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Shimano Dura-Ace 9170 Di2 is here and we've ridden it (Image credit: Matthew Allen / Immediate Media)

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.

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.)

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.

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.