We asked Harald Troost of Shimano Europe to talk us over the new Di-2 system, and here's what he said. The electronic system - which is about 50g heavier than the new mechanical Dura-Ace but lighter than last year's gear - runs from a downtube mounted battery and an inline controller that you can access from the bars. The feel of the system is super-light - we've only tried it on the turbo on the Shimano stand, not out on the road, but the levers only need the slightest nudge and the shifting is accurate and immediate. The biggest difference is at the front; it's very odd not needing to push hard to change to the big ring. It's the front mech that requires the most power and it's the first to die when you run the battery down. Shimano have designed the system to fail in quite a sensible way: first the red low battery light comes on, then some 250km later the front mech starts to slow. Eventually it'll stop altogether, but shifting at the rear - which doesn't require as much power - continues until the battery is dead. At that point you're stuck with whatever gear you chose last. Harald told us that in all the testing through the season so far with a number of pro teams, nobody's ever been in a position where the battery ran down, and to be honest unless you're routinely riding over 250km, or you're very forgetful, there shouldn't be a reason to run out of juice. Weatherproofing looks pretty good and the units have been tested in Europe through the winter, but time will tell on that front. There's obvious advantages in some sectors of the sport for having an electronic system, time trialling being the obvious one. You can have as many control buttons as you like: one on the flats or drops for when you start, one on the aero bars for when you're tucked. This was one of the reasons Mavic's electric system lasted much longer in TT circles than it did anywhere else. For the everyday rider there's less of an obvious advantage, okay the light front shifting is nice but it's not going to be reason enough to spend the extra.