[QUOTE 3581499, member: 9609"]Is there any compatibility issues between the shimano HG variations, ie HG20, HG50, HG70 etc ?
and I take it all these cassattes fit the freewheel hubs ?
The front small chain ring is knackered, so will be replacing (i never use the big ring)
Why do you suggest new jockey wheels, ?[/QUOTE]
There shouldn't be any compatibility issues, the HG stands for hyper glide which means with that designation they would all be compatible and yes they will fit onto the same freehub.
Everything wears together if your replacing the cassette, chainrings and chain, it would be wise to replace the jockey wheels as well as the new chain will probably not ride on the worn ones as good and affect shifting.