Ceramic Speed has the most advanced bicycle ceramic bearing upgrades available and their Shimano 11s Alloy Pulley Wheels are a no-compromise option when it comes to ensuring every watt goes right into the road. Designed to work with both Shimano road and mountain derailleurs the pulleys are shaped to minimize friction and keep an ideal chain path. This optimization is necessary to reap the most benefits from their Grade 3 Silicon Nitride ball bearings that provide the maximum possible roundness and highest quality surface finish. That means a 15 increase in hardness and a 100 increase in smoothness over other ceramic bearings on the market resulting in lowering operating temperatures for less corrosion less wear and less friction so these pulleys not only go faster but last 3 – 5 times as long as standard bearings as well.