Shimano XT RT-81 Ice-Tech CenterLock Disc Brake Rotor – 180mm. Take your stopping power to a whole new level with these sick new rotors. They use Ice-Technology to give you 25% more braking power. The 3-layer Ice-Tech rotor has an aluminum core between stainless steel for the ultimate combination of weight savings and heat radiation. These rotors run significantly cooler than the old all-steel rotors, providing more consistent braking power, less noise and longer pad life.