Electronic gear shifting

Electronic gear shifting is a way of shifting gears on a bicycle. It lets bicycle riders use a switch to shift gears, instead of a lever. Electronic gear shifting can be faster than shifting gears with a lever.

How it works

The standard system for gearing up and down works with bowdens. A bowden is special kind of wound steel cable, which connects levers to the shifter, derailleur or brakes. As the rider pulls or taps a lever, the bowden reacts at the same time. That causes the bicycle to change gear.

Electronic works without bowdens. The system is digital. There is no wound steel cable. Instead, there are multiple combinations of 0 and 1. A battery placed under the frame powers the system. Each battery should last for 1000 km depending on the manufacturer. Then it needs to be recharged.  Wires for data and power are hidden inside the frame. Parts of the shifting systems are connected to each other. Servomotors do the shifting. The shifter and derailleur have a pair of servomotors built into them.  There is a self-adjustable microchip in the derailleur. The system has its own logic, which keeps the chain from dropping. There is no need for maintenance because the derailleur adjusts itself using the microchip.

Pros and cons
Pros:
Speed of shifting       
Ease of shifting (no need to push hard, a tap is effective)                     
Self-adjusting derailleur
Less weight
Less maintenance
Comfort

Cons:
Price ($2000+)
Battery capacity
No option for multiple shifting

Manufacturers

Shimano – Di2 Ultegra/Dura ace series (since 2009)
Campagnolo  - (since 2011)

 References 

Category:Human-powered vehicles
Category:Mechanics