Originally Posted by
Jeff Wills
You may need a 0.5 to 1mm washer on the axle's drive side to space the small cog away from the dropout. Older frames often have pieces/parts in that space. Newer cassette hubs count on that space being clear of impediments.
If you're running an eight-speed cassette, you need an eight-speed chain.
Or, if necessary, you can add .5mm spacer and run a 9 speed chain with 8 speed cassette. I had to add the .5mm spacer and a 9 speed chain with 7 speeds to get just enough clearance.
John