A Trek FX fitness uses a Braze-on (direct-mount) front derailleur for the front derailleur. The dimensions, how to confirm it on your frame, and how it compares to the neighbouring standards.
Updated 05 September 2026.
What front derailleur mount does a Trek FX fitness use?
The front derailleur fitment standard on a Trek FX fitness, and how to pick the right part.
| Frame | Trek FX fitness |
|---|---|
| Front derailleur mount | Braze-on (direct-mount) front derailleur (braze-on tab) |
| Mount / band size | no clamp, bolts to a frame tab |
| Typical class | carbon and higher-end aluminium road, gravel and MTB frames with a moulded or welded derailleur tab |
The Trek FX fitness uses a IS42 integrated upper headset (integrated, 42 mm), a 27.2 mm class seatpost, a 12x100 mm front thru-axle at the front (12 mm x 100 mm, front) and a braze-on front derailleur.
The 27.2 mm figure is the mainstream disc-road interface; many of these frames ship a proprietary aero-shaped post, so confirm the exact part. The bottom bracket is covered on its own page.
SOURCES: BikeRadar, Front derailleurs explained: types, mounts and compatibility · Shimano, SM-AD91 front derailleur clamp band adapter · Park Tool, Standardized Headset Identification System (SHIS) · BikeRadar, Road bike axle standards: the complete guide
Questions and answers
What front derailleur mount does a Trek FX fitness use?
A Trek FX fitness uses a Braze-on (direct-mount) front derailleur for the front derailleur.