My Cervelo P2 has recently started exhibiting a wobbling behavior. I first noticed this a Oceanside, coming down the 25mph speed limited descent. At the time I was riding my Hed Jet 9s andattributed it to the crosswinds. I had no problem of the sorts on the descents last year, even at higher speeds where the speed was not limited. However, it happened again yesterday, coming down an 11% grade, on my training wheels (the OEM Shimano R500), and no noticeable crosswinds. This is really scary.
Does anyone have a good explanation for this? Given that it’s been two different sets of wheels and crosswind and no crosswind when it has happened. My fit (saddle and aerobar position) has been the same on the same descent at Oceanside with the same wheels. I’m guessing it’s in the frame and maybe the headset. The only changes in the bike has been move from a Profile Design Aerodrink to an X-Lab Torpedo mount and bottle and a switch from a bento box to a toptube mounted gel flask. It was also brand new when I rode it at Oceanside last year. Now it’s a little over a year old has been ridden quite a bit. I’m bringing it to the ship today to have it checked out. I’m riding Wildflower Long Course and most definitely do not want this happening (there or anywhere else). Does anyone have any ideas about causes and solutions?
90% chance it is either a headset or front hub that is not adjusted properly.
90% chance it is either a headset or front hub that is not adjusted properly.
Donkeycrap.
http://forum.slowtwitch.com/gforum.cgi?post=2435409#2435409
Read the link at Sheldon Brown’s (RIP) web site that talks about shimmy.
My Cervelo P2 has recently started exhibiting a wobbling behavior.
The Sheldon Brown suggestion is good, but it assumes that you have always had wobble with the setup. In your case, if I understand your post, is that you did not have wobble under these conditions before, but suddenly do now. If that is true:
You have changed something to induce the wobble that Sheldon is discussing, and fixing it is a matter of figuring out what that is and undoing it.
It could be as simple as your headset, your position, a worn tire, etc.
It could be as complicated as something is bent or cracked because the bike fell over at a race, got banged in the garage, hit a pot hole, etc.
It also could be that you have changed your riding style for some reason. You changed the set up slightly and now you are more upright, or you are more aero but uncomfortable and are gripping the bars tighter.
In other words, it could be anything.
I got wobble for the first time on my bike a few weeks ago while doing a very steep technical descent (40+ mph) due to hitting a crack in the road at just the right angle. It took a lot of mental control to NOT hit the brakes and set up, both of which would have be paramount to suicide. For the rest of the descent I was expecting/fearing more wobble, and actually got wobble a few times. Once I realized that I needed to relax and start racing again I had no more problems. The moral? Wobble can be induced by a shaky rider, also.
Sheldon first presumes that your bicycle is properly adjusted…if all is adjusted (headset, hubs) then refer to Sheldons article.
Sheldon first presumes that your bicycle is properly adjusted…if all is adjusted (headset, hubs) then refer to Sheldons article.
Except that you are wrong. From the article:
“Shimmy is not related to frame alignment or loose bearings, as is often claimed. Shimmy results from dynamics of front wheel rotation, mass of the handlebars, elasticity of the frame, and where the rider contacts the bicycle. Both perfectly aligned bicycles and ones with wheels out of plane to one another shimmy nearly equally well. It is as likely with properly adjusted bearings as loose ones. The idea that shimmy is caused by loose head bearings or frame misalignment seems to have established currency by repetition, although there is no evidence to link these defects with shimmy.”
Just Old Again has it correct. I had this same problem with my last bike. If I remember correctly, there was nothing I could do mechanically to the bike to stop it. Whenever it occurred, I would shift my weight back and raise my butt off the seat slightly. That seemed to stop the vibration. Another solution I’d read was to shift weight back, raise up off the seat and pinch the bar with your knees. No way I could do all that at the same time! Or maybe it was; shift weight, raise butt, grip bar with knees and curl the right side of you lip down while breathing out, can’t remember.
Sheldon first presumes that your bicycle is properly adjusted…if all is adjusted (headset, hubs) then refer to Sheldons article.
Except that you are wrong. From the article:
“Shimmy is not related to frame alignment or loose bearings, as is often claimed. Shimmy results from dynamics of front wheel rotation, mass of the handlebars, elasticity of the frame, and where the rider contacts the bicycle. Both perfectly aligned bicycles and ones with wheels out of plane to one another shimmy nearly equally well. It is as likely with properly adjusted bearings as loose ones. The idea that shimmy is caused by loose head bearings or frame misalignment seems to have established currency by repetition, although there is no evidence to link these defects with shimmy.”
