If you ride a bike, you probably have a general idea of how gears work. You push the lever, a steel wire tightens, and the little springs in your derailleur cause the chain to shift onto a new cog with a satisfying thunk. Like many velo-enthusiasts, you probably find this process simple, clean, and classic. Well, nuts to you, luddite. Shimano is bringing the new electronic hotness, and it has tiny little motors.
Starting in 2009, competitive and/or rich cyclists will be able to shift using a fully motorized system, called Di2. Part of Shimano's top-of-the-line Dura-Ace component family, the new shift levers, derailleurs and battery will deliver lightning fast and accurate shifting performance. And at not too much more weight. The new system is 67 grams lighter than the current Dura-Ace 7800 and only 68 grams heavier than Dura-Ace 7900 series. That's pretty light. And since all the wires are closed (and don't move), they won't get gunked up on the road. Although presumably, the new system will slightly increase the water sensitivity.
The biggest challenge for systems like this is power- the batteries need to last long enough for epic rides, yet be super light. Shimano engineers claim the Di2 battery will last 1,000km between charges, and keeps the weight right smack between the 7800 and 7900 parts series. If true, that's pretty sweet.
I ride a fixie when I bomb around town, so electronic shifting magic doesn't hold a lot of immediate appeal. But I have been eyeing a higher-end road bike for more epic rides. There's no way on earth I could afford the Di2 unless I knock over a liquor store. Then again, I'll be able to make my escape a lot quicker on an electronic ride.