The world's fastest pulley system has become even faster. The OSPW Aero boasts a lifetime warranty and is wind tunnel tested to have 40% less friction than a standard derailleur, making it perfect for time trials or triathlons. The OSPW Aero is an industry-leading product, developed in collaboration with one of the world's leading aerodynamicists, Simon Smart, and is chosen by World Champions and top-level athletes worldwide. This OSPW system features hand-built CeramicSpeed bearings and its unique design and craftsmanship will win you over from the first use. The system features a 13-tooth upper pulley and a 19-tooth lower pulley to ensure absolute derailleur optimization, and the oversized aluminum upper and lower pulleys are mounted with coated CeramicSpeed bearings, refined through years of experience. The OSPW Aero for Shimano 9100 and 8000 has an integrated stop tab for easier installation. This is an updated version of the Oversized Pulley Wheel System for Shimano 9100/9150 and 8000 SS/8050 SS. Note: The OSPW Aero System for 9100/9150 and 8000 SS/8050 SS is NOT compatible with Ultegra 8000-GS or 8050-GS derailleurs (medium cage), nor with Ultegra RD RX800 & RX805 derailleurs with a clutch. For a version compatible with RX800 & RX805, see our OSPW X for Shimano RX800/805. For a compatible upgrade for Ultegra 8000-GS or 8050-GS, see our Pulleys for Shimano, 11s NW. Please note that, despite design similarities, this OSPW Aero is not compatible with 12-speed Shimano 9200 or 8100 series derailleurs. The Shimano 9100/8000 OSPW Aero system is compatible with cassettes up to 32 teeth for both Dura Ace and Ultegra derailleurs. In the box: Complete OSPW Aero System for Shimano 9100 and 8000. CeramicSpeed Pulley Bearing Oil, 15 ml dropper bottle.