Originally Posted by
pdlamb
My normal routine is to use a chain gauge (coincidentally, the CC-3.2 @
Kontact mentioned) to find out if it's time to break out the ruler. However . . .
Using a ruler isn't automatic. I'll go with a longer rule, such as a measuring tape or the Park SBC-1, so I can center the beginning (1" on the tape or the triangle on the Park) on a rivet. Measure to the center of the '12" rivet', then go back and make sure the beginning mark didn't shift. Repeat at least one more time to make sure you've got the right measure. Or you can measure to one end or the other of the rivet, if you're not sure you can eyeball the middle of a rivet accurately.
And then go measure another one or two 12" sections of chain, to see if the measurements match or are longer than you want the chain to be to stay on the bike. If there's significant divergence, go with the longer measurement IME, and replace the chain.
IIRC the Pedros tool is supposed to take roller slop out of the measurement, FWIW.
My guess is that your "ruler" moved while you looked from one end to the other. That's one free opinion that's worth everything you paid for it!
I think you've just shown why chain checkers exist and should be used by most people. To do an accurate measurement with a ruler - if the user even knows about the ruler method - means the person has to be aware of how to use a ruler, commonly starting at 1" on any ruler, not just tape measures. At least that's the way i was taught in various shop classes in Jr. High. Also the user has to be aware of the potential pitfalls as you've well described. It's actually not a trivial thing to measure from "pin to pin" - they're tiny and hands aren't necessarily steady.
You, I and probably a significant portion of bikeforums denizens know this (but not all of us knurds). The typical bike user, even racer and enthusiast, doesn't know and probably doesn't care about mechanical stuff or know this stuff. So chain checkers serve a really good purpose for almost anyone who wants to know the status of the chain.
If I've cleaned a chain (mineral spirits bath) I hang it from a little nail on the edge of a shelf in my garage to dry and go ahead and measure with a ruler. If it's on the bike, every once in a while I use the Park CC4 or Pedros Chain Checker Plus II (I have one at home and the other in my travel bag.) I'm not much of a scientist so can't really tell you how the two methods compare. But if one or the other makes me think I need a new chain, I get one.