Mavic's Crossroc XL 27. 5 Wheelset is designed for Enduro focused riders around the world. With the new breed of super bikes on the market, all using 27. 5in wheels, the Crossrocs are a great option for hard riding, and big races like Andes Pacifico or Trans Provence. The Crossrocs are UST certified, meaning you can run any UST tire, and seat it with a floor pump no need for a compressor to get the tire to sit in there. The rim material is Mavic's S6000 aluminum, which is a hair heavier than the Maxtal alloy you'll find in the Crossmax line, but certainly light enough for racing. Wrapped around the rims are Mavic's Crossroc Quest tires, a medium durometer tire designed to shed mud and perform in broad conditions. At the center of the rear wheel is Mavic's Transfer System 2 hub, which forgoes the four pawl construction of the Crossmax line for a simultaneously engaging two pawl setup. You'll still get rapid engagement, so ratcheting through rock gardens shouldn't be a problem. The hubs are compatible with ShimanoSRAM nine and ten speed cassettes, as well as Shimano 11 speed. A SRAM XD Driver retrofit is available separately.