Upgrade your Shimano rear derailleur with CeramicSpeed Pulley Wheels for reduced friction and extended lifetime. The pulley wheels are the fastest spinning bearings on your bike, making an upgrade to CeramicSpeed an effective way to save energy. CeramicSpeed Pulley Wheels can be used for all cycling disciplines, and will last longer than any standard pulley wheels. The CeramicSpeed Pulley Wheels for Shimano rear derailleurs are specially designed to reduce friction to an absolute minimum, virtually eliminating the drag associated with standard pulley wheels.