Help - bike is shaking on a downhill

[Willy]

This just started and I am hopping someone on this forum can help me.

Going down a long hill by our house as I start to go past 30 mph ( I know that is slow for some of you) the bike starts shaking violently- front wheel and handlebars seem to want to go left and right all at the same time. I am barely able to keep control enough to stop. First I thought about the brakes and tired to only use the back brakes - that didn't change anything. The rear wheel area seems stable.

My bike is a Serotta (of course) TI with a Kinesis Carbon 2 fork and King Bearings. I have put 15,000 miles on it. My corrections have been to rebalanced the wheels and put new tubes and tires ( 25 Michelin Krylons).

Your help is appreciated - its scary to ride with this in the back of my mind.

[Louis]

Oh goodie, another shimmy thread. These always have a clear-cut answer ;)

[mflaherty37]

i suggest to

pinch the top tube with your knees and bend your elbows.

[stevep]

let someone else try the same hill on the bike.
see what happens.

[Erik.Lazdins]

its scary to ride with this in the back of my mind.

This may be contributing to the problem in my opinion.

On other hills that you love does this happen?

[Ginger]

Yep, the one and only time my Kirk ever shimmied was when someone psyched me out about a hill...Once I saw it wasn't that huge, nor steep of a hill, the shimmy stopped.


That and I'd inspect the steerer on your fork and the fork itself.

[Ken Robb]

yep--we've beat this horse to death--several times. Try a search of the archives for shimmy and read away. I have had this problem to varying dgrees on a few bikes but never any Serotta. It is sometimes just about the rider/bike interface in my experience. The bikes I owned where I couldn't stop it I sold. As far as I know they didn't shimmy for the buyers. I made them all try a fast downhill before I took their $$$.

[Peter P.]

Don't feel bad, Willy. Last week, I had my bike go into a shimmy. This bike has never exhibited handling problems in the 11 years I've owned it. What happened is, I was heading downhill and hit an unseen object in the road. It jolted me but good, and the bike immediately began to shake. The only way I could bring it under control was to scoot off the back of the saddle and apply the rear brake to scrub some speed off. Once my speed reduced, the shimmy disappeared and never reoccurred.

Explain what you mean by "rebalanced the wheels".

Make sure your headset is adjusted properly and not pitted. (I know you said it's a King, but check anyway)

Check both hubs for loose axle bearings or broken axles.

Make sure both wheels are installed correctly in the frame so that they are straight and centered.

Sorry, but you're going to have to test the bike by going down the same hill at the same speed to see if it reoccurs.

If it does, try borrowing another set of wheels and repeat the experiment.

Also, check the frame and fork closely for cracks.

If you can ride the frame no-handed without any problems, it's safe to say the alignment is good. Again, yeah; I know it's a Serotta but check anyway.

Sometimes all you need is the perfect storm of pavement conditions, speed, and position on the bike to initiate shimmy. Your experience may have been a freak occurrence. Report back if the problem is still present.

[Ginger]

Did I mention check the steerer?

People don't like to pull their fork and check their steerer...but it isn't time wasted if you have a question like that.

[saab2000]

My CSI (Crime Scene Investigator) shimmies. I will try another set of wheels before I pass total judgement, but the fact is that the front end is simply kinda flexi. I know from whence the OP speaks, though I don't get freaked out about it. If it's really bad simply put your knees against the top tube. That'll stop it. Frankly, just keeping my hands on the bars stops it. It only happens while riding no-handed. But the front end is decidedly 'light' and prone to high frequency oscillations. None of my other bikes does this.

[Sandy]

I agree with Ken. Do a search on the following words- "shimmy" and "wobble". There are numerous excellent threads on such. If you do not know how to do a search, we will be glad to tell you how.


Sandy

[Fixed]

i went to utah my bike shook too
cheers :beer:

[saab2000]

i went to utah my bike shook too
cheers :beer:

I was gonna say, you don't have many hills down there in Florida!

[e-RICHIE]

Do a search on the following words- "shimmy" and "wobble".


Sandy
atmo -
http://serotta.com/forum/showthread.php?t=17052&

http://serotta.com/forum/showthread.php?t=17263&

[RPS]

Did I mention check the steerer?

People don't like to pull their fork and check their steerer...but it isn't time wasted if you have a question like that.Did you have a steerer failure?
Don't recall that being mentioned before.

