Recently in the shop we had the opportunity to build up the first Shimano Di2 bike for a customer. For anyone who is unfamiliar, Di2 is Shimano's new electronic shifting Dura Ace group (DA 7970). It uses wires connecting the shifters to the derailleurs and buttons on the shifters to actuate shifts. All of this is powered by a rechargeable battery mounted on the down tube right above the bottom bracket. Shimano claims that the electronic group provides superior shifting especially under torque and always makes sure the front derailleur is in the ideal position. This second part is undeniably true. The computer in the front derailleur auto trims, accompanied by a very Robocop type noise, to eliminate rub as you shift through the cassette. The design for the superior shifting comes from making  the computer slightly over shift before returning to its position holding the chain in gear.

On the bike we built the front shifting seemed to be noticeably improved from previous DA groups and fractionally better than the regular cable actuated 7900. As far as the rear shifting it seemed to be about on par with it's non-electronic sibling and did not provide the increased accuracy under load that Shimano had previously claimed. My other criticism of the shifters is the design of the buttons. Mostly they just don't move enough. It might be it is just what I am used to, but the lack of a positive click makes the shifting feel as computerized as it actually is. Maybe this is what the engineers were going for, but it leaves something to be desired in the satisfaction department. All and all, Di2 is pretty cool and very expensive. If you have the extra couple of thousand dollars to spend on an electronic shifting bike, maybe wait until the second generation rolls around. There will doubtless be improvements.