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wheel vibration(8 posts)

wheel vibrationdoug m
Mar 22, 2001 8:06 PM
I am not a racer but thought you would have the greatest knowledge on this subject. If I take my hands off the bars at speed the front of the bike vibrates. The vibration is more pronounced as the speed increases. I know the short answer: "Don't ride without your hands on the bars!" but I am trying to solve the underlying problem. I have a mongoose rx10.9 ti frame with a profile brc 1" threadless fork, not cut,spacers, ritchey pro threadless stem, fsa orbit uf headset, with ball bearing upper and roller bearing lower, spinergy spox wheels with the carbon hubs 1999 model, cheapo tubes and continental gp3000 tires. The wheels appear to be balanced. If you take off the tires and tubes and spin the wheel on the bike it does not appear to stop at the same postion every time If you add the tire and the tube, the wheel does stop at the same point every time. The lowest point is always where the valve stem is so I assume that is the heaviest point. If that is the whole problem I need to know a tube that has the lightest presta valve (short valve stem would be fine as the '99 spox were not aero wheels). but I am concerned that even with that the wheel will still be unbalanced. I am also afraid that because of the low rotational mass of the spox (most of the weight toward the center) that this magnifies the lack of balance at the rim. I also don't know if it is a problem with the profile brc fork (vibration or not stiff enough)or the fact that overall the weight of the front of the bike is just so light that any unblance causes this. I had an old (mid '80s)trek that was a beater with prebuilt wheels and never had this problem. Thank you for reading this and I do appreciate any help you can give. Doug
re: wheel vibration... some thoughts.Old Guy
Mar 23, 2001 7:32 AM
A couple thoughts:

1. You're assuming it's the front of the bike that's causing the vibration. I would check the alignment of your rear wheel. You'll need a measuring tape to make sure the distance from your chain stays to the rim are identical. Adjust the dropout screws accordingly.

2. Are your hubs adjusted? Is there ANY play in them? Repack them just to make sure. Check the races. It doesn't take long.

3. Is your headset in adjustment? OK, if it is, check those races again to make sure there's no pitting or irregularities.

-Old guy

ps: After years of road racing motorcyles, I learned that a lot of front end problems actually come from the rear. I have found this to be occasionally true for bicycles as well, ergo my pt. #1.
re: wheel vibration... some thoughts.doug m
Mar 23, 2001 1:45 PM
Thank you for the ideas. The bike was set up by my lbs but I will have them check it out Thanks again.
Check headset tightness first ...Breck
Mar 24, 2001 6:17 AM
Check the headset for excessive play first, then the front wheel bearing adjustment, lastly the front tire. Hopefully one of these is the culprit, otherwise ??? Let us know when you solve the problem.

I have an OCLV road and a Klein MTB with the Chris King threaded headset which have never loosened up but the specialized steel road Allez Pro came with a standard brand which is stubborn to remain adjusted and has caused this front end vibration in the down hill 40-45 mph range that you refer to and it's alum noodle fork makes it worse I am convinced. These are all quills and have never adjusted the Ahead-set style you mention but am led to believe it may be a bit tricky to the uninitiated. Am sure any probs you find your LBS will take care of.

To check head set tightness straddle the bike, feet flat on the ground; firmly apply max pressure to the brake levers so as to tightly clamp the wheels. Rock the bike back and forth. There should be no head set looseness. If there is adjust the head set accordingly. The rule of thumb is that when you raise the front end and turn the stem from side to side there should be no binding; looseness or "scratchy" feeling, etc.

If the headset is OK, check the front axle/ bearings for looseness. Release the QR, make sure the front wheel is in the neutral position re-clamp tightly. Hold the bike steady by the front handle bar/ stem with one hand and with the other grasp the top of the wheel and try and rock back and forth. There should be no play here. If there is then the front axle nuts will need to be tightened by the LBS ( or get a good bike manual & tools and try this your self ).

Lastly if none of the above, then the front tire may be faulty, out of round, etc. which may only show up at speed. Spin the front wheel and visually see if the tire spins with the circumference not bobbing up and down, side to side, etc. excessively. This is relatively rare but can happen.

Am out of ideas .... but believe the problem lies with front end looseness in either the head set or the axle. Good luck and let us know the solution.

cheers
bgcc
Check headset tightness first ...doug m
Mar 25, 2001 4:28 PM
Wade thank you for the information I will have my lbs see what they can do.
re: wheel vibrationKerry Irons
Mar 24, 2001 2:27 PM
The vibration of bicycle frames is a highly complicated event. In physical terms, your bike has a resonant frequency that is stimulated when you reach a certain speed. This is not uncommon. Without any hard data, I would guess that something between 10 and 25% of road bikes have this problem. Many riders never know they have it because it occurs at very high speeds or because they don't go no-handed at these speeds. There are lots of arguments about frame stiffness, the relationship between frame dimensions, forks, headset adjustment, wheel weight, bearing adjustment, etc. Some frames will never do this regardless of rider weight, wheel weight, adjustment, etc. Some will do it regardless of these factors, and some will do it only when a certain (unpredictable) combination of factors are in play.

Headset adjustment is often pointed to as a solution, because changing HS adjustment changes the "stiffness" between the frame and fork/wheel. A headset with fretted (dented) races should be changed, so if you have "index steering" you should eliminate it - this will allow the fork/wheel to move smoothly and therefore change the effective center of mass of the system. The weight doesn't move but if the wheel and fork have a different relation in space to the frame, this will shift the resonant frequency. Often changing tires or wheels also eliminates or triggers it. Within the range of things you can change easily, look hard at the headset, hold on to the handlebars and/or clamp your knees to the top tube when descending (changes the center of mass of the frame/fork). You may have to accept that your bike vibrates, and just deal with it.
re: wheel vibrationdoug m
Mar 25, 2001 4:26 PM
Kelly thank you for the information. The parts are all new Doug
re: wheel vibrationdoug m
Apr 15, 2001 8:57 AM
My lbs tighted the headset 1/2 turn and it fixed the problem. thank you to all Doug