[RPS]

My CSI (Crime Scene Investigator) shimmies. I will try another set of wheels before I pass total judgement, but the fact is that the front end is simply kinda flexi. I know from whence the OP speaks, though I don't get freaked out about it. If it's really bad simply put your knees against the top tube. That'll stop it. Frankly, just keeping my hands on the bars stops it. It only happens while riding no-handed. But the front end is decidedly 'light' and prone to high frequency oscillations. None of my other bikes does this.Saab, the shimmy you describe sounds different to me than the high-speed wobble Willy described. Regardless of what name we use to describe these two types of events (shimmy, wobble, etc.), I’m certain the dynamics are different. There are similarities, but the underlying causes are not the same.

[Grant McLean]

For years i've been hearing people's experiences, so let me start by saying that I
don't think there is a single cause of all shimmy experiences since the beginning
of recorded time... so one set of variables will not satisfy everyones problem.

It does seem as if a laterally flexible front triangle seems to increase the
possibility of shimmy.

There are at least two camps:
the death bikes that almost always do the shimmy under the same conditions,
and the other -a once in a million shimmy. I think the second is far more common.

-g

[saab2000]

That may be. And like I said, I'll reserve final judgement until I try the bike with some different wheels. But that doesn't change the fact that I can wobble the bike myself with just some hand movements on the bars. I am a reasonably smooth rider and it doesn't really affect me and the riding I do on this bike, but my other Serotta does not do it at all.

The headset is tight enough and doesn't knock or anything like that. The wheels are not perfect.

Anyway, it's not a huge issue. And only really manifests itself if I sit up no-handed. But I can do that with the knees on the top tube too and still steer OK.

Changes are coming to this bike, including a different set of wheels. It is a good bike, but it does wobble/shimmy. I like the smooth ride. I like the aesthetic. But it is not as stiff in the front as it is in the BB area and rear triangle and this might lead to what I am talking about. Also the steering is not as race bike-like as I would desire. And it could even be argued that it's too small for me. But as a member of the 57 CM club there's no going back.

And yes, that's a 13.5 cm stem. :D

And one more thing... That hideous water bottle cage has been removed and there WILL be some King SS cages installed. After all, if you're not looking good, you're looking bad.

[Ken Robb]

I don't care what a bike does when I ride no-handed. They weren't designed for that. I think we are discussing shimmy w/both hands on the bars. The OP said it happened at 30+ mph and I don't think he was riding no-hands at that speed. well maybe if he had a New Departure brake. That reference will test to see how old you are. :beer:

[Louis]

The OP said it happened at 30+ mph and I don't think he was riding no-hands at that speed.

I've seen DD88 ride no-hands while we were doing at least 40 mph. He called it his "alignment test" ...

[Ray]

There are at least two camps:
the death bikes that almost always do the shimmy under the same conditions,
and the other -a once in a million shimmy. I think the second is far more common.
Yep. I had one bike that shimmied any time I got to 36 mph and stopped if I rode through it to 39 mph, but usually I slowed down instead. Since then, I've had many bikes and some of them have gone into the death wobble once or twice under unusually horrific conditions, but nothing reproduce-able. I usually just relax and, if that doesn't work, clamp the top tube with my knees. That's ALWAYS worked. It really helps not to freak out when it happens but that's easier said than done when it gets really intense at high speed. In which case, clamp the knees.

-Ray

[97CSI]

My CSI (Crime Scene Investigator) shimmies. I will try another set of wheels before I pass total judgement, but the fact is that the front end is simply kinda flexi. I know from whence the OP speaks, though I don't get freaked out about it. If it's really bad simply put your knees against the top tube. That'll stop it. Frankly, just keeping my hands on the bars stops it. It only happens while riding no-handed. But the front end is decidedly 'light' and prone to high frequency oscillations. None of my other bikes does this.Interesting. I use a Record headset in my CSI and routinely hit 40+ on downhills without a hint of instability. Of course, I've never tried it with my hands off the bar. Trying another set of wheels is also where I would start.

[saab2000]

Interesting. I use a Record headset in my CSI and routinely hit 40+ on downhills without a hint of instability. Of course, I've never tried it with my hands off the bar. Trying another set of wheels is also where I would start.

The headset on mine is a Dura Ace. The fork rotates easily 360 degrees with no looseness or binding. I think the headset is not the problem. The wheels are imperfect, I know that. But the front end is simply looser somehow than on my other bikes.

Anyway, this bike is likely to get "Ergo-ized" pretty soon and will have better wheels on it. I hope that helps somewhat. I do like the bike. But would like to like it even more.

[Tobias]

This subject gets recycled more than any other. :rolleyes:

[mister]

perhaps this will be interesting. it will atleast give you some ideas on what to do with you experience this going downhill...

http://davesbikeblog.blogspot.com/2006/08/shimmy-re-visited.html

[Ken Robb]

I had Trek aluminum frame and fork that shimmied at 32mph and I could do nothing to stop it. The dealer said the frame was within spec (+/- 2mm.) from ffront axle to rear dropout on each side. I don't know where he got those specs.

