With the fast and accurate Di2 shifting technology, the Shimano 12-speed Ultegra RD-R8150 rear derailleur is extremely versatile thanks to a single cage length option compatible with 11-28, 11-30, and 11-34 cassettes. FEATURES : Compact design includes an integrated wireless unit, charger, switch Wider range capacity Max. low sprocket 34t LED status indicator Battery indicator, pairing, adjust mode etc. SPECS : Largest Cog: 34 Rear Derailleur Mount Type: Shimano Rear Direct Mount , 10x1 Standard Chain Wrap Capacity (teeth): 39 Rear Der/Shifter Compatibility: Shimano Road Di2 Cage Length: Medium Drivetrain Speeds: 12