31.8 mm front-derailleur clamp (31.8 mm band)
Which frames use a 31.8 mm band front-derailleur mount, and how to tell band from braze-on.
Published dimensions
| Mount / band size | 31.8 mm (1 1/4 in) seat-tube clamp |
|---|---|
| Designation | 31.8 mm band |
| Typical frames | the most common round-tube clamp size on aluminium road and touring frames |
Used on: the most common round-tube clamp size on aluminium road and touring frames.
31.8 mm is the mainstream clamp band size for a 1 1/4 in round seat tube. A Shimano SM-AD91 braze-on adapter is a 31.8 mm clamp that ships with a shim to 28.6 mm. It will not fit a 34.9 mm oversized tube without the larger band.
Frames and related mount sizes
Front derailleur mount on a Cannondale CAAD13 (2020 on)31.8 mm band28.6 mm front-derailleur clamp28.6 mm band34.9 mm front-derailleur clamp34.9 mm bandBraze-on (direct-mount) front derailleurbraze-on tabBSA bottom bracket shellthe frame's other threaded interfaceT47 bottom bracket shellthreaded BB, same frame
SOURCES: BikeRadar, Front derailleurs explained: types, mounts and compatibility · Shimano, SM-AD91 front derailleur clamp band adapter