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Electronic shifting wasn’t invented by Shimano, but it was the Japanese company that first nailed the concept with the original Dura-Ace Di2 7970 groupset in 2008. Since then, the world of high-end road bike transmissions has never been the same. The new Dura-Ace Di2 R9150 groupset benefits from two generations and almost a decade of refinement, and as good as the previous editions already were, this latest one somehow manages to improve upon the breed, while also adding the long-awaited hydraulic disc brake option (R9170). Upon first impression, Dura-Ace Di2 R9150 is pretty incredible — yet it could still be even better.
The continuing evolution of robotic shifting
In terms of fundamental shifting performance, Shimano hasn’t broken any new ground with the latest Dura-Ace Di2 R9150 groupset, and there are no major changes in how Di2 goes about its core functions. After all, it’s difficult to imagine how much improvement could be made over the previous generation.
Just like prior Dura-Ace Di2 drivetrains, rider commands at the shifter are carried out at the derailleurs with flawless precision, each and every time, and without fail (barring exceptions like setup issues, crash damage, etc.). Rear downshifts are impeccably smooth, and individual rear upshifts are just as lightning-quick and consistent as before. Likewise, shifting between the two chainrings continues to be the best in the industry, hands down.
Based on extensive experience with previous Di2 editions, this latest R9150 groupset should laugh off torrential deluges of water, pressure washing, and merciless mud and muck, too: in other words, a wholly obedient robot in the form of a bicycle transmission.
But real-life robots aren’t like Rosie, that affable and witty housecleaning tin can from the Jetsons. Similarly, while Di2 has always been nearly flawless from a functional perspective, it’s also been a little lacking in personality.
Touch and feel
Shimano’s biggest challenge in improving Dura-Ace Di2 has never been one of function, but rather user experience. From an interactive perspective, the buttons were lacking in feedback, and it wasn’t always as easy as it should have been to tell the buttons apart, especially while wearing full-fingered gloves or while riding on bumpy terrain.
Both of those quirks have been addressed with Dura-Ace Di2 R9150. The buttons now have more audible and tactile feedback when they’re pressed. There’s more of a differential texture than before, and they’re also longer, for better accessibility, from both the hoods and drops. The improvements are subtle rather than dramatic, but they’re still noticeable while riding — and most welcome. As is typical for Shimano road Di2 controls, the button throws are still ultra-short, and certainly shorter than either Campagnolo EPS or SRAM Red eTap. This is either a good or a bad thing, depending on rider preference.
Otherwise, it’s the new hydraulic brake-compatible levers that see the most radical upgrades. Shimano debuted its R785 Di2-compatible hydraulic levers in 2013, but withheld the “Dura-Ace” label because the company never felt they were totally up to the standards expected of the nameplate.
To that, I’d agree. The inexplicably long hoods often required a shorter stem than usual, they had an annoying tendency to rattle when riding on rough surfaces, and, frankly, the aesthetics weren’t quite right.
Despite the fact that a hydraulic brake lever requires more space than a cable-actuated lever, Shimano has done an impressive job of cramming all of the bits into nearly identical forms. You’d be hard-pressed to tell the two Dura-Ace Di2 R9170 lever versions apart now, and they’re undeniably elegant to behold. Shimano anticipates that its pro riders will switch between hydraulic disc brakes and cable actuated rim brakes throughout the season, and two days of riding in Calpe, Spain, confirmed that there’s almost no way for your hands to discern between them.
In either case, the body length has also been restored to more typical dimensions, and the nicely rounded, compact shape is comfortable to hold with a little extra security coming from the newly textured hoods.
Both versions also offer a generous 41mm of brake lever reach adjustment, in addition to “Free Stroke” adjustment on the hydraulic version — which adjusts how much the lever travels before the brake-caliper pistons begin to move.
More customization is provided by a few new remote shifter options, too. A split configuration (similar to the carryover sprinter remotes) means the new climbing buttons are more compact than before, easier to actuate, and with more flexibility in where they’re placed. The even-tinier sprint shifters are carried over from Dura-Ace 9070, but sadly, they still only work with the cable-actuated Di2 levers, despite the hydraulic levers now sporting an additional e-Tube wiring port per side as compared to R785.
Shimano has overhauled its associated Di2 app as well, which now offers even more tuning options to help the system better suit your individual wants and needs. It’s also — finally — now wireless-enabled via Bluetooth, and works with iOS and Android mobile devices and Apple notebooks, in addition to the Windows-based computers it required before.
The array of tuning parameters on tap is dizzying. Choose whichever buttons you’d like for front and rear upshifting and downshifting, for example, as well as how quickly (and how many) gears you get when holding down a button. The hidden buttons atop the lever peaks return, too, and provided the system is equipped with the optional D-fly wireless communication unit, can be used to control a variety of compatible computer heads, and even some head- and taillights. In a first for Di2, those upper buttons can even be programmed to serve as additional shift buttons.
Buttons galore, in other words — and just like a Burger King Whopper, you can have it your way.
