Originally Posted by
DaveSSS
Be sure that you understand the 43.5 and 45mm dimensions that you have referred to. The 43.5mm dimension is to a point in space, centered between the rings. Why this is used, I have no idea, since it's stupid to dimension to a point in space. With typical 7.5mm chainring spacing, that makes the tip of a tooth on the big ring 47-48mm from the center line of the ST. That is something you can measure.
The 45mm dimension is normally to the tip of a tooth on the middle ring of a Shimano road triple. FSA cranks are 46mm. The tip of a tooth on the big ring would be another 7.5mm further to the right.
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.