This article originally appeared on BikeRadar
The disc version of Shimano's flagship Dura-Ace Di2 groupset has been in the pipeline for months, and we've finally taken it for a ride. Shimano debuted Dura-Ace electronic shifting in 2009 with its original Di2 7970 group, and added hydraulic road discs with its non-series R785 components years later, but R9170 is the first full-fledged Dura-Ace group with electronic shifting and hydraulic brakes.
While SRAM jumped straight into hydraulic discs with its top-level Red 22 group in 2013, Shimano opted to wait until the Japanese company was satisfied with the performance before bestowing the Dura-Ace moniker.
I tested the new groupset at Shimano's launch in Calpe, Spain.
Key features of Shimano Dura-Ace Di2 R9170
- Subtly refined digital shifting and ergonomics
- Optional 'synchronized shifting'
- Programmable buttons and shift speed
- Slimmed down hydraulic levers
- Optional integrated power meter
- Junction box can now be tucked inside handlebar end
Shifting performance – hard to fault
For my first 9170 experience I was sat on this thoroughly delightful S-Works Venge Disc (Sagan Limited Edition!), along with Shimano's latest C60 carbon tubular wheelset (28mm wide, and a claimed 1,480g for the set). The only thing this bike lacked was the new Dura-Ace power meter, which seems to be in rather short supply just now. (The power meters were originally supposed to be available for testing at the press camp, but they didn't arrive in time.)
As this is now the third generation of Dura-Ace Di2, it will come as no surprise that shifting is very, very good. The groupset tolerates all sorts of bad behaviour without complaint, for example running amazingly quietly even when fully cross-chained in big-big, a consequence no doubt of the work Shimano has put into improving performance with wider disc hubs and shorter chainstays. (Shimano specifies a minimum 410mm chainstay with 135mm rear spacing.)
Shifts are precise and rapid, and the buttons have a more positive click to them than previous iterations. It's not the rifle crack of SRAM eTap, but there's a useful extra bit of feedback with 9170 that makes it easier to feel what you're doing when, for example, you're wearing gloves.
Ergonomically things are very familiar to Shimano users, but what's really impressive is they way the lever bodies have shrunk down. The hydraulic/Di2 9170 hood is virtually the same size as 9000's rim brake Di2 hood, and it's also almost identical in volume to the new 9100 mechanical hood.
The one downside to this is that Shimano don't seem to have done much to improve the levers' adjustability. We haven't had a chance to fiddle with the mechanism properly yet, but it appears that the reach adjustment and (very limited) free stroke adjustment have been carried over from DA 9000/9070, so adjusting bite point still isn't particularly straightforward.
My test bike had the top buttons set to perform the genuinely useful function of cycling through the screens on a Garmin Edge 820 computer. Another appealing option for the top-button functionality: the ability to control a set of lights such as Bontrager's remote-controlled Transmitrs.
That synchro feeling – our robot overlords have arrived
Synchronized Shifting is one of the headline features of 9170, and it works on much the same principles as its mountain bike counterpart, XTR Di2. In ‘fully synchronized' mode, the rider only needs to operate one shifter (the righthand one, by default), issuing an 'up' or 'down' command, and the system decides when to shift the front derailleur. In ‘semi-synchronized' mode, the rider shifts normally, but front shifts are accompanied by an automated rear shift to smooth the transition, avoiding a sudden, large change in effort.
First impressions are that synchronized shifting works well enough in that it does what it promises and is largely idiot-proof, but I didn't actually like it very much in practice. The issue is that unless you are paying very close attention, you won't know which rear shift will be accompanied by a front shift. I'd liken it to driving a car with an automatic gearbox – a portion of your brain needs to be dedicated to anticipating the behaviour of the transmission to get the best out of it, and it's a distraction that I'd rather do without.
It's not that the front shifting is poor or anything – it's not. In fact, it's truly class-leading. The reality is, however, that you simply cannot disguise the act of pushing a chain off one chainring and onto another beyond a certain point. And I found that an unexpected drop to the inner ring whilst out of the saddle could be quite jarring because of the sudden, momentary reduction in resistance.
While it's fair to say that my brief experience hasn't totally sold me on the concept of synchro shifting, the huge customisability offered by 9170 is very impressive, and there is, of course, no obligation to make use of the synchro features - in 'manual' mode the shifting of front and rear derailleurs is entirely up to you. You can literally assign any shift action (FD up, RD down, etc.) to any of the buttons, even the hidden ones on top of the hoods, and if you are using synchro you can configure its behaviour via desktop PC, tablet or a smartphone.
The braking is as thoroughly competent as the shifting. It rained for much of my two initial rides and power and modulation didn't suffer at all. The brakes did make a bloody racket, but that's hardly unusual for discs in the wet, and they quieted down when things dried out slightly.
Early verdict: very good indeed, if not particularly surprising
First impressions of the new Dura-Ace Di2 are very positive overall. It's a cleanly executed design that builds on the success of Dura-Ace 9070, and Shimano fans will certainly be happy as long as they can cope with the new look. (I wasn't sure from pictures, but it's actually very handsome in the metal.)
It's a tremendously customisable groupset and the potential for screwing around with different button arrangements and tweaking the behaviour of synchro shifting will amuse the technically minded. It also offers a lot to riders with unusual needs – time trialists and triathletes who want whacky button configurations, physically impaired riders who want all their shifting taken care of by a single lever… the potential there is huge.
If there's one letdown, it's that Shimano hasn't really pushed the envelope here. Numerous subtle refinements and tweaks make for a more usable, versatile groupset, but the button arrangement is still fussier than SRAM eTap's for example, and the lever adjustments still aren't as convenient or useful as those found on mountain bike hydraulics.
Nevertheless, Dura-Ace 9170 looks the business and does the business. I don't know if Shimano has quite achieved perfection, but I'm looking forward to spending more time with the new groupset.