Quote: Originally Posted by
tafi .
Front brake chatter is entirely down to stiffness (or lack thereof) in the fork steerer tube. Lennard Zinn has given a good explanation of the source of this.
http://velonews.competitor.com/2010/09/cyclocross/technical-qa-with-lennard-zinn-return-to-cross_101807
Basically when you brake the fork begins to flex slightly under the bike. If the front cable stop is at the top of the headtube, this flex pulls tighter on the brake cable, in turn pulling the brake on harder and causing the fork to flex under more. Eventually the brake is pulled on so hard that the friction point between pad and rim is what gives out causing the bike to lurch as the flex suddenly unwinds and the brake releases a bit. The process then starts
FWIW. Lennard Zinn's how-to books are certainly amongst the best ... and, he is a
font-of-knowledge ...
- and, of course, I certainly don't ride a larger frame where chatter is a significant problem ...
- regardless, if one thinks about it then one would think that the longer head tube would actually make the steering column MORE stable!
I'm not saying that Zinn is wrong in why he believes that
chatter occurs on the CX bikes which
he sets up ... but, I have learned to take what he promulgates in his
VeloNews columns with a
grain-of-salt ...
Regardless, I must point out that the way Zinn appears to set up
his CX bike harkens back to the early days of cantilever brakes ([COLOR= #808080]
i.e.,
the 80s, AFAIK[/COLOR]) where the cable was often fed through a hole in the stem! Instead, of course, Zinn apparently uses a hanger that must ([COLOR= #ff0000]appears to!?![/COLOR]) attach to the stem's face plate ... THAT's got to be even worse than the
intermediate pass through which a hole drilled in the stem provided ...

WTF?!? I could be wrong, but it looks as though the location which Zinn prefers for his cable hanger places an unnecessary, exacerbating "tension" on his cantilevers AND ([COLOR= #808080]therefore[/COLOR]) the fork by not having the hanger feed the brake cable as close to parallel to the head tube as possible:

Talk about aggravating a potential weakness in the overall design!
- someone more clever than I am can perform the actual vector calculations if it matters to them ...
I will suggest that Zinn could mitigate the
chatter on the CX bikes which
he sets up by changing to a brake cable hanger which runs the brake cable closer-to-paralle than the hanger he prefers to use ... AND, as I previously suggested, the
chatter induced by "oscillation" can probably be reduced by using a thicker straddle cable ... AND, on Zinn's bike(s), the "oscillation" can be probably be mitigated by shortening the straddle cable, too! Again, WTF is Zinn thinking with his straddle cable setup?!?
---
BTW. As I noted, previously, I can live with what I referred to as
pseudo-modulation on the rear brake ... From viewing-up-close a handful of bikes set up by one bike shop that is local to me, that shop's Wrenches prefer to set up "regular" Road brake calipers with the pads as close to the rim's braking surface as a V-brake pad needs to be when used with regular Road levers! One guy I know says he likes THAT configuration because he says that he likes to "pulse" the brake levers to stop ... Really?!?
- maybe he had glazed pads on one of his bikes in the past, so the hard clamping of the pads against the rims is reassuring to him!?!
Well, I suppose I don't have a deft enough touch to "pulse" my brakes in order to come to a controlled stop ... And so, I prefer having
modulation over the comparatively hard clamping which having the pads mounted to the brake surfaces results in ...
- basically, modulation is the difference between an on-off switch and a rheostat ...
- or, turning a shaft using a knob attached to the shaft vs. turning just the bare shaft ...
- et cetera.