Hey all,

 I took my ST on a descent for the first time at 32mph and the front end wobbled. Needless to say, I slowed down. I had some pretty good side winds at the time. Do you think it's due to the down tube/forks acting as a sail in the wind?

Speed wobble (aka death wobble). Google those two terms and you'll get a whole heap of information. Unfortunately, a lot of it is proffered by people who've never experienced speed wobble, but can't resist pitching in. Unusual, that, for the internet.

First, let's be clear about what is it we are talking about. Speed wobble is an uncontrollable front end wobble of the fork, steerer & bars, that can appear from nowhere and become (very quickly) so violent that you think you're going to be thrown off your bike. Usually it happens at speed on a descent (although it happened to me once on the flat when a moped I was drafting behind brake tested me pretty hard). Scares the living bejesus out of the rider. I used to get it on a Giant TCR I once had. Every descent, bang on 54 kmh. That's speed wobble. Any pale imitations not accepted.

Secondly, let's get straight to the answer: how do you stop it? There is, AFAIK, tried and tested immediate remedy. Lift your backside ever so slightly off the saddle, and/r clap the top tube between your knees. I have heard of a longer term solution as well: grip the handlebars very lightly. This one is obviously counter-intuitive when they are shaking out of your grip, but the idea is not to grip them too hard in teh first place. This, I gather, is a solution that a rider needs to work on over time to perfect.

Thirdly, it's all very well treating the symptons, but what's the cause? There are a million and one ideas floating around the internet. My favourite (wrong) one is a loose headset. What is obvious (at least to me) from the symptons is that speed wobble is a resonant vibration in the bike. Unlike a standard vibration, which dies away over time, a resonant vibration grows in amplitude over time: each input back into the system feeds the vibration. The "solutions" above suggest that the vibration is bouncing off the rider's contact points, and being amplified by them: remove the reflective surface (the backside) and the vibration dies away.

The question is what is feeding it in the first place? The obvious place to start is a moving part rather than a static part. My personal ideas (which I have never tested with any sort of rigour, or proved to be accurate, so take with a pinch of salt) concern the front end: (a) is the front wheel evenly placed in the fork dropouts? Spin a vertical wheel in your hands, holding by the QRs. Spins nicely when its vertical. Now tilt it off vertical slightly. Big forces at work - you can feel them immediately. (b) is the fork even? There's a fork manufacturer (can't remember which one) that has a section on its website that explains that speed wobble is attributable to the arms of a fork not being precisely the same length (which is their unique selling point). This fits in with (a). (c) Are the handlebars pointed forwards? This is the first think I remember fixing on a bike when I was a kid. You look down as you're riding in a straight line, and notice that you bars are pointed ever so slightly to the left or right. Never seems quite as easy to get them true as it should be. But in principle, I suppose if you were unwittingly trying to get the bars true on a descent with rigid arms, you'd push the front wheel out of dead ahead. (d) (a longshot, this one) one hand is exerting more pressure on the bars than the other. Again, another way of creating a marginal wheel imbalance.

Now maybe the majority of riders suffer all of these problems, but the vibrations that they each create serve to cancel one another out, so the vibration never gets going. I have no idea.

One final idea (again, never tested, so pinch of salt) is this. The resonance is of part of the frame. However, it seems to me that the resonant frequency may depend on the dimensions of the entire structure, and the rider weight (eg an 80 kg rider gets speed wobble at 55kmh. Would a 50 kg rider get it at the same speed, on the same frame, identically set up?). If so, then a small change in set up *may* adjust the resonant frequency. I have in mind swapping the stem for the next size up, or adjusting the saddle height marginally.

Hope that helps. Just remember: just because you read it on the internet doesn't mean it's true.

I'd also check your headset, from past experience even a slightly loose headset can cause the terrifying front end wobble.

Hope this helps.

Allen.
 

That's a lot of info there, greg66. I was told the cause could also be a loose headset. I'll go over the bike and keep what you said in mind when I ride again.

 Thanks

 

Perhaps I should explain why I'm sceptical about the loose headset theories. I don't doubt that a loose headset could cause a speed wobble. I do doubt that all speed wobbles are caused by loose headsets.

