Specialized Rear Road SL Thru-Axle

The number that matters here is 165mm. Specialized has used more than one rear axle length across its disc road bikes, and the Road SL Rear Thru-Axle from Specialized is the 165mm one: alloy, bolt-on, 12x142mm rear hub spacing, M12x1.0 thread pitch, and a 6mm Allen head recessed into a conical seat. It is the axle the bike left the factory with, sold on its own as a service part.

Fitment runs across most of the current carbon road and gravel range. Aethos and Aethos 2, Tarmac SL8 and Tarmac SL9, Roubaix SL8, Crux 4, Crux 5, Crux DSW, and the current Diverge all use it, which is the practical upside of Specialized standardizing the rear dropout interface across race, endurance, and gravel platforms. If you own two of those bikes, one spare covers both.

Check what you are replacing before ordering. Older Specialized disc road frames, including the Tarmac SL7, Roubaix through 2023, Allez Sprint, and Turbo Creo 2, take a 168mm axle, and other models use a 169.5mm axle with a 5mm hex. Thread pitch is M12x1.0 on those parts too, so a wrong-length axle will start to thread and feel close to correct while leaving the hub either under-clamped or bottoming out early. Measure the old axle end to end, or match the part number against the replacement parts listing for your specific model, and you will not have to guess.... Read More