SHIMANO Dura-Ace Di2 RD-7970A 10-speed Rear Derailleur
Fast precise gear changing for top level riding and racing thanks to highly innovative digital technology. Like the 7900 mechanical derailleur, the 7970 has a new carbon fiber rear pulley cage and the new design is compatible with wider range cogsets, accommodating up to a 27 tooth cog. The differences are the fact that the unit is now driven by a servo motor instead of a cable and spring, so shifts are identical and precise every time as the computer control unit analyzes each shift.
The derailleur has a built-in mechanism that will allow the body to move inward under impact to reduce the potential for damage in the case of a crash. Cycling through the shifting a couple of times allows the shifter and rear derailleur to automatically re-synchronize.
Compatible with 11-27T cassette sprockets