I know more about this topic than I ever wanted to, having owned a '19 REWB and a '21 REWB at the same time. The earlier rotor will technically bolt on but the caliper is moved further away from centerline on the '21 so you'll have a bit of pad hanging off the edge. Obviously that's not a good way to have things...
Fwiw - the rotor and the knuckle(spindle) are all that's really any different between the 400mm and the 390mm setups.
Fwiw - the rotor and the knuckle(spindle) are all that's really any different between the 400mm and the 390mm setups.
