Bicycle Mechanics - 9-speed chain on 8-speed cassette

Can I use 9 speed chain on/with an 8-speed cassette?

The chain I currently have is a 6/7/8 speed chain and rubs on the large chainring when it's in the smaller chainring (in certain gear combinations). The double crankset doesn't seem to like the wider chain - I think it's 9-speed compatable. Would like to change it to a narrower chain to make the rubbing stop. But not sure if the 9-speed chain will interface properly with the 8 speed cassette.

This is normal, rubbing on huge cross chain combos. Also you can trim your FD if you are running STI or downtube shifters.

Do not buy a new chain until you have figured out exactly what you're doing that is causing the rubbing and without trying other 0 cost solutions first. You should not blindly change out the chain. The crankset will have hardly anything to do with the "speed of chain" you can run.

Do you have a 9 speed rear cassette?

And to answer your question yes a 9 speed chain should work on 7/8 setups.

Hey, when you're in the small, small combo, why don't you just half-shift the FD? Just nudge it up an bit when you hear the noise and your problem is solved.

I should have been clearer. When the current chain is in the small chainring (it's a double crankset), the outside of the chain is rubbing on the inside of the next chainring, not rubbing on the derailleur. Trimming has no affect.

Also, the chainline is bang-on. Front and rear matches perfectly.

I assume you have 53/39 chainrings. What you are experiencing is common with that chainring combination, particularly if the bike has short chainstays. I further assume it rubs only when the small chainring is used with the smallest two or three cogs. Some cures:

1) Don't use the offending gear combinations
2) Replace the 39T with a 42T ring.
3. Get a frame with longer chainstays.
4) Get a longer bottom bracket.

Of these, #1 is the cheapest. A 9-speed chain may help but the chain width is only very slightly less than an 8-speed chain.