Shimano's Ultegra Di2 RD 6870 Rear Derailleur features much of the same level of performance as the Dura Ace group without the podium topping price tag. Taking its cue from the Dura Ace 9070, the profile of the 6870 has been trimmed, making it leaner than the previous Ultegra Di2 rear mech. The 6870 Di2 rear now also has 11 speed shifting capability with sleeker, more professional looking wiring and a mid cage version that can accommodate a 32t cog in the rear. Shimano's electronic shifting features E Tube technology, which allows you to customize shifting speed and even program how many gears the rear derailleur shifts through when holding the shift button down. Finally, the 6870 rear derailleur has built in crash protection. In the event of an accident, the rear mechanism will actually compress and tuck away.