Singlespeed & Fixed Gear - speed wobbles -- what's wrong?

i have noticed recently that i get a lot of wobble in my front end when i'm going really fast in longer flats and down hills. this is definitely worse when my hands are close to my stem and is still considerable when i'm further out on the bullhorns or out on the ends.

my wheels are true and i don't see any other problems - what could be wrong? headset? fork? hubs? something bent i can't see? something installed wrong?

i have only noticed this recently and haven't had any wrecks or anything. i ride a KHS aero with the following changes from stock:

- nitto track stem
- nitto bullhorns
- campy headset (i'm not sure which model, it was on there when i bought it... it has a black rubber ring on the bottom and top cups)
- EAI cog in back
- shimano rx100 road cranks
... wheels are stock hubs/stock araya rims.

any insight as of what to check out and how to do it if its a DIY job would be totally appreciated. gracias.

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

interesting... i'll pay more attention to what i'm doing more tomorrow, but i'm definitely riding with my hands on the bars. it definitely had me concerned that the fork was bent or some ****

I love Sheldon Brown.

It used to happen to me during fast downhills no handed on a particular bike. I gradually realized that it was related to weight distribution. Obviously make sure all is kosher in your front end. headset bearings/adjustment, wheel true, but then look at things like seat position, and stem length. if your seat is way back, and your stem is high, short or both, you might improve the situation by shifting the weight distribution more towards the front wheel. i.e. lengthen the stem, or lower the bars. then adjut the seat a correspending amount forward to amke up for the different stem length.

BTW, Sheldon Brown was a postin' recently on the 'What is a Retrogrouch?' thread on the General Forums. How cool is that? Check it out!(Sorry CEYA, the Jedi Council has decided that you are far to young to lead the Jedi. Due to Master Shel-Wan's recent reappearance, we must ask you to step down....)

Don - good chime in.
Sheldon isn't the end-all, be-all.

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

http://images.amazon.com/images/P/B00005NG3H.01.MZZZZZZZ.jpg

i knew you didn't appreciate my powers!

there is the dark side young jedi knight. i am now..




LORD CEYA!

thats not sheldon, its jobst brandt

"Jobst Brandt is a mechanical engineer (Stanford) with extensive experience, having worked for Porsche automobiles, Stanford Linear Accelerator Center, Hewlett-Packard and Avocet bicycle products.

He is best known in the bike industry as the author of The Bicycle Wheel , the definitive text on the theory and practice of building spoked bicycle wheels"

thanks dw... i could attribute it to my old ass set of tires, although i don't skid to often and don't run a significant skid patch. new ones are coming next week so i can see if that's the issue.

if it is a fork issue, how can i test/check alignment to know for sure?

']Don - good chime in.
Sheldon isn't the end-all, be-all.

Stormtroopers,please escort this man to my chambers for questioning....

...and find this 'Lord' Ceya, and his apprentice, [165]...if you have to search the entire galaxy...I want them alive!

i feel that sheldon's article is wrong when it comes to speed wobble. i had a wobble in my road bike, that wouldn't go away, even when doing the knee-toptube, etc, that people say you're supposed to do, because "speed wobble is natural". You dont see anyone in the tour wobbling on the descents. sorry if i sound a bit grumpy on this subject, but crashing at 50mph and having probably 2 sq ft of road rash evenly spread over one's body isn't exactly the most fun of times, especially when they have to scrape the dirt out with nail files and such in the ER.

Upon scrutiny of my bike at the shop i had bought it at, we determined the frame appeared to be perfectly aligned, so it had to be the fork (common amongst speed wobble cases, esp with a carbon fork). after dealing with raleigh's warranty dept all summer, i finally got a replacement fork in august, and ever since replacing it, no more wobbles. after looking at my old fork, you could tell the fork blades seemed to be somewhat off kilter. the front wheel would never line up right away either, you would have to play with it to get it to sit perfectly in the middle, where you should just be able to slide it all the way up on the dropouts and forget about it.

theres my 2cents on the subject

thanks dw... i could attribute it to my old ass set of tires, although i don't skid to often and don't run a significant skid patch. new ones are coming next week so i can see if that's the issue.

if it is a fork issue, how can i test/check alignment to know for sure?


Park makes a fork alignment checker, as do others. Ask your LBS if they've got one. Frame checking is easier and can be done with a piece of string. I don't know of any good short-cuts for fork checking.