Originally Posted by
stedalus
I've read that it's 5 mm C-C between rings, and that's what I measure on my cranks (one 9 speed, one 10 speed). Admittedly this is with a ruler and some squinting as I don't have calipers here, so maybe I'm off.
The best way to measure the spacing require the crank to be removed, placed on a flat surface and a measurement taken from that flat surface to the tip of each tooth, then figure the difference. It will be very close to 7.5mm. Sheldon Brown mentions 5mm, but he's wrong. Even the new 11 speed cranks are very close to 7mm, with the big ring moved .6mm closer than before.