i just priced a disc (front only) conversion for my road bike's carbon rimmed front wheel. new hub, spokes, fork, rotor, hydraulic XT lever and caliper is about 350 and the better part of a pound. just so there were be no surprises, i'm only considering this is after testing out a FS Ibis Ripley with XT brakes for a day on some tough, dusty singletrack and fire roads. the brakes were fine, zero noise, zero grab, and very smooth in actuation.