Welcome to the cycling space age. Shimano's Di2 has taken one of the few traditional bits of the bicycle and slapped it about with some science.
While bike materials have changed dramatically in the last few years (carbon fibre and titanium, for example) and brakes have gone hydraulic, suspension types have multiplied and even tyres have gone tubeless, the good old-fashioned gears are pretty much as they've been since the 70s. Enter Shimano's electronic gear-shifting tech to change all that.
Servo motors are activated by a press on a brake lever gear-shift button. And the gear simply moves, albeit with an absolutely sweet mechanical growl that says ‘I spent more on my chainrings than you did on your bike’. In fact, that sound is probably the sexiest bit about Di2.
What you get alongside that growl, and the admittedly stratospheric price-tag, is essentially Shimano's top-of-the-range roadie gear system turned electronic. Perfect shifting every time – with absolute precision – is the result.
The onboard processor even adjusts minutely to take account of which gears you're currently in and to avoid any chain rub. The processor can also handle hurried multiple shifts on both front and rear simultaneously.
They're not faster than the fastest road gears, but they are much more accurate. And, importantly, they won't need adjustment over time. Even the battery goes for at least 2,000km between recharges. So it's unlikely to die on you mid-ride, unless your ride is round the world.
This is truly great tech, but there are downsides. First, of course, we were all getting on fairly fine without high-tech gear changes – there's nothing wrong with a tiny bit of finger effort and the occasional adjustment (that's why derailleur gears have lasted so long, after all). And, of course, if this stuff does break it's not going to be mended with you poking about with a couple of tools.
Plus, Di2 is actually a bit heavier than its mechanical top-of-the-range rivals (but only enough to worry those who're complete weight weenies). Finally, there's the price – it's incredibly, extravagantly expensive. But then having the future, here today, costs – as any early adopter can tell you.
Is the wow factor enough to make you overlook the price tag? That's your decision.