Originally Posted by
HillRider
8-speed cranks have a slightly larger gap between the chainrings than 9-speed cranks which have a very slightly wider gap than 10-speed cranks. AFAIK, the difference from 8 to 9 is greater than the difference from 9 to 10.
When 9-speed first appeared Shimano advised you could use an 8-speed crank with the new 9-speed chain if you "shifted sitting down", i.e. if you shifted the chainrings while the chain was not under a lot of tension. Otherwise, the chain may tend to "skate" on top of the smaller chainring instead of completing the shift cleanly.
I'm running a 9 speed set-up on a 8 speed crank. I have to be careful downshifting under load, otherwise the chain will jam in the gap between the middle and small chain-rings. Other than that, it works fine. Most of the time I remember to take it easy when down shifting.
