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Speed wobbles driving me crazy…..(10 posts)

Speed wobbles driving me crazy…..DY
Mar 23, 2002 5:44 PM
I'm about to take my bike into the LBS, but I wanted to see if anyone here had any experience/input on this situation. I have been experiencing speed wobbles (whole front end seems to shake back and forth) seems like a wet noodle at high speed downhills. It isn't too confidence inspiring as a matter of fact it is downright scary. On flats and everyday it handles fine. After some large hill climbing at about 30 mph + it starts to happen. I thought it was a crosswind, because it doesn’t always happen. It was windy today and it happened twice to me but it didn’t happen to my friend on a similar bike. He maxed out at 45 mph on the hill. So that made me think that it is not the wind. Today I experimented a bit trying to move my weight around, but I couldn’t notice much. It has me pretty baffled. I’d love to hear any comments.

Here are the details about me and my bike:

Me – 6’0”, 180 lbs. Inseam 80.5 cm

Bike - 55cm c-c. Top tube 56cm, 73.2 deg. seat and head tube.
1” alloy steerer 43 mm rake Columbus Carve carbon.
Campy Chrous threadless headset. Tight with no slop. 17.5mm of headset spacers.
Cinelli B-groove bars (44cm) 12 cm Cinelli Alter stem ( I know heavy, but I thought it kind of look interesting).
Campy Proton wheels, Continental Grand Prix 3000 23c 110 psi.

Am I leaving anything out? I think this should be enough details. The only weird thing may be my frame size. I am long waisted (torso) but relatively short legged for my height. For my inseam I should actually be riding something smaller, but I went for the next size up so I could get a longer top tube. I think the bike fit me well lengthwise. I have had it since about October.

One other thing....everything seems to functioning correctly otherwise. Parts are not loose, wheels are true, stem and bar tight, front wheel on tight, etc.

Thanks.
re: Speed wobbles driving me crazy…..mwood
Mar 23, 2002 6:23 PM
I had a weird speed wobble awhile back which was due to a tire which was not exactly "square to the world" i.e. it was a blem with a variance in the sidewall.
Frame tweakage may also result in dicy stability.
re: Speed wobbles driving me crazy…..the bird
Mar 23, 2002 6:31 PM
Get the same @#$%%% wobble on my 5200 at around 35 mph every blue moon!! I can get the same thing sprinting when I have a death grip on the drops. Try loosening yourself up. Holding the top tube between your knees after spinning out on a decent helps too!!
re: Speed wobbles driving me crazy…..Andor
Mar 24, 2002 8:46 AM
What the heck is a speed wobble, are you getting them because you have bad bike balance?
Exactly my point, one should not know what a speed wobble isDY
Mar 24, 2002 10:51 AM
One should not even know what a speed wobble is if their bike is set up right (at least that is my assumption) A speed wobble has nothing to do with balance, it has do do with your front end shaking back and forth at speed. Wobbling all around. maybe a tire is messed up of the headset or the fork.

Should I have a fork with less or more rake? Would that make difference or should mine be ok?

I'll keep digging deeper.
Big Picturegrzy
Mar 25, 2002 11:43 AM
The bike and rider together are a dynamic system. You as the rider have considerble influence in how the bike rides. To be sure there are many things about the bike (e.g. wheels) that have a large influence. That your buddy doesn't have the problem and all components seem fine you may want to consider swapping bikes with your buddy for some test rides. I'm williing to bet your technique has a role in the problem and it's pretty easy to determine. Getting tense on the bike and having a death grip on the bars is a sure way to get the wobbles on a frame with agressive geometry.
oscillation! my dear watson.retroger
Mar 24, 2002 11:37 AM
You my friend, have the same problem I have with my bike. The fork rake is (wrong?, who can say) At speed, with not too much weight shifted to the front, the wheel begins to oscillate. I have not corrected this problem on my bike because I can generally avoid it and the trade off is aggressive handling. The solution is a new fork. that is the only solution that will defiantly work. Perhaps you could go with a longer stem to put more weight out front but if the bike is fit well now, then that would seem like a silly thing to do. (I'm going to guess that your rake is less than 4.5)
Good luck.
Not uncommon, but not commonKerry Irons
Mar 24, 2002 7:58 PM
Speed wobble is a constant topic on bike discussio boards. Causes are as unique as the bike and rider. It can almost always be prevented by clamping the top tube between the knees. Common culprits are badly adjusted head sets, out of true or out of balance wheels, flexy frames, and flexy forks. But none of these guarantee speed wobble, nor does eliminating any of them guarantee the elimination of the wobble. Since there is nothing you can do about flexy frames and forks, your best bet is to check that your wheels are true and properly adjusted, likewise adjust your head set, and try a different set of tires. Speed wobble is essentially the excitation of a resonant frequency in the combination of frame and rider, so anything that changes the resonant frequency will work.
Agree with flexy frame/forkdzrider
Mar 25, 2002 5:26 AM
I had speed wobbles on my Vitus 992 - particularly on windy days. The best cure was to take my hands off the bars when I first felt the front end shake. Somehow the unloaded front end would right itself. Once I accepted this act of faith I never again got serious wobbles. A friend recommended pulling the front wheel off the ground, but I never tried it. Once the wobble got going it was scary enough to effect my enjoyment of downhill riding for weeks.
Agree with flexy frame/forkgrzy
Mar 25, 2002 11:39 AM
Yes, rider input is a big factor in speed wobbles. My bike can wobble if I'm tense - when it starts to wobble it's just a remindedr that I need to relax a bit. People are quick to look for an equipment cause when often it's the rider.