Originally Posted by
bobotech
Now that you say that, I think you are right. I have seen others mention that you can use front double and triple cranksets designed for 9 and 10 speed bikes with 6-7-8 speed chains.
I tried to use an allegedly "9 and 10 speed compatible" crankset with a 9 speed chain and found that I didn't have any usable overlapping gears due to the chain rubbing on the big ring until I shimmed the small ring inboard to 9 speed spacing.
More speeds means narrower cogs, narrower chains, and tighter spacing in the front rings.
5-6 speed chains are 7.4-7.6mm wide
8 speed chains are 7.1-7.4mm wide
9 speed chains are 6.6 - 6.9mm wide
10 speed chains of current production are 5.9mm wide (Campagnolo started at 6.1mm)
11 speed chains are 5.5mm wide