Electronic Shifting

Basically built around "stepper motors" and position sensors integrated on/within the derailleurs and sensors within the shifters . Rather than a manual cable being used to connect shifter to derailleur, a wire is used. Similar to cars with accelerator-by-wire and steer-by-wire controls. When all the kinks have been worked out and they work, electronic controlled systems have greater precision than manual- driven systems. Fewer mechanical components subject to friction, wear, etc.

The transition is somewhat analogous to moving from friction-based shifting systems to indexed, where "detents" built into the shifters Index (match) the position of the derailleurs in line with cogs and chainrings. As most cyclists experience, cable stretch, wear, and other factors, require micro and macro adjustments to re-align the shifter detents with changes in the system. With friction based shift systems, every shift was a macro/micro adjustment that required a degree of experience and finesse. The electronic system eliminates mechanically related variances due to cables and related component wear, however, mechanical chain, gear, and derailleur wear still exists and has to be accommodated. Due to the added level of position sensing and precision, things like cage trim can be automatically programed.

In the automobile world, some people still prefer to dive manual transmissions and others some type of "automatic" - either generic, sequential shift, constant velocity/continuously variable , etc. At the highest levels of racing, F1 moved to electronic controlled shifting decades ago. Many "average joes" continued to hold firm to the idea that manual shifting provided skilled drivers with a competitive advantage. Not too long ago in Porsche circle this was a fierce debate - tiptronic or manual - which was faster. Side-by-side results demonstrated the edge went to tiptronic more often than not. Diehard manual lovers continue to disagree.

It is ironic that the company (Shimano) which cleaned Suntour's clock when Suntour bet the farm on the automatic Browning system in the early 90's would be the one to resurrect the concept. Suntour never worked all the kinks out - probably because the cost of precision technology at that time proved to be too great for a system than could be manufactured with any significant market demand. It's still expensive but less so in relation to precision manually indexed controls.

I have yet to try DI2 myself, but probably will at some point. I've adopted tiptronic for my daily car, but have an older manual transmission sports car which just adds something special/different to the experience. I suspect the world of bicycles won't be much different than the automotive world.