text: Shimano XTR Di2 M9050 transmission review | Cyclingnews
  By James Huang/BikeRadar 22 October 2015
  Shimano genuinely raised the bar with its new XTR Di2 electronic mountain bike drivetrain. Even its outstanding performance can't fully justify its exorbitant cost, though (Image credit: James Huang/BikeRadar)
  Shimano has done an incredibly good job of neatly integrating the motor into the XTR Di2 rear derailleur. You'd best protect it at all costs, however, because it'll cost a fortune to replace it (Image credit: James Huang/BikeRadar)
  The XTR Di2 'Firebolt' shifters use a rotary motion instead of Shimano's usual pivoting arrangement. The textured pads provide a surprising amount of grip for your thumbs (Image credit: James Huang/BikeRadar)
  Shimano will offer XTR Di2 in 1x, 2x, and even 3x chainring configurations. Regardless, the entire system can be controlled with just a single shifter if you want to with a clever Syncro Shift sequential shifting mode (Image credit: James Huang/BikeRadar)
  Both paddles are independently adjustable to fine tune the fit. Even so, none of our three testers ever grew completely comfortable with the design (Image credit: James Huang/BikeRadar)
  Clever ends on the wire attachment points for the shifters allow you to either feed the wires straight out or folded backward if you're using bars with internal routing (Image credit: James Huang/BikeRadar)
  The new XTR chain features flush pins and circumferentially riveted heads to help hold everything together under extreme loads (Image credit: James Huang/BikeRadar)
  Battery life simply isn't a major concern with XTR Di2. Most users will need to recharge the system only two or three times per season (Image credit: James Huang/BikeRadar)
  There were no arguments among BikeRadar testers that XTR Di2 worked exceptionally well. The question was whether it was remotely worth the exorbitant price premium over mechanical counterparts (Image credit: James Huang/BikeRadar)
  The best feature of XTR Di2 is the ultra-slick Syncro Shift mode, which allows a single shifter to seamlessly control both the front and rear derailleur. More to the point, it works so well that it makes two-chainring drivetrains relevant again for competition (Image credit: James Huang/BikeRadar)
  The front derailleur is shockingly light considering the power of the motor hidden within. It's not completely infallible, though, as the chain dropped to the inside a few times during testing despite what was deemed to be a perfect setup (Image credit: James Huang/BikeRadar)
  The 2x drivetrain largely negates the limitations of the relatively narrow XTR cassette range. That said, it'd still be nice to see a bigger spread here (Image credit: James Huang/BikeRadar)
  The rotary shifter looks and feels slick but none of us ever quite got on with its ergonomics (Image credit: James Huang/BikeRadar)
  The display is highly visible even in bright sunlight. There's a lot of useful information at hand, too, including current gear, battery life, shift mode, and even suspension mode if you're connected to a compatible Fox iCTD shock or fork (Image credit: James Huang/BikeRadar)
  All of the BikeRadar testers who have used XTR Di2 would have preferred a shifter paddle layout that was more analogous to the standard XTR paddles (Image credit: James Huang/BikeRadar)
  Sadly, you can't configure a left-hand shifter to operate the connected Fox iCTD suspension components (Image credit: James Huang/BikeRadar)
  On the bottom of the display unit is a small button to change the shift mode (Image credit: James Huang/BikeRadar)
  On the backside of the display unit are three e-tube wire ports plus a charge port (Image credit: James Huang/BikeRadar)
  The display unit shows you your current gear selection (and suspension mode depending on what components are attached). Also included on the display is battery life and shift mode (Image credit: James Huang/BikeRadar)
  Smatterings of carbon help keep the rear derailleur down to a reasonable 290g (Image credit: James Huang/BikeRadar)
  The toggle for the pulley cage clutch is very easier to operate (Image credit: James Huang/BikeRadar)
  Pulley clutch tension is adjustable through an external port. Previous versions required you to undo several tiny screws and remove a plastic cover (Image credit: James Huang/BikeRadar)
  Shimano has switched to set screws to adjust the low and high limits for the XTR Di2 rear derailleur (Image credit: James Huang/BikeRadar)
  Shimano has clearly gone to great lengths to boost the stiffness of the XTR Di2 rear derailleur. The parallelogram plates are big and stout, and the pivots are spaced far apart (Image credit: James Huang/BikeRadar)
  Dual return springs promise snappy shifts to smaller cogs (Image credit: James Huang/BikeRadar)
  Likewise, the motor is neatly integrated into the design of the front derailleur, which is surprisingly light (Image credit: James Huang/BikeRadar)
  Although the big bulge atop the front derailleur is hard to miss, the profile is admirably low (Image credit: James Huang/BikeRadar)
  There's just a single front derailleur; different brackets are bolted on to accommodate the various frame attachment methods currently available (Image credit: James Huang/BikeRadar)
