Joined: Jul 2002
Posts: 40,863
Likes: 3,116
From: Sacramento, California, USA
Bikes: Specialized Tarmac, Canyon Exceed, Specialized Transition, Ellsworth Roots, Ridley Excalibur
I believe the axle moves roughly 1/8 in. per tooth difference. As FiftySix said, unless you're right at the limit, it's fine to use the same chain. In fact, that's why most SS/FG hubs are flip/flop. You can change the gearing by flipping the wheel.