Shimano XTR Di2 is the Next Step in Mountain Bike Evolution
Since Shimano launched Dura-Ace Di2 six years ago, some riders, and companies such as K-Edge, have been hacking the road system for the trail. So it was obvious that eventually Shimano would produce a dedicated electronic drivetrain for dirt. XTR Di2 M9050 isn't just a modified road group, but also an 11-speed mountain bike drivetrain with features all its own—some of which even supersede what's available on the road.
It takes only one ride to realize how good it is. Removing the cables makes shifts faster, more accurate, and more consistent. It's impossible to push the lever halfway and not fully catch a shift—each touch is a complete and precise gear change. There's also multishift, in which the derailleur fires off consecutive shifts until the lever is released, dumping gears faster and more accurately than any mechanical system. This feature was less useful on the road, where speed and terrain changes are more gradual, but it's a leg-saver on dirt, where you're often surprised by a climb or obstacle.
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Rather than the button-like feel of road Di2 shifters, XTR Di2's Firebolt shifters feel similar to mechanical mountain levers, and I like that the levers are closer together than on mechanical systems. This is, however, the one feature of the group that could use some fine-tuning: I think many riders will prefer smaller shifters that operate off a shorter throw.
The front shift lever is optional here, thanks to a feature—specific to XTR Di2—called Syncro Shift, which automatically shifts in front. And it doesn't just perform a chainring shift—a split second later, it makes what Shimano calls a "recovery shift" in the rear, to reduce the ratio difference and disruption to your cadence. You can toggle between two customizable front shifting settings on the handlebar display (also an XTR Di2-only feature), as well as a manual mode that disables Syncro Shift.
Fox's iRD electronically activated suspension can be integrated into XTR Di2, and can run off the same battery. It provides simultaneous lockout on the shock and fork via a single switch mounted on the handlebar, and you can set the Di2 digital display to show whether the suspension is fully locked or open. The battery can run both iRD and Di2, using a double-chainring setup, up to five hours a day for seven days, with power to spare. Results will vary based on temperature, how many and what types of shifts you make, and the length of the wires, but I think these numbers are on the conservative side: I recharged only every two months, riding the Di2-equipped bike at least twice weekly.
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The system is incredibly customizable through Shimano's PC-compatible, E-Tube Project computer program. You can designate when Syncro Shift happens based on which cassette cog you're in and how many cogs you want it to jump in the rear recovery shift. Derailleur speed and individual shift-lever function can also be modified, so you can make the top lever upshift and the bottom downshift, like I did; or even have the left shifter operate the rear derailleur.
An 11-40-tooth cassette comes stock, so running a 1x configuration is limited to stronger riders on lighter bikes, unless you swap in Shimano's heavier but less expensive 11-42 XT cassette, which is compatible with XTR. System weight with the front shifter removed and in a double-chainring configuration is within a few grams of a mechanical XTR drivetrain. Cost, on the other hand, is as much as $1,290 more. This will keep a lot of riders off of XTR Di2 for now, so this technology won't have widespread impact until it's offered in a lower-cost version—say, XT Di2—if that ever happens. But history suggests that it will, similar to the way the trickle-down took place from Dura-Ace to Ultegra Di2. And although Di2 is a fairly mature technology, the future integration possibilities beyond electronic suspension are huge. Electronically activated dropper posts, GPS, power meters, and even lighting could all be integrated into the system.
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Despite the cool features, smooth operation, and tech advances, XTR Di2 is less a game changer than the next natural step in the incremental evolution of mountain bike drivetrains. It exists for the same reasons that cars moved away from cable-actuated gas pedals 15 or so years ago—more consistency, reliability, and system integration. You don't need it, but once you try it, you'll want it.
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