I have no idea how efficient this is but this is what the manufacturer says: The Dekra D-Drive uses a drive shaft to transmit power from the bike pedals to the rear wheel. This drive shaft employs a fully-enclosed bevel gear system made of a lightweight, yet highly durable, aluminum alloy. Shimano internal gears within the rear wheel enable the D-Drive system to deliver smooth, quiet performance while optimizing pedaling efficiency. MORE PICS->
Via Gizmag & DekraBikes
