While Shimano has offered electronic drivetrains on road bikes for five years, it's never been available for mountain bikes – until now. And, arguably, mountain bike riders need it more, because having to adjust grip on the bars to lever off a series of shifts while simultaneously plowing through a rock garden is downright scary. The XTR M9050 Di2 system means the softest thumb motion, rather than the heavy push mechanical systems demand, will now actuate small motors to move the chain. The transformation is akin to what dual-clutch trannies have brought to state-of-the art Audis and Ferraris.

A subtler improvement, is the ability to shift sans stalling your pedal stroke because the drivetrain senses load and "knows" precisely when you're putting the least tension on the chain. And in case you catch epic air, you can even shift on the fly–literally. 

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For riders who want to geek out, custom-programming the drivetrain to read certain "keystrokes" like a longer hold of the thumb lever, is now possible as well. Add a sprint mode for the biggest gear combo; or a climb mode that does just the opposite. And racers could pre-ride a course and dial in several pre-set shift patterns tailored to ten different track sections.

The introduction of 11-speed gearing for the rear as well as 11x1 drivetrains (11 x 2/3 will also be sold) is significant. Shimano's main rival, SRAM, has already had 11-speed for a few years. Speaking of SRAM, it's also chasing an electric drivetrain–which is great news, because it means that competition will surely force costs lower. Speaking of which, Shimano won't announce the price of XTR M9050 Di2 until closer to launch, which is Q4 of 2014, but expect a fairly significant bump above present top-line XTR. More at www.ridextr.com