20mm through-axle front hubs are a well-established standard for DH and freeride applications, but with XC/trail forks still getting longer there are plenty of 140/150mm front ends out there that rely on the venerable QR skewer to hold everything together. And frankly it’s just not up to it. QR-equipped long travel forks might feel OK, but swap to an equivalent fork with a through-axle and the difference is clear. It’ll be considerably stiffer, enhancing control, and there’s no chance of a loose skewer leading to your front wheel coming adfift.
There are downsides to 20mm, though. The big axle means big hubs and plenty of metal on the forks, which all adds weight. Working on the basis that much of the stiffness (and all of the security) benefit of through-axles is due to the axle passing through a closed “dropout” rather than the diameter of the axle, Shimano and Fox have introduced a new, lighter, standard aimed at all-mountain and XC use.
The new standard, seen here on a Fox 32 TALAS fork, uses a 15mm diameter axle while retaining the 100mm over-locknut dimension of conventional hubs (20mm hubs are 110mm wide). Shimano’s testing suggests that stiffness is close to that of a 20mm setup and streets ahead of a 9mm/QR arrangement – 15% stiffer torsionally and 25% stiffer in transverse shear – while the smaller hub shell and ability to stick with existing fork widths thanks to the conventional OLD saves a chunk of weight over 20mm.
In use the 15mm system is a little like SRAM’s Maxle setup, with an axle that threads in to one side of the hub and has a QR-style lever to lock it all in place. Unlike Maxle, though, the threads in the hub are actually a splined insert, so you can adjust the final lever orientation by moving the insert round so that the thread starts in a different place. The lever cam exerts a clamping force on the outside face of the “dropout” to lock everything in place, rather than Maxle’s expander that wedges itself inside the dropout.
We don’t know as yet which Fox forks will feature the new system, although at the very least it’ll surely be found on all the 140mm 32 models. We’d like to see it as an option on everything, though – we can’t see why anyone should have to stick with QRs just because they run 100mm travel forks. Shimano will have a bunch of hubs and wheels ready for the new system, with a XTR and XT level hubs being available in June. The HB-M978 is an XTR 15mm hub that’s 100g lighter than the existing M976 20mm model. XT-level hubs will be available with Centerlock or six-bolt rotor mount options. And in September there’ll be a new Deore XT front wheel with a 15mm hub.