Bicycle Mechanics - brake chatter
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Jim in KC
05-01-06, 04:42 PM
On my first extended ride of a new bike (see: http://www.khsbicycles.com/08_urban_xp_06.htm), I noticed a distinct skip on every revolution of the front wheel when applying the brakes (linear pull). At first I thought the wheel was loose. I reinstalled the wheel, lifted the front end and pounded down on the top of it to make sure it was tight, but when I rode again, the skip was still there. The wheel appears basically true and I can't see any imperfections on the rim at the point where the skip occurs. The bike shop mechanic tells me that this is natural and caused by the rim's seam, and that after a while enough brake material will lodge there to make it unnoticable. I'd never heard of this. Is it common?
The Great Stonk
05-01-06, 05:43 PM
on lower end budget orientated rims yes, basically a bad join in the rim, their may not be a lip or a ridge in the rim, but it will be slightly thicker or thinner at and around the join...
Jim in KC
05-01-06, 06:18 PM
Thanks, Great Stonk. I was puzzled by the fact that I couldn't see or feel anything on the rim. The bike is definitely fitted out with lower end components. I bought it primarily for the frame.
05-02-06, 07:24 PM
Either a bad joint or a wavy rim or a dented rim. The dented rim would happen after hitting potholes, so I'm excluding that one.
05-02-06, 07:30 PM
It may be possible to lightly sand the joining ridge down a tad, enough to eliminate the noise but not enough to kill the structural integrity.
Jim in KC
05-03-06, 09:35 AM
Thank you, Michel and Pilatio. I think your input narrows the problem to the seam which I can see near the point on the rim where the skip occurs. I will consider sanding it. As I inspected the rim more closely I also noticed on the label the message "Warning: Subject to Wear. " I guess so.
05-03-06, 09:46 AM
Wow, if a seam on the rim is the cause, it's a poor-quality product. Couldn't chatter also come from misaligned brakes?
Jobst Brandt: "Soft brake pads and lightweight (flexible) calipers promote squeal and chatter, chatter being the mechanically more detrimental version of stick-slip behavior. Brake chatter is caused by gummy residue on the rim together with excessively flexible (skimpy dimensioned) brake mechanism." The whole article is here, on Sheldon Brown's web site: http://www.sheldonbrown.com/brandt/brake-squeal.html.
Jim in KC
05-03-06, 01:30 PM
Chatter might have been a poor word choice. When I apply the brakes while rolling down a hill, the problem seems constant. At slower speeds, it's more obvious that it occurs once every revolution of the wheel. And when I lift the front of the bike, spin the wheel, and lightly apply the brake, I can pinpoint a specific location on the rim, near its seam. If the brakes were the problem, wouldn't it occur whenever they were applied, no matter the position of the wheel?
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