If you've ever wanted to run one set of wheels on your enduro bike and your downhill bike, apparently you're not alone. After offering kits to convert 15mm road forks to fit (more common) 12mm hubs
, Forkmods say that "a sufficient number of people" asked them for a kit to convert 20mm thru-axle MTB forks to fit 15mm hubs.
Interestingly, RockShox seriously considered using a 15mm axle when they last updated the Boxxer in 2018
, so Forkmods is not the only company to see the benefit of cross-compatibility.
The kit consists of an aluminum reducer sleeve which slides into the non-threaded dropout of the fork, and a thread adapter for the threaded (brake) side, which has 20mm male threads on the outside and 15mm female threads on the inside. A 22mm socket is used to torque the thread adapter into the fork threads. Steel inserts slot into the inner side of both dropouts to interface with the 15mm hub end caps. Then, a 15mm aluminum thru-axle slots through the fork and hub.
"The install takes very little time and is entirely reversible," according to Forkmods, and once you've installed the adapters you can remove and install the wheel just using the 15mm thru-axle and Allen key as you normally would.
Stiffness may be a concern when going from 20mm to 15mm, but the stiffness of a fork has less to do with the thru-axle than you might think. That's because the immense clamping force provided by a correctly torqued thru-axle creates a strong friction interface between the hub end caps and the fork legs. This means the hub acts like a structural component of the fork, so long as the axle is done up tight enough. When RockShox launched the latest iteration of the Boxxer, they told me they could have made the Boxxer just as stiff with a 15mm axle. They chose to stick with 20mm because most purpose-built downhill wheels are 20mm only.
But now that enduro wheels are often just as tough as downhill wheels, and many riders are running downhill tires and big rotors on their enduro wheels, some riders might want to share one front wheel across their downhill and enduro bikes. And as it's reversible, you can always go back to a downhill-specific wheel later on.
Three kits will be offered:
• Kit A: Fits/replaces RockShox Maxle Lite/DH Front Thru Axle: 20x110, 165mm Length, M20x2.0 thread, 35mm/40mm Chassis (2011-2016 Domain, Lyrik, Totem), SRAM part #: 00.4315.013.030 & 00.4315.013.040.
• Kit B: Fits/replaces RockShox Maxle Lite Front Thru Axle: 20x110, 158mm Length, M20x2.0 thread, 32mm Chassis (2011-2016 Argyle, Reba, Revelation, Sektor, Pike, Recon, Tora), SRAM part #: 00.4315.013.010.
• Kit C: Fits/replaces Rockshox Maxle DH Front Thru Axle: 20x110, 158mm Length, M20x1.50 thread, BoXXer 2019+ SRAM part #: 00.4318.027.000
On compatibility, note that Boost 15x110 and Boost 20x110 forks both have a wider brake rotor spacing than either 15x100 or conventional 20x110 (non-Boost) standards. Therefore, a 15x110 Boost hub won’t fit in a 20x110 non-boost fork.
The price is expected to be around $110 USD when the production kits become available. Check out forkmods.com
for more info and updates. But be quick if you want one - acording to the company's website, "If even half the people who have begged us to make this conversion order one, they'll be hard to come by for a while."