On the TCR that I had, I could ride along on the flat at say 35 kmh, and give the handlebars a shake at around speed wobble frequency. I could feel that the vibration I was putting into the frame wasn't dying away as it should; the frame *wanted* to keep vibrating. By contrast, when I've done the same thing with subsequent bikes that I've had, I can feel the vibration dampening down immediately. More to the point, look down when it's happening: the bars, stem, steerer, head tube and front end of the down & top tubes are all swaying. But I couldn't feel any freeplay in the headset, or in the steerer within the head tube (I've had a loose crown nut on an old quill stem set up, and I know what a loose front end feels like when it's not tightened down; this is something different).

I pored over the front end of that TCR and there was nothing loose anywhere. But the speed wobble was still there. And I can't help but think that if the headset was loose, you'd be able to feel that by simply pulling on bits of the front end while the bike was stationary. Or hear it by bouncing the front wheel n the ground. Again, not present in the TCR.

Hopefully Gerard will be along at some point to shed some light. I seem to recall that he's expressed views about speed wobbles before on slowtwitch. Since he's the engineer, he's the one to listen to, not me.

Good luck with getting to the bottom of the problem. It's a pretty horrible sensation, and it can undermine your confidence in the frame pretty easily, IME.

I have seen several bikes with wobble problems, on an occasion it seems to be a who knows answer.  On several of the occasions it came from rider/bike changes/customization.  examples someone who is real tall/short for there bike(wrong size bike), is not going to properly weigh the bike putting to much/little weight on the front end.  Changing the stem to long/short for the same effect.  changing fork rake, giving to long or short of trail.   I have seen this with custom bikes when designer/ rider did not see eye to eye also. 

When it could not be fixed by unchanging these problems then it seems like a design problem, maybe vibrations, etc.  that would stop when putting a hand on the top tube or pinching it with your knees,  when this is the case I refer them to the manufacturer,  usually no fix and it becomes there- tool around town bike.

that being said I have never had a customer have any complaints on how there soloist team rode.

sam

I tightened up the headset a little and went for another ride. I ended it with the same descent (32mph the first time) that gave me the front end wobble the other day. I stayed in the drops and in the saddle again to see if anything changed. I got to 34mph (very little wind, not sure if that mattered in this case) and I had nothing but smooth steering.   I guess the headset needed a little tightening. I'm still gong to swing by the shop so they can check the bike over anyway since I've got about 90 miles on her.

 Thanks guys for the input. This is a great Cervelo community.

 

Bang goes my credibility!

Greg,

Your credibility is still intact as you wrote - "I don't doubt that a loose headset could cause a speed wobble. I do doubt that all speed wobbles are caused by loose headsets".

And my experiences bear that out:

Litespeed Ultimate - definitely no play in head set yet bumpy descent with cross-wind = death-wobble assured!!  This bloody bike gave me nightmares and I gave up trying to fix it after two years (new forks/headset/wheels) !!  It's now my winter beater (Titanium has it's uses!)
Abici (who remembers them!) XLR8R - never had an issue until my USE stem crushed the carbon steerer and left play in the headset - wobble, wobble, wobble.  Don't think USE was at fault here, this was my fault over tightening the goofy offset clamping mechaninsm.
R3SL - It has wobbled once (badly!!).  This was my very first race in June this year just a few days after building the bike up...  I couldn't find any headset wobble but I dismantled/reassembled to try and gain peace of mind.  Since then, all has been well and I've been up to 80kph on descents before chickening out.

The only cure that worked for me when it happened, is to clamp the top tube with my knees.  Easy to write here, much more difficule to remember and execute when your eyes are being shaken out of their sockets and you're thinking about that next hairpin coming up all too rapidly...

There is also much to be said for trying to relax on descents.  I'm a nervous descender and so this is naturally a challenge for me, but the bike feels much more fluid and natural if I try to avoid hanging onto the bars with a death grip ;-)

Hope you get cured.

