Zipp's ZR1 SL is a premium lightweight hubset built for performance and durability. Modeled after its predecessor, the ZR1 hub, the SL version features a lighter hub shell and bearing system. This hubset is purpose-built for our top-level NSW wheels and is now available separately. The ZR1 SL comes with carbon steel bearings with an aftermarket option for ceramic bearings for lighter weight. The hub's design creates a quick engagement feel, with 66 points of engagement. The six pawls are offset to work in two groups of three pawls. At any time, there are always three pawls engaging. That means the power from your legs quickly transfers to your wheels. The driver body's design keeps the pawls in place for disassembly to make service convenient. Zipp hubs utilize J-bend spokes, the most popular type of spokes today. J-Bend spokes, widely available, are easier to replace. ZR1 hubs are approved for use with light-assist electric bikes for road or gravel if the motor's torque does not exceed 60 Nm. Specifications Orientation: Front, Rear Axle type: TA 12x100, TA 12x142 Spoke holes: 24, 28 Brake compatibility: Disc (Centre Lock) Driver body type: SRAM XDR, SRAM/Shimano Road Colour (hub): Black Axle material: Aluminium front & rear Driver body material: Aluminium Bearings: Ceramic Power measurement: Not Compatible