Fork trembles under heavy braking
11-21-08, 10:28 AM
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Fork trembles under heavy braking
I bought a used Gunnar crosshairs recently. The parts on this bike are really nice for what I'm used to on a road bike.
In particular the brakes are really powerful, and I've noticed that the Fork can sometimes wobble and tremble under heavy braking. If I'm careful and I observe the Fork during hard braking, it sometimes looks like its giving and shuddering backwards under the strain.
I hope this description of the symptom is accurate enough. Is this an issue of brake pad toe or is it possible that this Fork has been fatigued too much?
In particular the brakes are really powerful, and I've noticed that the Fork can sometimes wobble and tremble under heavy braking. If I'm careful and I observe the Fork during hard braking, it sometimes looks like its giving and shuddering backwards under the strain.
I hope this description of the symptom is accurate enough. Is this an issue of brake pad toe or is it possible that this Fork has been fatigued too much?
11-21-08, 10:31 AM
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I bought a used Gunnar crosshairs recently. The parts on this bike are really nice for what I'm used to on a road bike.
In particular the brakes are really powerful, and I've noticed that the Fork can sometimes wobble and tremble under heavy braking. If I'm careful and I observe the Fork during hard braking, it sometimes looks like its giving and shuddering backwards under the strain.
I hope this description of the symptom is accurate enough. Is this an issue of brake pad toe or is it possible that this Fork has been fatigued too much?
In particular the brakes are really powerful, and I've noticed that the Fork can sometimes wobble and tremble under heavy braking. If I'm careful and I observe the Fork during hard braking, it sometimes looks like its giving and shuddering backwards under the strain.
I hope this description of the symptom is accurate enough. Is this an issue of brake pad toe or is it possible that this Fork has been fatigued too much?
11-21-08, 11:04 AM
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Yeah its definitely not the headset.
Think this would go away if i put the stiffest 1" Fork I could find in there?
Think this would go away if i put the stiffest 1" Fork I could find in there?
11-21-08, 11:06 AM
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I've experienced this on pure road bikes. I figured it was just sticky brake pads or something.
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11-21-08, 11:14 AM
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Try "toeing" in your front brake pads. The rear of the pad should make contact with the rim before the front does. The pad wont grab as much this way. This is very common on canti brakes, and is usually more pronounced at slower speeds.
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11-21-08, 11:29 AM
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+1 for the toe in on brake pads. also reduces brake squeal in the rain.
except the front of the pad is supposed to hit the rim before the rear.
easiest way to do it, adjust your pads so that they hit the rim flat, loosen the bolt enough to wiggle the pad, insert credit card at the rear edge and tighten the bolt down. if done correctly you should now have ~1mm of clearance at the front and 2~3mm of clearance at the rear of the pad.
except the front of the pad is supposed to hit the rim before the rear.
easiest way to do it, adjust your pads so that they hit the rim flat, loosen the bolt enough to wiggle the pad, insert credit card at the rear edge and tighten the bolt down. if done correctly you should now have ~1mm of clearance at the front and 2~3mm of clearance at the rear of the pad.
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Last edited by AEO; 11-21-08 at 11:33 AM.
11-21-08, 11:51 AM
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except the front of the pad is supposed to hit the rim before the rear.
. Here's the Park Tool "How To"
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11-21-08, 01:10 PM
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The fork is not stiff enough. Assuming we've ruled out incorrect brake adjustment and headset adjustment.
11-21-08, 01:24 PM
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This is cross bike with cantilever brakes. Fork shudder is very common with the canti's, and in some cases almost impossible to eliminate completely. You could be right, but I'd say it way more likely an issue of toeing in the pads and/or changing the pad/rim combination.
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11-21-08, 02:44 PM
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Also, the longer you ride the bike, you get to really know when and how it's prone to do it.. and you learn to "modulate" your braking around that point.
As speed comes down under braking power, you reach the resonant frequency and it starts to shudder.
If you momentarily and gently let off and reapply the front brake, the shudder will have stopped, and you will then be going slower than the resonant frequency, and the shudder will usually not recur.
My cross bike shudders... but I got used to it and now just modulate the brakes around the shudder without really thinking about it.
As speed comes down under braking power, you reach the resonant frequency and it starts to shudder.
If you momentarily and gently let off and reapply the front brake, the shudder will have stopped, and you will then be going slower than the resonant frequency, and the shudder will usually not recur.
My cross bike shudders... but I got used to it and now just modulate the brakes around the shudder without really thinking about it.
Last edited by nycphotography; 11-21-08 at 02:48 PM.
11-21-08, 03:50 PM
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I also just realized that the fork is going to have the spots to bolt the brakes on so I wouldn't be able to buy just any fork without changing the brakes too. I'll learn to live with it