A little more human, but a little more robotic, too
Borrowed from the company’s XTR Di2 mountain bike electronic groupset are the new semi-Synchro and full-Synchro shift modes. The former will automatically shift gears out back to compensate for changes up front with the aim of helping you maintain a smoother cadence; the latter turns the system into a fully sequential system that controls both derailleurs as needed simply based on whether you want an easier or harder ratio. The number of “correction” shifts and when they occur can be user-programmed, but either way, both of the new modes are intended to handle some of the functions riders would typically do themselves.
In either mode, shifts that require the chain to move over to the big ring are quite impressive. Both ends shift simultaneously, and given how well Shimano moves chains to larger-diameter chainrings and cogs, it’s a virtually seamless affair that’s barely noticeable from the saddle. In semi-Synchro mode, this means you can increase your speed without jarring your cadence; in full-Synchro, it lets you go to harder ratios without ever having to think about when a front shift is required.
However, shifts to easier gears in either Synchro mode that require dropping to the inner chainring are notably clumsier and slower. Instead of shifting both ends simultaneously, the system waits until the chain is fully engaged on the inner chainring before making the correction shifts in the rear — a comparatively slow process that disrupts your rhythm while climbing. In fairness to Shimano, this is an operation logic that’s surely rooted in preventing dropped chains, but one that many experienced riders won’t need.
Making matters worse is the fact that, unlike with XTR Di2, full-Synchro mode provides no audible warning when a front shift is about to take place, so you can’t even prepare yourself for the disruption before it happens (unless you keep a vigilant eye on the optional gearing display on a compatible computer head, which isn’t likely).
Perhaps I’ll grow accustomed to both modes’ quirks given more riding time, but at least for now, I’m not completely sold on either Synchro Shift mode. Thankfully, full manual mode is always available via a quick double tap on the junction box.
I have the power
Without any way of verifying the quality of the data that was produced over the two days of riding, I don’t have any objective way to evaluating the core functionality of Shimano’s new Dura-Ace power meter — that’ll have to wait until later.
For now, I can say that the design has a lot to offer. Both strain gage arrays on the dual-sided meter are fully and permanently sealed from the elements, and since they’re hardwired together, the entire system is powered by a single rechargeable battery that’s safely nestled away inside the spindle. Once the claimed 300 hours of recording time have expired, the proprietary charge cable attaches via a neat Apple MacBook-like magnetic interface, which further helps protect the system from water and debris as there’s no access hole required for a more traditional plug.
Typical functions, such as pairing and setting the zero offset, are intuitive to perform, and the physical design is compact and tidy. Both strain gage pods are sufficiently low-profile that they’ll clear chainstay-mounted brake calipers — at least, according to Shimano — and aside from the small electronics box housing the button, indicator LED, and charge port, there’s little visual evidence that you’re riding anything other than a standard Dura-Ace R9100 crankset.
Dura-Ace hydraulic disc brakes at last
The first rides on the new Dura-Ace disc brakes were exactly as I had anticipated: the same generous power and ultra-fine control as on the current R685/R785 setups, but with less weight owing to the new flat mount, Dura-Ace-specific caliper bodies. Braking was also pleasantly smooth and quiet — at least in the dry conditions in which I rode — although I suspect the usual squealing will be present in wet conditions.
Likewise, the routes our group took didn’t provide sufficient opportunity to get the rotors properly good and hot, although the new design supposedly runs 30°C cooler than the previous Freeza models with its larger and more aggressive cooling fins. That cooling aspect is particularly important since Shimano continues to use mineral oil in its hydraulic braking systems instead of DOT fluid, which usually has a higher boiling point when fresh. However, DOT fluids tend to absorb atmospheric moisture over time — which lowers the vaporization temperature — and mineral oil isn’t nearly as toxic or caustic.
Given the rarity with which Shimano hydraulic brakes boil over, the decision seems well justified. Shimano still says dual 140mm rotors are suitable for road use — a testament to how confident the company is at the system’s heat management — but a 160mm rotor is now recommended up front for extra stopping power. Such a staggered arrangement is typical for other wheeled vehicles with disc brakes, so it’s a perfectly logical move.
Even disregarding the additional cooling capabilities of the new rotors, there are some key safety benefits of the new shape, too. Those cooling fins also make it nearly impossible to get a finger jammed in there, and the edges are much less sharp than before thanks to their rounded edges. All of those features that should go a long way toward tempering some of the injury concerns of pro riders.
I remain frustrated by the limited tuning options here, though. While the range of lever reach is generous, the range of Free Stroke adjustment is anything but, and regardless of which settings I chose, the lever always traveled further than I would ideally prefer before the pistons engage.
For whatever reason, Shimano has increased the brake-lever effort slightly as well, in contrast with its usual “Light Action” design philosophy. It’s hardly overbearing, and while I didn’t miss the intermittent rattling of the current R785 Di2 levers, I did miss their notably light and snappy feel.
