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Frame Fork Vibration(8 posts)

Frame Fork Vibrationmtbmike
Sep 16, 2002 4:29 PM
Recently purchased Colnago CT1 with Force Carbon Fork.
Situation: At 25-30 mph. there is a vibration that seems to come from the front end. I am 185# and by all figures, the frame should be fine. ( it all checks out straight) Can anyone tell me if the Force fork is possibly too stiff or too soft? Any other ideas??? Help. Other stuff: There is visible deflection in the fork/ front end when I hit small bumps.
Speed wobbleKerry
Sep 16, 2002 5:01 PM
When you say vibration, do you mean you can feel a buzz through the handlebars, or do you mean the front end of the bike is oscilating like it was going to come apart. If the latter, you have the all to common speed wobble. It is the bike/rider hitting a harmonic resonance. Change the resonance as follows (several ideas): adjust the head set, change tires, adjust wheel bearings, clamp the top tube between your knees, pedal, stop pedaling, stand up, sit back down, tightly grab the bars, loosely grab the bars. End of the day, the head tube is too flexy, but there is nothing you can do about that. Of the 5 frames I've owned (all around 59-61 cm), the only one that did this was my 29 lb. Schwinn Sierra 15 speed (1964).
Speed wobblemtbmike
Sep 16, 2002 10:04 PM
Kerry,
It isn't as drastic as the front end coming apart. It is more like riding over a washboard, or rumble strips. It does seem harmonic in nature, as it happens whether descending or on flats. Enough of a vibration to make the cables shake. My first thought was the rear wheel but it checked out OK. It is actually that hard to determine where it is coming from. Seat or stays don't feel it. The fork doesn't really show it (visibly) Off the bike, I notice what seems to be a lot of torsional flex in the carbon steerer tube. I.E. when you grab the bars standing at the front of the bike and twist down with your wrists, or grab the front wheel between your knees and twist the handlebers side to side.wheel dances side to side over small bumps as well. Maybe the tubulars/wheel combo.? Ksyrium ssc/ conti. sprinter. Thanks for reply.
re: Frame Fork VibrationSilas_Greenback
Sep 16, 2002 5:13 PM
Before you go nuts making some or all of the changes mentioned above, check that the bolts that attach your stem to the fork are tight. I thought my new frame had this problem, and it was just the two bolts. If your steerer is carbon, be very delicate as you tighten.
re: Frame Fork Vibrationmtbmike
Sep 16, 2002 10:08 PM
Silas G.
Thanks for the reply. I will double check the bolts. Yes, it is carbon, and I have fears of crushing the steerer. I don't know if I am sold that carbon is a great material for steerer tubes. It seems too subject to failure in such a stress load area, as well as flexy.
re: Frame Fork VibrationSpunout
Sep 17, 2002 3:46 AM
About the flex in the fork, that is the fork doing its job at absorbing road shock. I remember my old Colnago with SL forks, they would flex 1" back and forth. Made for a velvety ride!

About the STAR fork, maybe your LBS would let you borrow another fork, go for a ride, and see if it is any better. Definitely a harmonic thing, with all of that carbon.
Sounds like a misadjusted/aligned headset.SnowBlind
Sep 17, 2002 6:59 AM
Have a good mechanic check it out.
I had some seating problems with the record headset, took a few reseating to get it to settle down.
Does it have a "notching" effect as well? If the spacers are not properly "faced" with the stem and the headset it can cause this problem as well.
BTW, at 235, let me tell you, carbon steerers are just fine.
Sounds like a misadjusted/aligned headset.mtbmike
Sep 18, 2002 6:24 PM
Yup, you nailed it. Messed with the headset yesterday and found the problem.