Actually I am not wrong, you are reading it out of context. Like I said, if it has always wobbled then Sheldon is correct. If it suddenly starts, then something has changed, and you need to figure that out. The part that you have bolded only supports that. A tight bearing might wobble, it might not, and if it didn’t wobble it might when it loosens up, then again it might not. Same with the frame. A straight frame might wobble, a bent one might not. Bend a frame and it might wobble, and it might stop wobbling.
I invite either of you to make your headset about 1.5mm loose, or just a tad on your front hub…just enough to feel some motion…then shoot down a mountain pass - I already know the result.
As for getting rid of a shimmy, your instructions are correct.
Two years ago I had an ST approved bike (super fast aero one). It got a shimmy at 33-35mph every time…bad shimmy. Changed wheels, forks, bars and on and on - could reproduce like clockwork. I gave the bike away.
Sheldon first presumes that your bicycle is properly adjusted…if all is adjusted (headset, hubs) then refer to Sheldons article.
Except that you are wrong. From the article:
“Shimmy is not related to frame alignment or loose bearings, as is often claimed. Shimmy results from dynamics of front wheel rotation, mass of the handlebars, elasticity of the frame, and where the rider contacts the bicycle. Both perfectly aligned bicycles and ones with wheels out of plane to one another shimmy nearly equally well. It is as likely with properly adjusted bearings as loose ones. The idea that shimmy is caused by loose head bearings or frame misalignment seems to have established currency by repetition, although there is no evidence to link these defects with shimmy.”
Actually I am not wrong, you are reading it out of context. Like I said, if it has always wobbled then Sheldon is correct. If it suddenly starts, then something has changed, and you need to figure that out. The part that you have bolded only supports that. A tight bearing might wobble, it might not, and if it didn’t wobble it might when it loosens up, then again it might not. Same with the frame. A straight frame might wobble, a bent one might not. Bend a frame and it might wobble, and it might stop wobbling.
I wasn’t replying to you, so I wasn’t saying that this contradicted what you said. Unless you are really R10C…
Did it shimmy from the time it was new or develop the shimmy later on?
Two years ago I had an ST approved bike (super fast aero one). It got a shimmy at 33-35mph every time…bad shimmy. Changed wheels, forks, bars and on and on - could reproduce like clockwork. I gave the bike away.
Jeez, Chip, why didn’t you just adjust the headset or front hub? I’ve heard that 90% of the cases of speed wobble are caused by that.
That bike fell into the 10%.
You really should get a real world education before you start to quote Mr. Brown and claim his stuff is gosphel…it is really good…but, some time as a wrench and maybe even more time at say…United or Barnetts Bicycle Institute could give you some more real world knowledge. To think that a headset or hub CANT cause a shimmy is just ignorant. I again invite you to prove this wrong by making yours on your personal ride loose.
(Oh, yes I did graduate from BOTH United and Barnetts). If I recall, when I was certified by Wheelsmith they also touched on the HS and Hub for being culprit for some shaking…odd how that would work - a loose rotating part causing a shimmy…damn physics.
That bike fell into the 10%.
You really should get a real world education before you start to quote Mr. Brown and claim his stuff is gosphel…it is really good…but, some time as a wrench and maybe even more time at say…United or Barnetts Bicycle Institute could give you some more real world knowledge.
Had you actually read and comprehended the article on Sheldon’s web site, you’d realize that none of those words were Sheldon’s: it’s the entire wreck.bikes FAQ entry on shimmy, as written by Jobst Brandt. Who, by the way, has probably forgotten (if he ever forgets anything) more about wrenching than you or I’ve ever learned.
My QR wobbled like crazy. I tried everything I cold think of: New wheels, changed the bars, I even put the computer on the opposite side, nothing helped. I was at the point of either trashing the frame or living with the wobble until I brought it the wrench.
He tried to tighten the headset but even at it’s tightest it was still not tight enough for him. He cut the fork a fraction shorter and then tightend the headset, no more wobble/shimmy.
CS
Ditch the X-lab.
Ron W.
Thinking about it, since it’s a change from the non-wobble configuration. However, I’m not sure it makes any difference versus a the Aerodrink.
This happened to me recently in a road race. It was my first race with 808s. I was sitting middle pack going down a steep hill and we were probably approaching 40mph when the wobble started. It really freaked me out. Another rider told me the put my knee against my top tube, which eliminated the problem. As for the cause, Im not sure. Good luck.