Speed wobbles

[Audible Anarchy]

I've sent the bike in for them to double check the headset - i have a feeling it might be the bearings too... as for getting more weight to the front of the bike, im hoping the longer stem should sort that out.

 

Lets hope the can get to sorted out before D2D on sunday - i can't imagine speed wobbling ilke that in a bunch - ppl will get seriously hurt. i should have it back this afternoon - and if it feels dodgy , screw that il ride my old alu bike and start shopping for a new frame.

 

so odd how it messes with your head tho! like, riding on tenterhooks the whole time " jo ,when is it gonna try chuck me off".

 

thanks for all the help guys, i hope it gets sorted.

Edited September 2, 2011 by Audible Anarchy

[Reg Lizard]

I've heard of sludge that hardened in a tube that caused a speed wobble.

[David Marshall]

Me again - I very much doubt headset wear is the cause, unless it is loose. The fact that you have only had three wobbles in 7000 km makes me think it is more likely to be rider related. You say it happens on Dainfern hill. Are you descending early in the morning? Could you be tensing with the cold? Has it happened on the way home when you have warmed up? I put my aluminium frame into a wobble at the start of last years D2D, in the neutral section on the N14. Shivering. Another guy in VC had the same problem further along the same section. I also did it during the Macsteel, just after the start when you go under the highway - dark glasses, no lights - cold rider tenses - bike wobbles. I used to be so bad down Dainfern that even today I sit at the back of the bunch in winter- just in case. NB braking worsens the wobble.

 

The fact is that changing anything that inhibits the wave will solve the problem leads to all the solutions - changing stem, wheels, fork etc. As I said before, unless there is an obvious problem you are unlikely to find what the real cause is.

[Shebeen]

This topic has been commented on here on the hub - I think under "shimmy" or "high speed shimmy". It is caused buy a wave like resonance developing in the bike similar to a wheel wobble in a car with an unbalanced wheel. Can have a host of causes - from rider tension to wheels to fork alignment and everything in between. Once you have eliminated any obvious damage as a cause you are reduced to resting a leg on the top tube or gripping the tube with your knees. My solution was to change my frame. I could control my bike but could not get up the confidence to really let loose on the descents. I suspect that my build (long legs, short trunk) was not compatible with the very compact frame I had. The distance from BB to top tube was short relative to the top tube to saddle measurement. My new frame is less compact and I have had no hassles.

 

just do a hubsearch under 'shimmy' and you'll find a few threads.

 

or just consult the oracle:

http://sheldonbrown.com/brandt/shimmy.html

[FlatCruiser]

I had the same problem earlier this year and i know how it messes with your head ! I changed my headset and my mindset My wobble always happened on the same decesent and the same place, same speed +-60km/h. The more i rode there the more tense i would get, you have to learn to relax, it's difficult to do but solves the problem.

[Audible Anarchy]

its happened in winter and late summer in the afternoon heat. its odd, cos i bomb that hill every week with the club usually without issues.

 

the one time it happened when a truck drove past.. could side wind be a cause? its normally pretty breezy down the bottom of that dip too? i ride relatively flat rims 23 mm. but they do have bladed spokes. however with that in mind , its happened with my beater wheels with normal spokes too.

 

i come from a background riding DH so i like to think i can handle decents pretty well? but yeah i can see how tensing shoulders etc... could trigger it.

 

i think playing with the setup may be the solution - i.e. the longer stem and possibly moving the saddle a little forward too. just to move the center of gravity slightly. its def nothing mechanical - as I've just had it checked out, reassembled the headset / fork etc...

[Audible Anarchy]

Update -

 

moved the seat a little forward to compensate for the longer stem . Boom - 84km /h and solid as a rock - seems it was my position on the bike (i.e. not enough weight forward).

 

thanks for all the help guys - so relieved its sorted now!