OH! re chain rings and compatibility (the original question, having drifted sideways quite a bit).... Shimano chain rings have an "A" and a "B" version, some are A, others are B, and I'll be darned if I know what distinguishes them.... I suspect it has something to do with ramping and pinning. You should use A rings with other A rings, and B rings with other B rings for the best shifting. the letter should be stamped on your existing rings.

hmmm. http://techdocs.shimano.com/media/te...9830728283.pdf doesn't indicate if a M660 is A or B or what. maybe this only applies to road bike rings?


anyways, if you're running in the middle of your cassette now, you're probably fine with the rings you have. if you wear out your cassette, you might consider replacing it with one that starts with a 13 instead of an 11, this will give you closer gear spacing in the mid ranges, and you might also run 44:20 instead of the 32:15 (its the same gear, but with the bigger ring there is less drive train loss and wear). ditto 44:24 instead of 32:17.