Now entering its second generation, Shimano's Dura-Ace Di2 Rear Derailleur is slimmer, lighter and tougher than ever.
Gone is the reliance on cable tension, indexing and a spring to control rear derailleur shifts, the Dura-Ace 9070 Di2 Rear Derailleur uses a worm drive to eliminate the pull and pull-back associated with a derailleur spring and cable. Once properly set up, the digital derailleur shifts with ultimate precision every time.
Smaller motors have allowed Shimano to dramatically reduce the unit's size and thus weight, and simpler E-Tube wiring cleans up the look. On the outside, the RD-9070's outer materials are virtually identical to the standard 9000 series mechanical unit. A carbon pulley plate shaves a few extra grams, and the WideLink parallelogram provides plenty of stiffness to ensure shifting accuracy.
In the event of a crash, a saver function allows the derailleur to move in towards the wheel and away from the force of impact. Then it automatically resets itself with the push of a button and a few gear changes. If the auto reset fails, a manual reset is possible via buttons on the battery harness module near the stem and handlebar junction that work much like a barrel adjuster for fine tuning.
The RD-9070 is available in a short cage version only and is compatible with Shimano 11-speed cassettes with a max cog size of 28t. Sold as derailleur only with no cables. 217g.
Note: The RD-6770 is not compatible with 7970 Dura-Ace Di2 shifters or wire kits. Reviews
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I like this but is capped at using a 28t cassette. The new 9170 can go to a 30t if you have plenty of hills to contend with and don't want to run an Ultegra di2 with a longer cage.
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