Heat buildup is the mortal enemy of disc brake systems, and Shimano has pulled out all the stops with the XTR SM-RT99 CenterLock Disc Rotor to keep the brake calipers cool. Its IceTech technology utilizes an aluminum core sandwiched between stainless steel braking tracks, resulting in a lighter rotor that sheds heat faster than standard all-steel rotors. Additionally, the wavy alloy inserts on the inside of the braking track serve as cooling fans to channel heat away instead of into the brake caliper. All this attention to heat dissipation boils down to more consistent braking power and more confidence on the trails than you'd have with non-IceTech rotors. Please note that the XTR SM-RT99 rotors are only compatible with CenterLock hubs, and they cannot be adapted to six-bolt hubs. If you need a Shimano IceTech rotor for six-bolt hubs, check out the SH-RT86 XT IceTech rotor.