We swapped wheels for top-o-the line- Rolfs and the speed at which the shimmy started moved up to 34mph and I still could not stop it.

The mechanic rode it and said he could feel some incipient shimmy but it went away when he rested a knee on the tt.

The guy I sold it to couldn't make it shimmy period. We were similar in height but he weighed 30 lbs. less.

Sme shimmy with my Litespeed and Lemond Zurich but both could be stopped by the knee trick.

Zero shimmy with 1981 Nishiki Pro, Legend, CSI, Kirk Terraplane, Rivendell Rambouillet and Allrounder, Hampsten Strada Bianca. Go figure?

[mike p]

Saab I'm no expert, but I love old steel bikes and have ridden many that aren't as stiff as your CSI (front to back) and no problem with shimmy. I don't believe it's the frame (unless it's been damaged). Look for something else. I ride the same size and currently have a CRL, classique, RB-1 and Giordana. I'm sure your CSI is as stiff or stiffer than any of those.

Mike

[victoryfactory]

Am I nuts? Or do all shimmy prone bikes have one thing in common?
Large size frames.
I ride a 52cm - 53cm frame. I've never experienced shimmy in any of
the many bikes I've owned. Have any of you other short people? (I'm 5'8")

It seems like every shimmy story has a tall person in the starring role.

VF

[Louis]

Am I nuts? Or do all shimmy prone bikes have one thing in common?
Large size frames.
I ride a 52cm - 53cm frame. I've never experienced shimmy in any of
the many bikes I've owned. Have any of you other short people? (I'm 5'8")

It seems like every shimmy story has a tall person in the starring role.

VF

I've never seen any numbers, but I bet you're right. It may be that larger frames are not as dynamically stiff as smaller frames (for the vibration modes that contribute to the problem), possibly making them more likely to shimmy.

[Birddog]

It seems like every shimmy story has a tall person in the starring role.

Nope, I've had several frames in the 54 to 56 size range that have had shimmy. I DO think it is more common in bigger sizes. Back when OLN had that show where they tested bikes with Leonard Zinn and Bob Roll, almost every bike under Leonards arse would shimmy at speed. It should be noted that they were always off the shelf bikes and they were all too small for him. One bike I used to own never shimmied. It was a Softride.

In regards to Saab's shimmy, I also have a CSi (steel fork) that shimmy's when I ride no hands. It is pretty mild and always starts at about 27 mph. All I have to do to stop the shimmy is lay one finger on the bars and it immediately goes away. I don't even have to put much force on the finger. I've never bothered to switch wheels around to test the bike.

Birddog

[97CSI]

The headset on mine is a Dura Ace.Yep.....that's likely the problem. You need to make the leapmo to quality. Campagnolo quality, that is. Just kidding, of course. Still would suspect the wheels first. That said, its all Campy for my CSI.

[Willy]

I have come to the conclussion that most of you were right by blaming the rider. I had an accident about a year ago and two weeks ago I tripped and fell on my face running. I have become very paranoid and per your comments - I can see that my fear has been transmitted into how I ride the bike and thereby creating the shimmy.

I went out today and it's going to take a little time to get confortable again.

Thanks for the comments, they were right on.

[StefanZ]

I never had experienced front end shimmy until about two years ago when I rode my newly built Douglas Vector (an aluminium frame with carbon rear triangle) at about 30 mph down a hill. Granted, I was sitting up on the bike with no hands on the bars. At any rate, after I checked the bike over (headset etc) I tried again and could reproduce the situation. The immediate help was, as broadly discussed here, put hands on bar (not too tight) and (if desired) clamp top tube with knees. Once I figured all this out, shimmy was no big deal, and I enjoyed riding the vector (at speeds downhill up to 50 mph). Still, the issue bugged me and I researched it; I decided that it is a shortcoming mostly of the frame, i.e., to twisty in the front with insufficient damping. I decided to experiment to increase the torsional stiffness of the frame in the headtube downtube and top-tube area by injecting high density PU foam. This is, btw, a technique used by Bianchi (or at least in the past they did) to stiffen up their BB in reparto corse level bikes. Using aluminum tubing I practiced and convinced myself that I could safely try this with the front-end of my bike. I injected two slugs of about 15-20 cm length through the bores from the headtube into the down and top tube. The foam expanded and bonded with the tubes; by tapping on the tubes you can assess how far down the slug went and bonded with the tubes. This worked great to ameliorate the shimmy problem; again, hands-off sitting up on the saddle going downhill at 30 mph the bike now wants to start a shimmy (one can also knock it briefly to start an oscillation) but it now stops on its own after a few cycles. The foam has likely increased the torsional stiffness, but foremost added the ability to dampen vibrations. The weight added by this procedure is only about 30 g, and well worth it. Caveat, however: PU foam binds ferociously to almost anything, particularly if it's moist (you can pre-moisten the area where you want to get fast cure and bonding), so be careful. Also, it is nearly impossible to remove PU foam chemically after it has bonded and set.

