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Old 12-06-10, 04:07 PM   #1
NickyBoy
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Brake Shudder Really That Bad?

I read a lot of threads about people trying to eliminate or minimize front brake shudder. Ever since I switched to a high profile canti my cross bike has been doing it vigorously.

Is it really that big of a deal or is this just a comfort issue? Is it going to cause damage over time? My headset is set up perfectly, the vibration doesn't bother me as long as I know it isn't going to cause me mechanical problems or a catastrophic crash.

its a voodoo wazoo, steel frame and fork.
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Old 12-06-10, 04:13 PM   #2
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A strong low frequency shudder as opposed to a squeal is bending all the parts over quite a cycle of travel. For the long term health of the metal as well as comfort to the rider I know that I'd want to correct it. Also the shudder is being reflected into the contact patch on the ground. I don't see how a strong shudder can do anything but hurt the maximum reachable friction coeffienct. So likely your maximum attainable braking rate is suffering as well.
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Old 12-06-10, 04:13 PM   #3
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I can't really determine if it's damaging or not, but it sure affects handling.
a brake booster plate can usually solve the problem.
I think my fork ends moved a good 1.5in when it was shuddering under braking.
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Old 12-06-10, 05:28 PM   #4
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No one can say how bad it is because they vary from simply annoying, to total loss of brake modulation and control. If it isn't affecting control, you may decide to live with it, or try to improve or eliminate it entirely.

One thing to consider is how it would affect braking in an emergency situation. Brake shudder that may be acceptable for normal conditions may not be acceptable in a hairy descent or emergency stop.

It's your call, but if it were me, I'd do whatever I could to have predictable braking that didn't affect control.
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Old 12-06-10, 05:38 PM   #5
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Brake shudder that may be acceptable for normal conditions may not be acceptable in a hairy descent or emergency stop.
You don't need to convince me.
I recently swapped out the Shimano pads for KoolStops on a bike with canti's.
Suddenly I found that on descents >= 9%, my front brake has no modulation at all; It goes from off to full-on.
Not acceptable at all descending Flagstaff Mt which has hairpin turns and grades up to 16%.
I've put Shimano pads on the front until I get a fork-crown hanger installed.
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Old 12-06-10, 05:47 PM   #6
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You don't need to convince me.
I recently swapped out the Shimano pads for KoolStops on a bike with canti's.
...
One of the perversities of front brake shudder is that changing the brake shoe to a higher friction compound to improve braking can make it so much worse. This is especially true when the primary cause is brake arm and post flex. The higher friction compound increases the ration of forward torque caused the rims motion to the compression force from applying the brakes. So at low braking force they shudder, and the only way to cure the shudder is to apply the brakes so hard you do an endo. Not a great choice.
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Old 12-06-10, 05:54 PM   #7
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I can only speak from experience with low-frequency shudder, and it is definitely a problem. During hard braking the front wheel can actually jerk back and forth so violently that it momentarily loses contact with the ground. And if you need hard braking you seldom have the time to release the levers and apply more gradually. It is a problem.
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Old 12-06-10, 06:43 PM   #8
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You don't need to convince me.
I recently swapped out the Shimano pads for KoolStops on a bike with canti's.
Suddenly I found that on descents >= 9%, my front brake has no modulation at all; It goes from off to full-on.
Not acceptable at all descending Flagstaff Mt which has hairpin turns and grades up to 16%.
I've put Shimano pads on the front until I get a fork-crown hanger installed.
even after toe in?
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Old 12-06-10, 06:55 PM   #9
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even after toe in?
Yes.
Adjusting the toe-in did nothing.
Bear in mind this is a *tall* frame.
When I built the bike, I only had to cut about 1cm off the steerer.
I suspect that long steerer is adding a lot of flex to the system.
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Old 12-06-10, 07:03 PM   #10
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Yes.
Adjusting the toe-in did nothing.
Bear in mind this is a *tall* frame.
When I built the bike, I only had to cut about 1cm off the steerer.
I suspect that long steerer is adding a lot of flex to the system.
I got it on a 16" mtb frame that uses a 1-1/4 threaded steerer tube fork.
I suspect the crown joint or the fork blades are not as beefy as the steerer, either that or the cable hanger is too weak on my bike.
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Old 12-06-10, 07:19 PM   #11
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This issue comes up frequently with bikes using cantilever brakes with the front brake cable housing stop located above the top race of the headset. Lennard Zinn posted a major article on this on the VeloNews web site a few months ago. His analysis was that flex in the steerer tube causes a pulsing in the brake cable that rapidly changes it's tension and, therefore the braking action.

The quickest fix was to mount a cable housing stop on the fork crown using the hole in the crown intended for a front fender or caliper brake. This, of course, only works if there is a suitable hole or you can drill one.

I don't know if his analysis is absolutely accurate but moving the cable stop to the fork crown has solved this problem for many who have tried it.
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Old 12-06-10, 07:31 PM   #12
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I presume this is the article?
http://velonews.competitor.com/2010/...o-cross_101807
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Old 12-06-10, 07:32 PM   #13
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This issue comes up frequently with bikes using cantilever brakes with the front brake cable housing stop located above the top race of the headset. Lennard Zinn posted a major article on this on the VeloNews web site a few months ago. His analysis was that flex in the steerer tube causes a pulsing in the brake cable that rapidly changes it's tension and, therefore the braking action.

The quickest fix was to mount a cable housing stop on the fork crown using the hole in the crown intended for a front fender or caliper brake. This, of course, only works if there is a suitable hole or you can drill one.

I don't know if his analysis is absolutely accurate but moving the cable stop to the fork crown has solved this problem for many who have tried it.
I would say it's quite correct.
as the fork flexes back and forth, the geometry of the fork changes, and that causes the cable to get taught and slack, which obviously causes the brakes to pulsate.
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Old 12-06-10, 10:09 PM   #14
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Also the shudder is being reflected into the contact patch on the ground.
Budget anti-lock : p
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Old 12-06-10, 10:23 PM   #15
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Originally Posted by Shimagnolo View Post
Yes.
Adjusting the toe-in did nothing.
Bear in mind this is a *tall* frame.
When I built the bike, I only had to cut about 1cm off the steerer.
I suspect that long steerer is adding a lot of flex to the system.
In my experience the distance from the cable hanger to straddle cable also matters. I'm a huge fan of fork mounted cable hangers for this and other reasons.
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