With longevity 3-4 times longer than steel bearings, the ceramic ball bearings used in the SRAM 10/11-Speed Coated Oversized Pulley Wheel System (OPWS) from CeramicSpeed offers the lowest friction, fastest spinning pulley wheels available. The OPWS system is made from high quality materials with 17-tooth aluminum pulley wheels mounted with high quality CeramicSpeed bearings. CeramicSpeed bearings reduce friction and improve power transfer while saving you 2-4 watts. The bearings are treated with a super-thin (2 micron) protective coating to further reduce friction and corrosion or damage from foreign objects, while extending the durability and longevity of the product. CeramicSpeed bearings are handmade in Denmark to the highest quality standards for longer life and superior performance. Their ceramic balls are rounder, harder, smoother, stiffer, lighter and more durable than any other steel or ceramic balls on the market. Pro Teams and professional athletes agree, CeramicSpeed offers the very best high-performance pulley wheels for training and racing. The CeramicSpeed Coated Oversized Pulley Wheel System for SRAM 10/11-Speeds will have you yelling, "On Your Left!" on every ride.