I’ve found some compact cranks that I would like to put on my wife’s bike. Her drivetrain is a 7-speed Shimano RX100 system with very very low mileage for its age. The cranks say they are 8-9 speed compatible. Would they work with a 7 speed system?
yes.
I thought as much but I thought I would ask before tearing everything apart.
I really don’t think there is much difference between 7 and 8 speed systems. It’s been a while since I’ve run an 7 speed cassette but the 8 speed cassettes seem to sort of retrofitted from 7, with another cog screwed on to the end of it. The spacing is the same. The hub is a little wider to accommodate the extra gear. Add another click to the shifter and the industry pushed 7 into obsolescence.