  Shimano currently offers four different adapter brackets for front derailleur: high and low-clamp, and high and low direct mount (Image credit: James Huang/BikeRadar)
  The new 11-speed cassette is Shimano's biggest yet with an 11-to-40-tooth spread. Still, it doesn't offer the range of SRAM's XX1 cluster (Image credit: James Huang/BikeRadar)
  For the bigger cogs, titanium rings are attached with stainless steel rivets to carbon composite spiders, which in turn have co-molded aluminum centers to precisely mate to the freehub body. The middle cogs are attached to aluminum carriers while the smallest cogs are made from forged steel (Image credit: James Huang/BikeRadar)
  How does Shimano cram 11 cogs on to a 10-speed freehub body? By taking advantage of the spoke angles on the driveside and cantilevering the biggest cog over the spoke flange (Image credit: James Huang/BikeRadar)
  Not many frames are designed to hold a Shimano Di2 internal battery but that's likely to change moving forward. Pivot's excellent Mach 429 SL is one notable exception as it was designed around Di2 right from the get-go (Image credit: James Huang/BikeRadar)
  Few things have shaken things up in the mountain bike component world lately more than Shimano's groundbreaking XTR Di2 M9050 electronic group. After years of experience with motor-driven transmissions on the road side, one would expect that the XTR version would knock it out of the park on the first swing – but does it?
  Highs: Nearly infallible shifting performance, slick syncro shift sequential shifter mode, excellent shift paddle feedback, minimal weight penalty, lots of customisation options, excellent battery life, undeniably cool
  Upon the groupset's introduction back last October, Shimano essentially promised to do for the mountain bike world what the original Dura-Ace Di2 group did for roadies more than seven years ago: deliver absolutely perfect shifting performance regardless of conditions and with essentially no maintenance required whatsoever (aside from occasionally charging the battery).
  After plenty of initial backlash and skepticism, Di2 is now more than accepted on the road; in fact, nearly everyone who's ever used both standard and electronic transmissions will admit that the latter just flat-out works better.
  Perhaps it's not surprising then that our collective experience with XTR Di2 has been virtually identical, with shift performance that's nearly flawless – push the shift paddle and you get the same perfect chain movement each and every time, even when the system is horribly caked in thick UK mud or utterly soaked after a freak high Alpine thunderstorm. It's incredibly precise in its movements, more so than any mechanical transmission we've used.
  Not only is the system freakishly consistent in its operation but it's also uncannily smooth and fast with none of the clunkiness that can occasionally accompany even the most seasoned rider when a shift is executed at a less-than-opportune moment. We've all been taught to let up on pedal pressure when shifting but that's really not necessary with XTR Di2. The system knows just the right place in the cassette or chainring rotation to move the chain, and it does so with ruthless precision – front or rear – even when mashing out of the saddle uphill.
  For our 2x11 test drivetrains, we had the system hold on to the outer chainring as long as possible, only dropping down into the inner chainring for the lowest two gear combinations. An audible beep alerts you when a double shift (as in, both the front and rear at the same time) is imminent but in practice, it's hardly necessary. Shimano's best-in-class front shifting performance makes even double shifts feel eerily seamless from the rider's point of view.
  While Syncro Shift is certainly neat from a technological standpoint, its implications for drivetrain progression are more significant. Single-chainring drivetrains have quickly taken hold in recent years for good reason: they're easier to operate, they free up space on the bar, and they generally offer much better chain retention than multiple-chainring drivetrains. Even so, their narrower total gear range generally limits their appeal to fitter and faster riders.
  With Syncro Shift, two-chainring drivetrains are suddenly relevant again. With a Syncro Shift-enabled XTR Di2 transmission, you can get most of the benefits of a 1x system but with more range and smaller steps in between gears – even though the XTR's 11-40t cassette has substantially less spread than what SRAM offers. As with a 1x system, here's still no extra brainpower required to manage the multiple chainrings and the single shifter leaves plenty of room for dropper seatpost remotes on the other side of the bar.
  Chain retention isn't inherently as good, mind you, but good 2x chain guides already exist for those in need (and they seem to do the trick just fine for recent Enduro World Series champion Tracy Mosely's Trek Remedy 29).
  Moreover, Shimano has done road-going Di2 one better in terms of lever feedback. Many users – myself included – have long criticised Shimano for designing almost no feedback into Di2's shift buttons. Sure, it works, but the 'click' is disappointingly vague and the action arguably too light. Not so with XTR Di2, whose shifter buttons return a satisfying audible and tangible detent that reassuringly indicates you've requested a shift.
