Why Did Shimano Redesign the Arms on the RT-CL800?

To stop the noise. Standard rotors deform slightly as they heat, and on a long descent where braking is continuous rather than intermittent, that warping is what produces the ticking and rubbing riders complain about. Shimano's answer on the RT-CL800 was a more robust arm geometry that holds the rotor truer through heat cycles, paired with ICE TECHNOLOGIES FREEZA, a radiator fin design that pulls heat out of the braking surface. The result is a brake that feels the same at the bottom of a descent as it did at the top.

The CENTER LOCK spline mount makes installation quick and self-centering, no six bolts to torque in sequence. Choose 160mm for most gravel and road setups front and rear, 180mm when you want more heat capacity or run heavier loads, and 203mm for sustained steep descending or e-bike and tandem duty. All three are compatible with GRX BR-RX810 and BR-RX820 calipers and with Shimano hydraulic disc systems using center lock hubs. A lock ring is included.