Originally Posted by
_ForceD_
The bike in question in my OP isn't currently using a crown-mounted stop. But...I know it's drilled for one becasue I recall looking at the hole and thinking that I could mount a spare side-pull caliper on it (but obviously didn't cause it'd leave the canti lugs weirdly exposed). Although the smaller pads have mostly eliminated the shudder...I've told the kid that I want to properly correct it...told him to bring the bike next time he's home from school.
Still the cause/correction is baffling to me. I just don't see how moving the cable stop from the steerer to the fork crown eliminates the shudder.
Dan
The way I understand it:
When you apply the brake, the fork and steerer below the head tube flex a bit. If the cable is hung from way up high on the stem/steerer above the head tube, which doesn't flex, the flexing of the fork and steerer below changes the distance between the hanger and brake (very slightly) which alters the tension on the cable and changes how aggressively the brake pads are grabbing the rim. This change in tension causes the brake to grab more aggressively then quickly release as the fork flexes back.
By lowering the cable down onto the crown, the mounting point is much closer to the brakes, so when the whole thing flexes, the distance between the hanger and brakes stays the same (or at least changes a lot less), so the pressure applied on the rim stays more consistent.