Originally Posted by
Clem von Jones
Yeah, according to Sheldon Brown's website various 8, 9, and 10 speed parts are compatible. It might be desirable to run wider chains in certain situations for example with my 8 speed era crankset.
https://sheldonbrown.com/speeds.html
An 8 speed chain on a 9 speed cassette is not going to work very well. It is too wide.
8 speed crank with an 9 speed cassette needs a 9 speed chain.