I recently picked up a Park CC-3.2 to put in my portable bike tool-bag (12 inch ruler won't fit). With it one of my chains that measures fine with the ruler, fails, even at the .75 side. Reading on the subject states that the CC-3.2 doesn't take into account roller wear, which the Shimano TL-CN41 does. So, I took a popsicle stick (perfect thickness) and shaped it to press the roller nearest the drop-in end of the Park to give similar results to the Shimano and eliminate roller wear anomalies. Sure enough, measurements come out differently, and what "failed" previously with the Park, now passes. My question(s): Is the Park CC-3.2 cut to compensate for roller wear to a point (meaning longer than it would be if the rollers were both pressed against their links in the same direction, as with the Shimano or my popsicle stick)? If so, my invention would be inaccurate. Has anyone measured with calipers (vernier) these two tools to see if they are the same distance at their measuring points?
Thanks for any insights or help.
I don't know the technical specs of how these tools work. But I'd say that in general, you shouldn't worry about it too much. Even if you know the exact percentage 'stretch' your chain has, it's really a guess as to what to do with that information. Should you replace a chain at .5% wear or .6%? The debate about whether to adjust for "wear on the rollers" sounds like BS to me. The point is that a worn chain doesn't fit the shape of the teeth on the cogs anymore. I don't think it matters much exactly which part of the chain has the wear.
On newer, high end drive trains, replacing a chain before it stretches too much will prevent you having to constantly replace the cassette as well. They are made out of much less durable materials and are much more sensitive to mixing old and new parts together. On older bikes, you can get away with a lot more stretch before it will impact anything. But there's no magic formula.
I think I'll carry the Park tool for initial checks, but then pull out a ruler for the final decision. Old school is the best school sometimes. Had just wondered if anybody had done any tests on the accuracy of the chain wear specific tools out there is all.