David Snyder (Ahem, no proper sign off with City & State....) wrote:
<< I finally bent each side of the springs inward several mm using some twisting action with a pair of pliers, off the bike. I measured and reduced the static pre-load by about half.
I was really surprised how much the power improved, especially from
the hoods! It used to take much of my strength just getting the pads to
the rim, but now a good pull (more like a twist) from the tops
translates into stoppage and it's plenty of response for paceline work.
>>
I agree! Here's what I just wrote to Kyle Brooks (I should have hit "reply to all")
"While the actual spring rate. i.e., strength of the "springiness", cannot be changed easily, the spring itself can be bent so as to exert less (or more) pressure on the brakes arms.
This is not done with a punch or screwdriver (!) at the pivot (that is an old and sloppy way to center the brakes in the forks)
There was a tool specifically for this which was a tube which slipped over the spring end, allowing additional leverage to bend the spring.
The principle at work here is to bend the spring ends inward (toward each other) to reduce the pressure on arms.
This is best accomplished by leaving the spring center in the channel in the brake pivot, but unclipping the ends from the grooved stubs on the back of the caliper arms. Once both sides are free, hold the calipers and grab to spring ends with needle nose pliers (or slide on that tube tool) and bend the spring inwartd toward the center of the fork.
How much depends upon the effect you want, but it is prudent to go just a little at a time to prevent overdoing it... Reassemble the spring ends in thir respective arms and try the brake action by squeezing the brake lever to see if the effect is lighter."
Dale Brown cycles de ORO, Inc. 1410 Mill Street Greensboro, NC 27408 USA 336-274-5959 http://www.cyclesdeoro.com http://www.classicrendezvous.com Giant, Specialized, Orbea, Bianchi, Felt, Litespeed, Landshark, Colnago, Townie and other exotica. National Bicycle Dealers Association Board member
-----Original Message----- From: dddd <dddd@pacbell.net> To: Classic Rendezvous <classicrendezvous@bikelist.org> Sent: Fri, 17 Feb 2006 04:26:24 -0800 Subject: Re: [CR]Was: 57mm Campy calipers.. Now: tuning Campy brakes
The deflection of metal springs is linear, unless and until the configuration is altered by gross geometry changes, hardly applicable here.
The reduction of pre-load tension follows through the entire travel. It's less of a % of the total tension as the tension increases with lever travel, but a 10# reduction remains a 10# reduction even as the pads clamp the rim.
My own experience with NR calipers had me doing everything but bending in the springs, and when that still didn't cut it I finally bent each side of the springs inward several mm using some twisting action with a pair of pliers, off the bike. I measured and reduced the static pre-load by about half.
I was really surprised how much the power improved, especially from the hoods! It used to take much of my strength just getting the pads to the rim, but now a good pull (more like a twist) from the tops translates into stoppage and it's plenty of response for paceline work. I have since done the same tweak to Weinmann and Superbe calipers with equally satisfying result, and it's never so slack as to allow the levers to rattle. Next I might try this with some 750 center pull calipers on my Pedersen, but disassembling those things to get a grip on the short, stiff springs just doesn't sound much like fun.
David Snyder
----- Original Message ----- From: "Ken Freeeman" <freesound@comcast.net> To: "'Raymond Dobbins'" <raydobbins2003@yahoo.com>; <oroboyz@aol.com>; <>
> Ray, springs are not really my field, but what you say seems to make
> sense.
> We're dealing with the stiffness of the spring wire in a bending
> deformation, and the difference between the compressive stress and
the
> tension stress is greater with greater diameter. Re-setting the
spring
> might reduce pre-load, which might reduce resistance at the idle or
> "unbraked" position.
>
> Come on, other engineers, I (a poor EE) need some smart ME's to tell
us
> what's really going on here!
>
> Ken Freeman, Ann Arbor, MI
>
>
> dale,
>
> somewhere i read instructions on how to decrease the tension of the
> caliper springs, and it involved bending each side an equal distance
using > a
> hammer and punch. but i wonder if that really does anything for the
> tension.
> my non-engineer mind thinks that the only thing that would
accomplish, is
> change the outermost position of the spring arms. wouldn't tension
in the
> springs be determined primarily by the gauge of the metal? so even
if you
> move them in, the tension wouldn't change.
>
> engineers, what say you?
>
> ray dobbins
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