Designed to keep your braking system cool on long, demanding descents, the XTR RT-MT900 Centerlock Disc Rotor rapidly dissipates heat for more consistent braking performance in extreme conditions, as well as longer pad life and reduced brake fade. These rotors are optimized for the XTR M9100 and M9120 brakes, and feature a new design that improves cooling and decreases weight compared to the previous version of the XTR rotor, the RT-99. Employing Shimano's Ice Technologies Freeza construction, these rotors use a 3-layer design consisting of two steel braking surfaces sandwiched over an aluminum core. This allows Shimano to take advantage of the high thermal conductivity of aluminum, whereas most companies simply use steel rotors. And thanks to a new heat dissipating paint on the exposed parts of the aluminum layer, the RT-MT900 rotors see their surface temperature cooled by up to 20-degrees Celsius compared the previous XTR RT-99 rotors. The 140mm and 160mm sizes are optimized for XC and focused on weight reduction, whereas the 180mm and 203mm rotors are made for aggressive trail and enduro with an emphasis on efficient cooling.