From Bianchi's website:
Technology Solutions
Structural Foam Injection is a 2-component non-toxic foam developed by Henkel Spa Surface Technologies and patented by Bianchi for specific cycling applications, i.e., as a tube strengthening material. The results obtained through the introduction of SFI have been noteworthy: a weight increase of only 20 grams yielded a 15% improvement in stress resistance, while resistance to fatigue doubled in the bottom bracket area. All this was made possible by the special properties of this foam, which is able to distribute the loads evenly, avoiding fatigue build-up in high stress areas and in welded parts whose composition has been thermally altered.

[victoryfactory]

I decided to experiment to increase the torsional stiffness of the frame in the headtube downtube and top-tube area by injecting high density PU foam. This is, btw, a technique used by Bianchi .


Shaking problems in machinery can often be traced to components which
start to vibrate like a tuning fork under certain use patterns.
Damping those vibes with foam sounds like a very cool idea.
What you might end up with is a frame with the best qualities of steel
and carbon.

BTW, has anyone experienced shimmy on a carbon frame?
just wondering....

VF

[Cheapskate]

How about you just relax and enjoy the shake? Think of it as free Starbucks. With refills.

[regularguy412]

Shaking problems in machinery can often be traced to components which
start to vibrate like a tuning fork under certain use patterns.
Damping those vibes with foam sounds like a very cool idea.
What you might end up with is a frame with the best qualities of steel
and carbon.

BTW, has anyone experienced shimmy on a carbon frame?
just wondering....

VF

I was riding with my buddy last year. He was on his 2004-2005 model carbon Specialized Roubaix. We went down a steep hill on a loop that we do all the time. His bike developed serious speed wobble. I didn't know it until well after I made it to the bottom. He was behind me a little at the top. When I reached the bottom, I looked around and he was wayyyyy behind me ,, something on the order of a quarter mile.

As it turns out, he had been stung by a wasp on his right hand earlier in the day. He suspected that since he was not applying equal pressure to the bars because of the swelling, that it likely induced the wobble. Now he's a bit gun shy of descending at speed. He raced for over 15 years, so the shimmy was a pretty big deal. I don't think it was the bike, per se, but I'm trying to get him to sell the carbon and get back on steel. He literally rode his Moulton Fuso until he could push his finger through the middle bottom of the top tube. That bike never shimmied.

Mike in AR:beer:

[Dan Le foot]

You didn't say what bike you had. All ti bikes are not created equal.
My 1st Serotta was a lower end Classique ti. Shimmied at 30 mph.
I moved up to a Legend. No shimmy at any speed.
Great excuse to get a new bike. :beer:
Dan

[Der_Kruscher]

Not to rehash a (possibly) dead topic but I have a related question that I don't think has been covered. A week or so back I experienced a wobble while decending on a bike that I've never had stability issues with. I have/had been riding some rough roads that included bombing over some cattle grates and whatnot but no crashes on the bike. Anyway, same story as everyone else, I hit about 35mph and the bike goes into a wobble. I slow down and the front end still feels a little squirrely. The day before, my headset had loosened up (also a first but the roads were rough enough that the front derailleur hanger screws on my Giant TCR1 aluminum began backing out) so I imagine some sort of steerer tube damage on my Easton EC90SL fork. Anyway, shop checks the fork out and there are no cracks or anything. Front wheel is fine, no broken axel or anything. Still, the front end feels flexy to me...probably paranoia as the wobble freaked me out pretty well. So, my question is; could a swap to a stiffer bar/stem combo help matters out? Somehow it seems to me that this may help but wobble problems may be more profound in nature. Oh, for reference I currently am riding a Reynolds Ouzo Race stem and Easton EA70 bars which always felt fine to me before.

[RPS]

So, my question is; could a swap to a stiffer bar/stem combo help matters out? Somehow it seems to me that this may help but wobble problems may be more profound in nature. Oh, for reference I currently am riding a Reynolds Ouzo Race stem and Easton EA70 bars which always felt fine to me before.It’s a complex multifaceted problem that is difficult to diagnose because the underlying cause is not understood well. Typical procedure involves a lot of guessing. In my opinion its possible changing bars and stem will make a difference but the probability that it will correct the issue completely is minor unless either is damaged.

