, to me it all depends on the road conditions. If its smooth enough, I go 12-6 with the outside foot down and yeah, it handles a bit better. But when the road's rough or bumpy, I keep 'em at 3 & 9 so I can keep both knees well bent and ready to absorb the shocks. I've done some reasonably fast descents at 3 and 9 without any problems - I think it's just a matter of getting used to it.

-Ray

True, I never think about it. I just did on yesterdays ride to monitor what I do.

Ok, in hindsghted thought (like I said, I never think about it), I also use the 3-9 on rough pavement to asborb shock with my knees and hovering my butt just off the saddle. But I'm certainly not bombing when I do that. If I'm all out, it's 6-12 all the way.


William