The wheels on the bus go ’round and ’round
I was only able to sample one of the new Dura-Ace wheelsets during my test sessions — the 60mm-deep, rim-brake-compatible carbon tubulars — so I’ll have to reserve final judgment on these until later as well. That said, I couldn’t help but notice that they were more prone to crosswinds than other top-end aero wheelsets of similar dimensions that I’ve ridden recently, and braking performance wasn’t as good as some more advanced designs. And while I continue to be a fan of Shimano’s highly refined cup-and-cone bearing designs, I do wish the company would increase the number of teeth inside the drive ratchet so the chain re-engages more quickly when you start pedaling after coasting for a bit.
Stay tuned for more here either way.
Always room for improvement
I attended the first Shimano Dura-Ace Di2 launch in Suzuka, Japan almost nine years ago, and I keenly remember ripping around the Formula 1 track that day in the pouring rain, trying my damnedest (to no avail) to outsmart the system. I marveled at Shimano’s achievement then just as I do now, but even with all the incremental improvements made over two successive generations, I can’t help but see the unrealized potential of a concept that has so much to offer.
This may come across as a more philosophical point of view, but I might argue that the new Di2 is still a little too robotic in the way it coldly goes about its business. XTR Di2 gave me much hope for how this latest Dura-Ace Di2 groupset would feel, but I remain a little disappointed. The button action on those shifters is still extremely light, but the clicks are louder and firmer, and the longer lever travel — while still short — give even more of a signal to your fingers that you’ve done what you wanted. To me, the XTR Di2 interface represents the best available hybrid in terms of the feedback you get from a mechanical drivetrain with the robotic perfection you get from an electronic one.
Contrast that with this latest Dura-Ace Di2.
Even with the changes, the button action on Dura-Ace Di2 is the exact opposite of XTR Di2: a much shorter lever throw, a lighter and quieter click, and a firmer spring tension. Might Shimano’s engineers argue that road riders want a different kind of feedback than mountain bikers? Perhaps, but throughout my two days in Spain, I found myself constantly wishing for the XTR Di2 guts to somehow, magically find their way into the levers I was using at the time.
There’s also the issue of multiple gear shifts.
Even at the fastest setting, Dura-Ace Di2’s carryover Multi-Shift function forces you to hold down the button and wait until the chain has landed on the cog you want — and there’s a learning curve involved before your brain begins to intuitively know how long you need to hold that button to get the desired number of shifts. Alternatively, you can just tap the button four separate times (and with good, but still not great, tactile feedback to reward each push).
Meanwhile, XTR Di2 uses two-stage buttons: push to the first click for a single gear, or keep pushing to the second detent for two. It’s just boom, boom: two quick jabs of your thumb, and you’ve got four gears in either direction, far faster than any method currently offered with Dura-Ace Di2 (or Campagnolo EPS or SRAM eTap, for that matter).
There’s no ignoring the fact, either, that the complete Dura-Ace Di2 transmission comprises an awful lot of separate pieces. Shimano isn’t likely to switch to a wireless design any time soon, as a wired system offers some inherent advantages such as single-battery operation and reduced chance of system failure; it just goes against the company DNA. But as any seasoned road mechanic will attest, doing a proper pro-level installation on a Di2 drivetrain is highly time consuming — a fact further emphasized by SRAM’s ultra-simple Red eTap wireless groupset.
The new handlebar plug junction box, Y-format e-Tube wires, and associated Di2-specific cockpit components do make for a potentially cleaner-looking setup with wires running inside handlebars (and stems, depending on the frame used) and the long-overdue omission of that old and unsightly stem-mounted junction box. The updated D-fly module that Shimano introduced a few months ago is small and easy to incorporate into the system, too.
But why do we still have to use a separate junction box and wireless unit at all? Given the deep well of engineering talent at Shimano’s disposal, why can’t those functions be integrated directly into the lever bodies themselves? Peel back the hood on the hydraulic levers — the one that should have the least amount of room to spare — and there seems to be sufficient volume to add in a little more electronic hardware.
And I’m sorry, Shimano, but those new remote switches are far bigger and clunkier-looking than I would have expected. If the request from your teams was to provide a smaller solution for shifting from the tops, I’d say this one misses the mark by a wide margin. Expect to see lots of these pods glued (or taped) directly to the bars without the poorly designed rubber bases meant to go with them.
Perfect in some ways, but not in others
I’ve only ridden the new Dura-Ace Di2 R9150 groupset for two days, but my head already loves it so because of how relentlessly perfectly it moves the chain back and forth. But there’s something missing, something lacking, something just not quite satisfying enough for my heart to get on board as well. I want to interact with the machines in my life on a more visceral level, not just have them do my bidding.
Put another way, I know a dual-clutch automatic transmission in a modern automobile is faster and easier, but I get more joy from a standard manual.
In Japanese culture, the term “wabi-sabi” refers to something that is perfect not due to the absence of flaws, but because of them: that old antique table with that just-right patina of wear, the inclusions that give a yellow diamond that sought-after glint in sunlight, the way your favorite bottled water tastes because there’s just the right mix of stuff other than water interspersed between the molecules of H2O.
The engineer in me can easily see the marvel that is this latest Dura-Ace Di2, but the other side of my brain can’t help but wonder if the end product as a whole might benefit from a slightly more fuzzy logic.
No doubt, Shimano’s robot performs its duties better than it ever has — but maybe it could be a little more human while doing it.