Re: [CR] Brakes and flex


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In-Reply-To: <AANLkTimpQiQSWYRYh5k=gnt7Jhrsce27pTYKCz58jH6B@mail.gmail.com>
References: <1AF44DEDBB574D42885E6BF8375640B8@gateway2v8e13w>
Date: Tue, 4 Jan 2011 17:33:29 -0800
To: Harry Travis <travis.harry@gmail.com>, Charles Nighbor <cnighbor1@comcast.net>
From: Jan Heine <heine94@earthlink.net>
Cc: classicrendezvous@bikelist.org
Subject: Re: [CR] Brakes and flex


At 8:53 PM +0000 1/4/11, Harry Travis wrote:
>My uninformed belief is that we've never seen measurements or images clearly
>pointing to where the "give" is in the bicycle braking system, so it is
>mostly attributed to the wrong parts.

You can see the flex in truly flexible brakes, especially if you use relatively thick pads. You squeeze the lever hard, and instead of the brake blocks mushrooming from the pressure, the upper arms move (on a sidepull), but the lower ones don't. The brake blocks are not deformed.

You could even measure this: How much the cable is shortened and how far the brake pads travel, once with the rim removed (so you get a measure of the mechanical advantage), and once with the rim in place (so you get the flex). Using the same and relatively soft pads, you could compare different brakes.

On the road, you notice brake flex as follows: The brake feels fine, even great, at first. Then you brake harder, and even though you pull harder and harder on the lever, the brake power at the rim does not increase commensurably. Eventually, you bottom out the lever on the handlebars, and still don't lift the rear wheel.

Obviously, riders who never brake very hard won't run into trouble even with flexible brakes. And often, those riders then vehemently disagree with tests in which we report that the brakes flex too much.

Housing compression should provide the opposite feel: At first, it's a little mushy, until you have compressed the housing, and then (if you have brake lever travel left), the brake is fine.

Jan Heine Editor Bicycle Quarterly 2116 Western Ave. Seattle WA 98121 http://www.bikequarterly.com

Follow our blog at http://janheine.wordpress.com/