Originally Posted by
DaveSSS
Temperature is not relevant when measuring only a 12 inch length. A 10 degree change would expand the length by 0.0008 inch. Just get a 12 inch machinist's rule and place one end on the edge of a pin. The pin at the other end will be completely covered when the chain is new. When 1/2 of that pin is exposed, you have a little over .5% elongation. As I've already noted, some chains will show little elongation even when severely worn, so the elongation measurement may be worthless. That's why Campy suggests measuring with calipers between outer plates to a length of 132.6mm. It deliberately adds roller wear to elongation. The roller wear is greatest on the hole in the roller.
This is one of the things that bothers me about people who say to use a 12” rule. Yes, a chain is “
exactly” for 24 links...although how much variation is in
that measurement. But if you are trying to be so accurate, how do you measure about 12” + 3/32” on a rule that is only 12” long? That is as much of an estimate as the chain checker tools give. “When 1/2 of that pin is exposed” is even less accurate.
Generally speaking, the chain checker tools are good enough. They don’t tend to overestimate chain wear which would lead to drivetrain damage. They actually tend to underestimate the chain wear. If they do underestimate the wear, how much of an impact does that have on the mileage that one can get out of a chain? 100 miles? 200 miles? I really doubt that it would be a significant decrease in chain mileage.