9-speed chain with a 10-speed rear derailleur?

[kenw]

Shifting is friction. Is there enough clearance
between the 10s cage plates for the 9s chain? Derailleur will be mid-cage,
if that is of any interest. Thanks in advance. Ken

[Auk]

You'll be fine. Been running a 10spd Campy setup with a 9spd chain and cogs for years. Same goes for the Shimano setup I have on a couple other bikes. And, at the risk of getting beat, I even run this setup on a SRAM Rival setup. Shifts just fine on all three.

[gone]

No problem. Used a 10 speed rear derailleur (Shimano) with a 9 speed STI setup for thousands of miles. Worked great.