Quote from jayg on Jan 4th, 2012, 9:27am:
Paul, I think I gave the wrong impression with my comment. I have never used a chain wear gage before, and was not familiar with how they worked and the units of measurement of the .75 and 1.00 readings. The intent of my comment was to relate to others, who may have been as much in the dark as I was, what I had learned. Now that I have several "keeper" bikes, I'm going to have to pick up one of these gages the next time I go to Performance. By the way a webpage for a gage of similar design to the Spin Doctor gage lists it as a "feeler" gage.
Well pointed out, Jay! I modified my earlier posts to put "%" after the numbers... Of course, it doesn't say that on the gauge itself, either!!! The concept as I understand it (courtesy of the late great Sheldon Brown, my namesake), is that as the roller pins wear, the link centers essentially move further apart under tension, and don't precisely match up with the sprocket teeth any more, eventually resulting in additional tooth wear on the sprocket... and if the sprocket gets too worn, the old chain will start to slip, and a new one will really slip...
http://sheldonbrown.com/chains.html At the bottom of the Sheldon Brown article, there is a link to a very cool article on chain wear and measurement gauges, that shows that most gauges give a greater wear indication than is actual...
http://pardo.net/bike/pic/fail-004/000.html#shimano-tl-cn40 Paul