I've Googled and searched the BikeForums, but haven't yet found a straightforward answer. I find TONS of info on measuring BCD and lots of info on measuring chain width, but little to nothing on determining the width of a specific chain-RING, and what drivetrains it's appropriate for.

First - I have a bunch of chainrings and a good caliper. Where and how do I measure the width of a chainring? I'd assume at the base of the teeth and not on the "shoulder" below the teeth?

Second - What widths will work with what drivetrains. I'd assume that any ring of X-width would work with any drivetrain with a >X-width chain? Therefore, a nine-speed chainring would also work with 8, 7, 6, and 5 speed rear ends?

Third - What is the MAXIMUM width that will work with 7, 8, 9, 10, and 11 speed (specifically) rear cassettes without chain suck?

I'm sure this info is available somewhere, but in 30 minutes of searching, I've not yet been able to find it. I suspect that the finding depends on knowing where to look - therefore I defer to youse guys' superior knowledge.

THANKS for any help - FH