The XTR 2x10 drivetrain represents the top end of the mountain bike drivetrain world. It's the pinnacle which all other companies aspire to be more like- lightweight, functional, durable and fully race worthy. There's really nothing much not to like about such a coveted groupset that's run on the world's top end rigs. The disc rotors are meant to engage with the wheels with optimal stopping power. Shimano's Ice technology also assures that the system dissipates heat well and won't burn out on you.