Shimano has been hard at work refining their highly reliable and successful Ultegra Di2 group. This latest 6870 version is 11-speed compatible as well as featuring lighter with a slimmer profile making it more like its flagship Dura-Ace big brother. It is offered in a SS version that works up to a 28T cog and a new GS version that works up to a 32T cog. The GS version can also be used with Dura-Ace 9070 Di2 to use a 32T cog with a Dura-Ace (there is no 9070 GS rear derailleur).The best thing about Ultegra Di2 is you get Dura-Ace Di2 performance at a fraction of the price.

Most derailleurs use a spring and cable tension to move the chain from cog to cog. The Shimano Ultegra RD-6870 Di2 rear derailleur employs highly innovative digital technology where an electronic signal is sent to a worm drive motor move the chain from gear to gear. Shifts are lightning-quick with no hesitation. Performance is on par with Dura-Ace Di2 except the Ultegra uses a slightly bulkier motor and has an alloy cage instead of carbon.

For those concerned with damaging the derailleur in a crash, Shimano's engineers included a servo-saving mechanism that allows the rear derailleur to handle a big side impact with minimal damage. Shifting is completely customizable. Shifting speed and the amount of cogs shifted with a press and hold can be tuned to each rider's preferences.... Read More