  The XTR Di2 rotary-style shifter also simulates Shimano's excellent Multi Release feature with two-stage buttons – push a little to change one gear; a little more for two. In fact, I found it much faster (and more predictable) to push the button twice than to hold it down.
  Few situations highlighted XTR Di2's outstanding performance during our test sessions than the Breck Epic, a six-day mountain bike stage race held in Colorado with roughly 35,000ft of climbing (and descending!) over 200 miles, all more than 10,000ft above sea level and oftentimes far out in the wilderness with no chance of a cell signal (and similar chances of finding XTR Di2 spares).
  Perhaps the best thing I could say about the groupset during that ordeal was that its performance was utterly consistent all week despite be doing absolutely no maintenance aside from re-oiling the chain each day and one quick post-stage rinse after getting hit with a nasty midday hailstorm. I topped off the battery after day one but didn't plug it in again for the rest of the event and finished with three out of five bars still showing on the handlebar-mounted LCD display.
  Keep in mind, too, that that's with a worst-case scenario that included ludicrously long climbs with hundreds of double shifts (shifting up front requires much more power than out back) plus electronically controlled Fox iCTD suspension components at both ends running off of the same battery pack. Just as road-going Di2 has proven over the years, battery life simply isn't an issue here.
  Across the pond, the biggest challenge was typical UK mud but even that couldn't get the system to hiccup. Even when the drivetrain was woefully heaped in slop,the powerful derailleur motors just kept on keeping on.
  Although the button feedback was a refreshing change from road-going Di2 levers, all three BikeRadar testers universally lambasted the rotary-style lever layout that Shimano has proudly touted as being more ergonomic than even its own mechanical shifters. It's nice that the paddles themselves are adjustable laterally but even so, the layout still never felt as intuitive to use as standard Shimano Rapid Fire. For example, even after living and breathing Di2 for six days at the Breck Epic (and after riding the system for nearly the entire summer), I still occasionally tapped the wrong button.
  Sharp-eyed readers will also notice that we characterised the shifting performance as mostly perfect. Despite careful setup (that included supervision and inspection by a Shimano representative), I still dropped the chain to the inside of the crankset four times during the Breck Epic, always when shifting down from the big-big combination while climbing under load. Granted, this is not an ideal situation but nevertheless, it's one that XTR Di2 is designed to handle (and is programmed by default to do in Syncro Shift mode).
  Making matters worse was the fact that you can't manually move the front derailleur cage over to re-engage the chain like you could with a mechanical transmission. I had to dismount and wrestle the chain back on to the chainring by hand, each time watching other riders pedal by in the process and occasionally waiting a pretty long time before there was a gap in the long line of marching ants before I could squeeze back in.
  The standard XTR transmission also holds an edge over Di2 in terms of weight, although it's a pretty minor difference all things considered – just 84g even after factoring in the additional battery and display unit that the mechanical version doesn't require. That gap draws even narrower, too, when you consider that Di2's e-tube wiring setup weighs less than steel cables and housing.
  Putting it into even more perspective is the cost of replacement components. Although road crashes tend to be more damaging per incident (blacktop is horribly unforgiving after all), crashes on the trail are certainly more frequent and there's also a far greater chance of drivetrain damage from debris. For the price of a replacement XTR Di2 rear derailleur alone, you could buy not one, but two complete Shimano Deore XT 2x11 drivetrains (including the shifters, derailleurs, crankset, chain, and cassette) – and still have money left over for beer.
  For sure, XTR Di2 should cost more than the standard XTR bits but even Shimano's own Di2 road groups don't carry as big a cost penalty compared with their mechanical counterparts. By any measure, XTR Di2 is insanely, ridiculously pricey.
  Therein lies the biggest question surrounding Shimano's groundbreaking XTR Di2 transmission. Sure, the performance it offers is second to none but is that enough to justify its cost?
  As much as we like the two-chainring configuration (at least in Syncro Shift mode) for its wider range as compared to even the best conventional 1x systems, there are still plenty of folks who aren't willing to go back to multiple chainrings – and with an oncoming flood of expanded-range 1x-specific cassettes, the reasons are even less compelling assuming you're okay with pretty big ratio jumps in between gears.
  Tom Marvin, technical editor for BikeRadar's sister print publication, What Mountain Bike, perhaps sums up the quandary best.
  "'I think Syncro Shift is what makes the group work as a whole. If you want the top end of performance race/marathon components, I think Di2 does deliver that," he says.
  "'But I don't think Di2 is particularly relevant for 99.9 percent of riders in its current format, and I'd probably not recommend it to many people. If all you want is a 1x trail groupset, you're better off with something else. I think it really is equivalent to a track-car – ace to have if you can afford it and don't particularly need to justify it to the other half. You have it because it's nice to have. The question is, is there anything wrong with that?"