[Der_Kruscher]

Thanks for the response, RPS. I may swap the bars and stem just to add a measure of confidence even though mechanically there may not be any real issue with either.

It’s a complex multifaceted problem that is difficult to diagnose because the underlying cause is not understood well. Typical procedure involves a lot of guessing. In my opinion its possible changing bars and stem will make a difference but the probability that it will correct the issue completely is minor unless either is damaged.

[PSC]

I have had some problems on the chip and seal roads that I use in my area. After today I am convinced it is not the bike, but the rider (me). I have changed every component and frame and I still have gotten the shimmy at one time or another. I have been experimenting and basically self inducing the shimmy to see what causes it. What I think I was doing is locking out my elbows and getting off the saddle at the same time or a combination of both. I have been riding for 30 years and have never experinced this problem before (FYI, I have just resently started riding these rough roads). I have also noticed that when a truck passes me from the opposite direction a wobble seems to develop again, I think that I was tensing up and locking my elbows, and with the passing truck wake a wobble developed. Today I was going downhill on the same chip and seal roads and just made sure that my elbows were bent and that I was relaxed. When I found my butt raising off the saddle I could feel some instability, but as soon as I sat down it disappears. What I guess that I am getting at is that is probably is not the bike, but the rider (even though I don't want to admit it). I am going to just stay relaxed and let the bike go down the hill no matter how crappy the surface or truck wakes effect my handling. Stay relaxed, elbows bent and butt on the saddle.

[ridemoreoften]

I have had it happen once and I got rattled before, anxious about the speed. Not the bike but me. Go slow early in the season and increase speed as the season goes on. Also happened to a good buddy of mine. My IMHO theory. Best of all, you were out riding.

[Willy]

Since I started this discussion - let me add my new experience. I went back over the road were this wobble started this past weekend to try out what was suggested here. Now I am sure it was not the bike but myself. I kept my knees very tight to the frame (wondered if I was going to damage my ... ) and my elbows in - as long as I did this there was no wobble. I am still skitzy about the road but am confident that I can work on becoming at ease in the future - Thanks for the advice.

[Der_Kruscher]

The weird thing for me is that I've been decending pretty well this year. I'm not super fast downhill but confident enough and can occasionally drop some folks. In retrospect I think that a gust of wind may have started the wobble in my case and then nerves took hold as I imagined my steerer splintering into a million pieces. The unmentioned downside of compact frames is that while they're sexy they don't give you much to grab with your knees :)

[Birddog]

I think that a gust of wind may have started the wobble in my case and then nerves took hold as I imagined my steerer splintering into a million pieces.
I'm unfortunately an experienced "Wobbler". In my experience the wobble/shimmy can be set off with a wind gust coupled by a tightening of the grip or sudden lateral movement. Couple this with rougher chip and seal roads and you have the recipe. As best I can recollect, most of my shimmy times have been triggered by road imperfections, i.e. cracks, bumps etc. My own personal experience is that the grip and stiff elbow position is the biggest contributor. A little relaxation goes a long way, although on at least one occasion, nothing seemed to work. As a precaution, I sometimes have my knees right up near the top tube just to be prepared. At other times I just alternately press one knee to the tube on twisty descents.

One day several years ago, I tried to isolate the cause on a long, gently curvy, fast 45-50 mph descent. I could make the bike alternate between shimmy and steady simply by applying and then releasing a "death grip" on the bars. That was an eye opener.
Birddog

[e-RICHIE]

My own personal experience is that the grip and stiff elbow position is the biggest contributor.
Birddog
gandino gets it atmo.

Richard is a genius. Follow his advice.

[Fixed]

my bike shakes when I get it down off the hooks
cheers

[rpm]

In the last Bicycle Quarterly Jan Heine tossed out a couple of ideas. One is that a Stronglight roller bearing headset could cure shimmies, mentioning how it cured the shimmy on a couple of bikes.

The other is that increasing the diameter of the top tube won't help shimmy. I'm not so sure about that one. On big frames, which are the ones prone to shimmy, a larger diameter top tube may make the bike torsionally stiffer and thus reduce shimmy. I ride big frames, and I got shimmy on a couple of bikes with narrower top tubes, and didn't on wider ones.

One last thought is that a Kinesis carbon fork may be suspect. I had a bike that had a Kinesis carbon fork and a tendency to wobble that got all better when I installed a Wound Up fork.