Features - Shimano DURA ACE Di2 RD-R9250 12-speed Shadow Rear Derailleur FULLY CUSTOMISABLE The drive can be adapted to the rider's preferences via the E-TUBE app Among other things, the shift speed can be set, a fully or semi-synchronous shift mode can be selected and the programme buttons on the gear lever can be assigned specific functions WHEN EVERY SECOND COUNTS Our exclusive wireless protocol increases shifting speed without sacrificing any of the shifting precision and reliability SHIMANO is known for Fast, jerk-free shifting for responsive acceleration at any speed Low profile rear derailleur design SHIMANO SHADOW RD Race endurance for less damage in crush Maintains compact and smooth appearance Product features Use: Road Group: Dura Ace Di2 R9250 Model: RD-R9250 Mount type: Direct Mount Gear rear: 12-speed Compatible chain: CN-M9100 HG 12-speed Max. teeth large sprocket: 34T Min. teeth large sprocket: 28T Max. teeth small sprocket: 11T Min. teeth small sprocket: 11T Max. front difference: 16T Total capacity: 35T Compatible electric wire: EW-SD300 Firmware update by E-tube Project: Yes E-tube port (pcs): 1 E-tube connector (pcs): 0 Di2 Wireless-Chip: Yes