I've got a '97 Bianchi Trofeo with an eight speed Campagnolo drivetrain. I'm happy with the eight speed part, but would like to replace the 39/52 crankset with a 34/50. I've got a nine speed Shimano Tiagra 34/50 crankset with BB. Should I be able to swap the cranksets? Would it require a different FD?

A similar question was posed on the Road forum, but I'm guessing you guys might have more experience at this.

Thanks!

will work - will need a tune.

Yes, just move the FD down. The BB I don't know about, My Ciocc I went from a Victory crank to a Mirage compact and used the old BB. What crank are you using.

+1

You might have trouble with an 8-speed chain on a 9-speed crank. 9-speed chain on an 8-speed cassette should be OK though.

Wouldn't the nine speed chain be too narrow for the eight speed cogs?

Nope. The cogs are closer together on 9 speed so you need a thinner chain, but the teeth aren't thinner.
If your chain is too wide in front though, you can have all kinds of shifting problems depending on the brands of crank and front der.

DiabloScott is correct.

Okay, I get that. I was hoping that, since the Campy FD kinda ratchets the chain over rather than just thunks it over like Shimano, it wouldn't be an issue.

You can't always trust the manufacturers or even Sheldon on some of this stuff... there are just too many variables.

I had a 9-speed chain that never worked right with my 8-speed compact crank - it'd skate or get caught between the rings - no amount of futzing with it helped... gave up and bought a new 8-speed chain and it worked fine again.

I have a 10 speed cassette (ultegra), shifters (DuraAce) and chain (shimano) that work just fine with my 9-speed Dura Ace crank, FD, and RD... Shimano says I need a 10-speed crank but I've had zero issues with front shifting.

But narrower chain on the rear is almost never a problem.