Description Performance electronic shifting has finally become a reality with Shimano's Dura-Ace Di2 (Digital Integrated Intelligence) components. Gone is the reliance on cable tension, indexing and a spring to control rear derailleur shifts. The Dura-Ace 7970 Di2 Rear Derailleur uses a worm drive to eliminate the push and pull associated with a derailleur spring and cable. Once properly set up, the digital derailleur shifts with ultimate precision every time. Also, in the event of a crash there is a saver function that allows the derailler 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 the rider merely needing to run through the gears a few times. If the re-set fails, there is even a way to manually re-set it on the fly with buttons on the battery harness module near the stem and handlebar junction that work much like a barrel adjuster for fine tuning. Otherwise, any of the features of the 7900 mechanical Dura-Ace rear derailleur remain like a carbon pulley cage and P-body, titanium B axle, manual limit screws, and wide gear ratio of up to an 11-27 cassette. Includes rear derailleur only without wires.
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