The Green Wheel - 3 in 1 wireless electric bicycle hub motor is a self contained unit with batteries and motor in the single wheel set up.
The good part of that is that you can change wheels if you want a little motor assist on your pedal.
Also, you can put a Green Wheel on the front, back or both wheels for extra flexibility. And pedaling provides an additional assist for speed letting this puppy top out at almost 30 miles an hour!
Very cool!
