From: jobst.brandt@stanfordalumni.org
Subject: Re: Fixed gear converter?
Newsgroups: rec.bicycles.tech
Date: Fri, 28 Dec 2001 04:02:02 GMT

Brake cable failure.

I was fortunate to have one of these early in my bicycling career and
in a relatively innoccuous place.  I was entering a left turn lane
with three or four cars waiting for the light to change, heavy traffic
crossing in front of them.  As I rolled in, my front brake cable
failed as I came up on this column but I was able to stop before the
stop line using my rear brake, passing the cars on the left.  The
outcome, had I not had another brake was vividly apparent, and I took
the hint.

Instead of just buying a new cable and be done with it, I took the
broken cable home to analyze the nature of this tensile failure.  What
I found was interesting and enlightening about when to change brake
cables.

Brake cables wear fastest at the tightest bend, so only this place
needs inspection.  Since the cable is helically wound, as it must be
to be constant length, all strands wear the same, all being on the
inside of the curve at some part of the cable stroke.  Therefore, all
strands wear out at the same time and all strands break even though
most of the cable seems to be in tact.  What's more, when strands are
worn about 1/3 through their diameter, they develop a brittle
relatively flat wear surfaces with micro-cracks.  Although most of the
cable cross section is still there, the cable becomes dangerously
weak.

For this reason, brake cables are best replaced when the strands
develop visible flat wear surfaces on the inside of a housing curve,
or at calipers or hand levers.

The finer the strands, the sooner the cable needs replacement.  I
believe an optimum strand size has been pragmatically discovered long
ago and that it is about what older Campagnolo and Shimano brake
cables have.  I don't know what inexperienced engineers have wrought
at these companies today.

Jobst Brandt    <jobst.brandt@stanfordalumni.org>