A team of scientists from an American university say they have reinvented the bicycle wheel.
The Copenhagen Wheel is a hub containing motor and batteries which can be fitted to the rear wheel of almost any bike, providing a boost to the cyclist whenever needed, say developers.
It has been unveiled at the UN Climate Summit by the team from the Massachusetts Institute of Technology.
Commentary from the BBC's Martine Croxall.
Original Article: BBC News - Scientists unveil 'bicycle innovation' in Copenhagen [Video]