The CeramicSpeed Oversized Pulley Wheels System has been proven to be the fastest pulley system in the world, providing energy savings starting from 2. 4 watts over standard Shimano systems. The OSPW system for Shimano 9100/9150 and 8000 SS/8050 SS is an industry leading product, chosen by many of the world's leading cycling teams and professional competitors. Featuring a 13-tooth upper pulley wheel and a 19-tooth lower pulley wheel to provide absolute optimisation of the rear derailleur. The upper and lower oversized aluminium pulley wheels come fitted with either standard or coated CeramicSpeed Bearings.