PaulR

 

Hi Paul,

I had a Litespeed Tuscany, I didn't think the front end was that bad but now I've got my R3-SL I can't believe how much better the Cervélo is. The Litespeed was very vague on descents were as the Cervélo just feels fantastic. The bizarre thing is though that on the flat the front end of the Litespeed felt nervous despite not being that stiff while the R3-SL despite it's front end stiffness has no such problems.

Oh and why did I replace the Litespeed with an R3-SL, because it did this....

 

 

Good old Litespeed engineering, I returned it under warranty in July and stil have heard nothing, so it looks like their customer service is as good as their ability to design bike frames!

Allen.
 

 

 

Ouch,

Wow, that is a serious fracture! (now I've written that, is there an UNserious variety?)

I convinced my wife that Titanium was for life when I bought it - then had to eat my words 18months later when the drive side chain-stay fractured.  At the time, Litespeed Customer Service was VERY good as they explained the design change they did to cure this, repaired the bike and completely re-decaled it and even threw in a new Titanium seat post clamp - ALL done with a two week turnaround.

That was some 5 years ago now so times seem to have changed in the deep south of the USofA...  the kicker to all of this blurb is - the really nice Ti seatpost clamp they threw in, snapped in two this year!!!

I sure hope the titanium parts holding many aircraft together are better spec'd.

Ciao

PaulR

I've had a loose headset on my old mountain bike cause a wobble a few years ago.  That wobble wasn't nearly as bad as some I've seen, but it caused a fright.

I saw someone else hit an extremely bad speed wobble right in front of me in a race on saturday.  He got it again on the next decent, and immediately stopped.  Later I heard over the radio his Trek frame had cracked.  That wobble was really bad.

I've had a bad wobble on my Giant due to a bad Shimano front wheel.  It wasn't a classic speed wobble, as it depended more on the road surface and the steering angle than the speed.  Now I use that wheel on the indoor trainer only.

Check the headset first, because it's cheap and easy and common, but it could be anything.

In my limited experience wobbles are much more likely to happen around 50 kmh than 80 kmh.  At least those caused by mechanical problems.
 

Please correct me if I am mistaken... I have read in a few places that speed wobble is more frequent in the larger frame sizes due to the longer tube legnth. 

Brian

seven.62, I'm with greg66. I had a similar problem as you. On a descent, I reached 32-33 mph and the wobble started. I didnt know what it was and just waited to flip (assuming a bad headset). Waited some more, and still hadn't flipped so I slowly braked the bike, stopping in the middle of the road. After catching my breath I realized I had my first speed wobble. the headset was tight, no problem. I took the rest of the downhill at less than 30mph and finished the day okay. There is a section of downhill that I regularly take at 45mph, so i dont think my wobble was because of high speed necesarrily. But of course, i really dont know what caused it. I had never wobbled before or since. Yes, I am 6-5 riding a 61cm Soloist Team, but I've never heard of speed wobble occuring more often with large frames. EDIT: don't put a less than sign in your post, it will cut your reply short

It was a serious speed wobble on a Trek 5000 that "steered" me into the Cervelo fold.  Near the bottom of a moderate hill, divided highway, 64 kph.  Shimmey progressed to a violent speed wobble, and I was trapped between concrete barrier and 100 kph traffic.  Wobble finally stopped when I stopped, fortunately upright.  Nothing apparently wrong with frame, fork, or tires.  Loose headset comments above not withstanding, one shop suggested that it could be the headset was too tight.  That jibes with experience on motorcycles, where tight or "indexed" steering head bearings, and the steering inputs necessary to overcome them, can cause the motorcyle to wobble.  However, in the case of the Trek, I traced it to my attempts to convert a road bike into a tri bike.  I had reversed the seat post, and moved the seat as far forward as the seat rails would allow.  Two independent bike fitters, one of which who had put me in that seriously forward position, concluded that I had shifted too much weight on to the front end.  The angle of the hill, combined with the speed, and ultimately the application of the brakes, put too much weight ahead of the steering axis.  Didn't think to try clamping the top tube, and clenching the seat with my butt did no good at all.  Turned the Trek back into a road bike, and now ride a P2C since August.  Same forward riding position, if anything perhaps a half degree steeper seat tube angle, and no sign of instability.  By the way, I went with a largish (58cm) frame for my height (5'10), and it fits great.