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Recreational Cyclocross and Gravelbiking This has to be the most physically intense sport ever invented. It's high speed bicycle racing on a short off road course or riding the off pavement rides on gravel like :The Dirty Kanza". We also have a dedicated Racing forum for the Cyclocross Hard Core Racers.

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Old 10-28-05, 04:14 PM   #1
ccharles
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Front brake chatter

When I brake hard, my front fork sometimes vibrates. I think the front brakes are grabbing the rim hard, then losing contact, and doing this in an oscillatory manner which leads to the chatter on my front fork. Has anyone else experienced this? Is it because my brakes (shimano cantilevers pairs with 105 levers) are set up improperly? Does anyone have any insight on how I can eliminate or minimize this behaviour? The bike is a 2005 Bianchi Axis if that is relevant.
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Old 10-28-05, 06:11 PM   #2
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Quote:
Originally Posted by ccharles
When I brake hard, my front fork sometimes vibrates. I think the front brakes are grabbing the rim hard, then losing contact, and doing this in an oscillatory manner which leads to the chatter on my front fork. Has anyone else experienced this? Is it because my brakes (shimano cantilevers pairs with 105 levers) are set up improperly? Does anyone have any insight on how I can eliminate or minimize this behaviour? The bike is a 2005 Bianchi Axis if that is relevant.
i had/have this on my Gios (road bike mid 90's). The frame has done many kilometres and there is some wear in the steerer tube which makes it impossible for me to tighten the threaded headset completely. The entire fork shakes under braking, which is problematic in the wet...

I recently built up an il Pompino (threadless headset) and used the front wheel from my Gios to complete the build while I get enough money to build a new front wheel. Guess what. Front wheel/fork shakes under braking - which suggests that while there may be an issue with the headset on the Gios, it is more likely to be an irregularly worn braking surface on the rim (in my case). I notice that the problem is more serious under wet conditions.

The front rim has probably done about 30,000km and has wear to match (Mavic SUP). I believe that I will fix the problem when i rebuild the wheel with a new rim. I don't know if this helps you, but I get paid on Friday so I should be able to give an update Monday week!


cheers


Marty
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Old 10-30-05, 08:01 PM   #3
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Quote:
Originally Posted by ccharles
When I brake hard, my front fork sometimes vibrates. I think the front brakes are grabbing the rim hard, then losing contact, and doing this in an oscillatory manner which leads to the chatter on my front fork. Has anyone else experienced this? Is it because my brakes (shimano cantilevers pairs with 105 levers) are set up improperly? Does anyone have any insight on how I can eliminate or minimize this behaviour? The bike is a 2005 Bianchi Axis if that is relevant.

I had the same problem with some old Shimano cantis (SLRs with shorter, fatter pads). These models are very sensitive to toe-in and need quite a bit of it. The ends of the pads that are toward the front of the bike need to be much closer to the rim. In other words, the pads will make a slight "V", pointing towards the front. This pretty much cleared up the problem. Also, make sure the pads are not hitting too high or low on the rim. It can take a lot of futzing to get canti pads lined up properly.
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Old 10-31-05, 12:09 PM   #4
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Almost all cyclocross bikes have this problem to varying degrees-it is related to head tube angle, at least partly. My bike chattered so badly when I first built it up, that I thought I was going to break the fork. It nearly drove me crazy. Eventually, I got rid of the chatter altogether. Here's are the things that I tried that helped:

1) Old MTB canties-I am using diacompe 987s-way better than the techtros I originally built it with-less play in the arms.
2) Good pads: I use kool stop salmons with no toe in.

3)finally, and this makes the most difference-a fork mounted cable stop-ditch the steerer tube mounted one, they seem to excite the oscillation.

Alternately, you can run V brakes with a travel agent-that works too, but I prefer the cantilevers myself.
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Old 10-31-05, 03:49 PM   #5
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I've had the same problem. I hadn't thought of the idea that the headtube angle had something to do with it. But I'm guessing I have a similar headtube angle to a lot of CX bikes with my bike, which has a touring frame.

I'm convinced it's usually a combination of having your headset bearings loose and having your rim be worn unevenly. Uneven rim wear (or small dents in the rim) probably makes it more likely for your headset to loosen up, and having a loose headset makes it more likely for your rim to wear unevenly.

What I would suggest you do, if you can, is replace your headset bearings and your front rim. If you have serviceable headset bearings, not a cartridge, you should also consider either replacing the bearing cups or taking them out and putting them back in, in a position rotated 90 degrees from where theys started. (put a mark on them so you can tell). Doing that will place the badly-worn parts of the bearing cups in a position where they won't be in the positions that take the most stress. you can remove your bearing cups using a flat-head screwdriver and a hammer (get the bearing cup partway out on one side and then switch sides as often as is necessary). When you put the bearing cups back in, they'll settle in to position and the bearings will loosen some, so re-tighten them promptly or your brake problems will return.

The advice to use stiff brake arms is also very worthwhile. Another small factor could be wheels being out of true/out of round.
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Old 10-31-05, 04:42 PM   #6
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I used to be bordered with chatter, but not anymore.
What was the solution for me was a good headset that doesn't loosen up all the time.
It seems to me that a standard 36/45º alu cup design like Ritchey and Cane Creek just don’t do it.
If you're able to mount a fork mounted cable stop like Darkmother's mention, I think that's a very good idea too.
If the headset loosens, when if it's a Ritchey, Cane Creek or any other standard 45º cartridge type,
the fork wobbeling wont interfere with the brake pads pressure to the rim.
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Old 10-31-05, 04:42 PM   #7
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I used to be bordered with chatter, but not anymore.
What was the solution for me was a good headset that doesn't loosen up all the time.
It seems to me that a standard 36/45º alu cup design like Ritchey and Cane Creek just don’t do it.
If you're able to mount a fork mounted cable stop like Darkmother's mention, I think that's a very good idea too.
If the headset loosens, when if it's a Ritchey, Cane Creek or any other standard 45º cartridge type,
the fork wobbeling wont interfere with the brake pads pressure to the rim.
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Old 11-01-05, 12:27 PM   #8
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What headset are you running? Sweet looking ride BTW.

Quote:
Originally Posted by Lectron
I used to be bordered with chatter, but not anymore.
What was the solution for me was a good headset that doesn't loosen up all the time.
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Old 11-01-05, 02:12 PM   #9
ccharles
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Thanks for all the feedback, everyone. I will first try adjusting the toe-in on the brakes. I don't think it is a matter of a worn headset since I just got the bike this year. I did replace the brake pads, and don't remember the chatter from when I first got the bike, so it sounds like that could well the problem (the pads being out of adjustment). Adjusting cantilever pads is such a pain in the butt.
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Old 11-01-05, 03:22 PM   #10
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Originally Posted by darkmother
What headset are you running? Sweet looking ride BTW.
Thank you Darkmother.

I'm running Syncros Hardcore all stainless steel headset (CK on the other bikes).
It's heavy as ****, but tighter then you'd ever want your girlfriends *** to be.
And most important. It does not loosen up. Well. Neither does the CK, but it's not that tight.

I experience chatter with the Airborne, not much but still, but never with the Specialized.
Same fork, same brakes, same brifter, different headset.
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Old 11-08-05, 02:34 PM   #11
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Just to follow up with this, I adjusted my front brakes to have as much toe-in as possible without rubbing on the rim, and this seemed to solve the problem, I haven't experienced any chatter since then. Thanks again to everyone for their helpful suggestions.
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