First Ride: Shimano XTR M9050 Di2

Shimano launches the world’s first production electronic mountain bike drivetrain

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A single Di2 front derailleur utilizes various modular mounts, which make it compatible with most frames. The cage automatically trims in and out with rear shifts to prevent chain rub. (Courtesy)
Shimano has officially unveiled an electronic Di2 version of its XTR group. It's the first-ever dirt-specific production electronic drivetrain, although other companies, including as K-Edge, had previously hacked Shimano’s Di2 road drivetrain for off-road use.

There are many benefits to electronic shifting. Its greatest attribute is the durability and consistency. Without cables to stretch, wear, or get contaminated, shifts are as precise and feel exactly the same on day 300 as day 1. On the road, I’ve been riding an Ultegra Di2 group for just over two seasons now and have only had to adjust the rear derailleur when I swap wheels with slightly different cassette spacing. The front derailleur? Never. Frozen cables are a thing of the past, too. The original battery pack is still going strong and taking full charges. Not once have I had a mechanical…or is that electrical?

Since the digital aspect of the system takes human error out of the shift, each one is precise and clean. There are no more cranky shifts when you push the lever only half way or slightly too far. And when you need to dump multiple gears, Di2 does so quickly but at a controlled rate so the chain has a chance to hit the ramps built into the cassette for a shift that’s as smooth and quick as possible.

The latest version of Di2 offers customization, speed, precision, and consistency that no drivetrain to date can match. “Mountain bikers don’t want just buttons and batteries—they want better performance,” says Shimano’s Matt Robertson. I got the chance to briefly ride a prototype XTR Di2-equipped bike and it does indeed do things mechanical groups can’t. Plus, it has a few features that wowed even this longtime Di2 road user.

The prototype Di2 group I rode was crude compared to the dialed-in production pieces but its function was impressive. (Ron Koch)

The System
The XTR M9050 Di2 group is fully compatible with Shimano’s recently introduced M9000 11-speed mechanical group. The Di2 system consists of two derailleurs, an internal or external battery, shifters, a handlebar display unit, and wires. The derailleurs contain custom servo motors that drive the derailleur when a shift button is pressed. The 289-gram rear derailleur features Shimano’s Shadow RD+ low-profile design with a one-way clutch. XTR Di2’s front derailleur is a claimed 25 percent more powerful than M9000 mechanical, which means better shifts under high loads. Trim is automatic—as the rear derailleur shifts, the front adjusts itself to prevent rub. The front derailleur comes in double- and triple-chainring versions and has modular mounts: high clamp, low clamp, D-type and E-type.

Learn more about Shimano’s Shadow RD+ technology.

The shift units, dubbed FIREBOLT, feature a customizable rotary design and are located roughly where the rider’s thumbs and index fingers naturally rest while holding the grips. Their stroke and click are artificial. A single click offers one shift. Hold the button down and the system will make multiple shifts in the given direction. A rider can use a traditional left and right shifter or just run one right-side shifter—even while running a front derailleur. Yes, you read that right: Shimano developed a mode called Syncro Shift that automatically shifts the front derailleur, eliminating the need for a front shift lever. When the derailleur reaches the top or bottom of the cassette, the system lets out an audible beep. Hit the rear shift button one more time and the computer simultaneously shifts to the other chainring while moving to a different gear in back (so that you’ve essentially jumped to the next hardest or easiest gear). You can use the front shifter to override the Syncro mode but Shimano says nearly all of its test riders took the front shifter off after a while.

Watch Shimano’s Syncro Shift in action.

The digital status display shows battery level, gear position, shift mode and iCD (electronically controlled Fox fork lockout) position. A Syncro shift mode switch changes settings between Syncro map 1, 2, and manual. There is also an adjustment mode with numerical indicator. The display unit contains the internal battery charge port as well as the computer interface.. The interface allows the user to modify switch functions as well as Syncro shift type and timing. Shimano says a rider could even use the left side shifter to function as a Fox iCD lockout switch.

The handlebar-mounted display unit provides data, a computer interface, and a port to charge an internal battery. (Courtesy)

Armchair critics will have a field day with electronic mountain bike shift systems. And they may have a few valid concerns. The battery is the same unit used on the road group—depending on how often you ride, it can last around six months. A single-chainring setup would obviously use less energy than a double or triple but the XTR Di2 rear derailleur has to overcome the one-way clutch mechanism, which requires a little more juice. When the battery dies you first lose the ability to shift the front derailleur, followed shortly by the rear. Then you’re stuck in whatever gear combo it died in because you can’t manually move the derailleurs. Technically, XTR Di2 is 47 grams heavier than the mechanical group, but wires are lighter than cables and housing, which makes the difference negligible. According to Shimano, the total system weight is the same as mechanical in the 2X configuration, using just the rear shifter in Syncro shift mode.

A small yet powerful motor drives the Di2 rear derailleur. A one-way clutch mechanism controls chain movement for better retention and less noise. (Courtesy)

The Di2 shifters feature short buttons conveniently located near the rider's fingers. (Courtesy)

The Ride
While I admit that the five-minute parking-lot session I did on prototype XTR Di2 isn’t much of a first ride, it revealed a lot. First, the shifter location is ideal and right near your fingers so you’re not really reaching for it. The feel is light but a distinct click lets you know you shifted. In Syncro mode, I was blown away by how well the system worked. With the triple chainring I was able to shift from the highest gear combo to the lowest just by holding the shift button down and pedaling. I even put a fairly heavy load on the drivetrain by dragging the brakes trying to bind things up, but the drivetrain never protested. Simply put, I was amazed. Ergonomics-wise, the ability to place buttons wherever they’re needed is a huge benefit over mechanical levers that not only come with bulky mechanisms but are also often constrained by the movement required to operate them correctly. Then there’s the programmable interface that lets the rider decide which button operates each feature. I’ll admit, the world doesn’t really need electronic shifting but once you try it I’d be shocked if you didn’t want it.

Electronic shifting opens the door to integration with other electronically operated components like Fox’s iCD suspension. It seems logical for more products from various manufacturers to follow in the coming years such as electronic dropper posts, shocks, and more forks. Pricing is not yet available but it’s likely to cost roughly 40 percent more than mechanical XTR (the difference between mechanical Dura Ace and Dura Ace Di2). You have time to save your cash—XTR M9050 Di2 won’t be available until late this year.

Front Derailleur (FD-M9050 D-type): 115 grams
Rear Derailleur (RD-M9050-GS):        289 grams
System display (SC-M9050):               30 grams
FIREBOLT shifter (SW-M9050):        64 grams

This external battery unit mounts to water bottle cage bosses. (Courtesy)
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