If I remember correctly (which isn't assured) Bio-pace mtb cranks used classic 110/74 BCD. If so, the minimum size rings are 24 and 34t (maybe 33t) respectively. But that's for round. The shape of a Bio-pace would increase the minimum size somewhat, but don't ask me how much -- it was a long time ago.
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Last edited by FBinNY; 09-20-14 at 06:08 PM.