From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.racing
Subject: Re: Chain skip
Date: 6 Apr 1998 16:03:44 GMT

anonymous writes:

> I changed my chain even though it wasn't "stretched" more than 1/16"
> over 12 inches. It might have been "stretched" 1/32". Anyway, I wanted
> the new chain by Sachs with the Powerlink so you can take on and off
> easily for cleaning. The chain skips on the 3 most used cogs when
> accelerating slightly.

> This was the original cassette and chain....SHIMANO ULTEGRA.

If your measure is accurate, I suspect you are running with low chain
tension.  Either that or the Ultegra sprockets are more sensitive to
wear than most.  As the chain wears, it rides higher on the sprocket
tooth and rolls off under load.  A new chain has the same pitch as the
sprocket and rides lower in the sprocket.  If there are wear ramps in
the sprocket, a new chain will try to ride up into those pockets that
lie at a greater circular pitch, making it impossible for the incoming
links to engage fully.

When you consider material elasticity, chain drive becomes a
complicated concept that probably looks more like something that
doesn't work.  Essentially only the last couple of teeth carry most of
the load.  This becomes apparent when you visualize the components as
being made of various hardnesses of rubber, a valid concept although
the elongation of metals are microscopic.

Jobst Brandt      <jbrandt@hpl.hp.com>