kirke

So my seat tube is 28.6mm, but practically all modern front derailleurs are 31.8mm. What would be better to use in terms of a solid attachment, least likely to shift around: using a shim with a clamp-on 31.8mm front derailleur or using a braze-on adapter with a braze-on front derailleur?

Thanks!
-Kirke

Zouf

Problem Solvers makes a 28,6mm braze-on adapter which should do the job just fine. That's a lot better than fiddling with a shim that's always slipping at the exact moment you want it to stay in place.

BCRider

About two years ago Shimano went to a "one size fits all" front derrailleur that comes with a bunch of plastic shim bushings to fit to other size tubes. Any of your local bike shops will hopefully have a box full of the excess bushings. If your derrailleur isn't one of those I'm not totally sure if the bushings will fit correctly. So take yours in and try it before you leap.

HillRider

If you haven't already purchased the clamp-on fd, buy the adapter and a braze-on fd. The adapter is a one-time purchase and any braze-on fd will fit.

Actually, most clamp-on clamps are 34.9 (aka 35 mm) these days.