With Shimano Dura Ace Di2 offered the first electronic switch for racing bikes. Although still happens that shifting with the combined brake and shifting handles, but a current wire along or through the frame will bring the signal to the derailleur.
From the outside you see nothing abnormal. A brake and shifter who at first glance appear like are already known mechanical version. Also, the rear derailleur that is responsible for the changing of the pionkransjes, does not look out of striking. The small switching motor take hardly true.
The front derailleur, which is responsible for switching on the front of the small to the large chainring, the black housing is much more visible. And under the bottle cage it will be really special: here is the battery, half the size of a pack of cigarettes. The manufacturer assumes that frame builders in the future battery and power cables in the tubes calories.
Especially apparent when operating the front derailleur is electronically feeling noticeable: a sound like a spaceship from a science fiction movie. Not loud or obnoxious, but unquestionably electronically.
Strictly speaking, the circuit is more like "electric" to regard as the most important components;
two switching motors;
When combined brake and shifters are all almost the same place where it can be found in mechanical Shimano. Nevertheless indicates a test drive you should get used to it.
To switch to a larger chainring or sprocket, press both the mechanical and brake lever in EQUIPMENT electronic circuitry aside. Mechanically switching are clearly noticeable pressure points and you hear a faint clicking sound when getting on and off switching.
Not with the Di2: minimal contact of the switch is sufficient to select another gear. The short switching times and low power required, but will not appear for several hundred kilometers perceived as a real advantage.
But it all moves perfectly. The circuit has the mechanical Dura Ace as a base for years with Campagnolo Record and recently with the model of the American Red manufacturer Sram first choice for professional cycling. Dura Ace turns perfectly, electronic or mechanical, including steep slopes with full load on the pedals. The switching motors on the Dura Ace doing their job just as accurate as the derailleur cables with the mechanical counterpart.
Yes even a little better, because the Di2 solves a problem that, at least in theory, occur in mechanical chain circuits. Turn your rear gears from left to right or vice versa, there is a risk that due to the tilt of the chain, as they rub against the derailleur.
But this Shimano engineers have given the electronic circuit a little intelligence. Who "knows" how slanted the chain runs and automatically corrects the position of the front derailleur. As a result, there may be nothing more abrasion, even in an extremely inclined position of the chain, even though that because of increased wear is not to be recommended.
But in this piece of intelligence puts a tremendous amount of development work and Shimano would be stupid if they are no longer used. Because if the front derailleur automatically adjusts the position of the chain, the inside should not have too long been possible to produce a fully computer-controlled circuit.
Because the touring rider has not experienced the phenomenon that you have, in theory, although two or three front chainrings, but used in practice only one. For many, it is too laborious to also simultaneously with the front derailleur to operate the rear derailleur in order to achieve a smooth switching transition.