The CeramicSpeed OSPW Aero ALPHA system for Shimano 9250/8150 derailleurs updates the fastest proven aero derailleur cage to include CeramicSpeed's patent pending ADR bearing protection and quiet performing ALPHA disc with composite tooth profile pulleys. Furthermore, a speed defying pinstripe graphic has been added for a splash of visual motion.Injection Molded Carbon Fiber reinforced PA Aero cage reduces aerodynamic drag on the rear derailleur by up to 60% and offers new levels of strength and durabilityAlpha disc pulleys are paired with a composite, narrow-wide tooth profile to help prevent debris from external objects getting stuckThe 13-tooth upper and 19-tooth lower Alpha pulley wheels feature ADR bearing protection that completely encloses the bearingsThis OSPW System has handbuilt CeramicSpeed coated bearings installed in each pulleyGrade 3 Silicon Nitride ball bearings are 400% smoother, 128% harder and 58% lighter than standard steel balls normally used in the bicycle industry4 customizable spring tension settings for optimal setupCompatible with Shimano Road Dura-Ace R9250 and Ultegra R8150 12-speed rear derailleursIt is not possible to add these pulleys to a previous generation OSPW Aero cageItem SpecificationsDefined ColorBlackDrivetrain Speeds12Fits BrandShimanoFits ModelDura-Ace R9250Fits ModelUltegra 8150Largest Cog34 CeramicSpeed OSPW Aero Alpha Pulley Wheel System for Shimano 9250 and 8150 Cage Assembly