The Copenhagen Wheel by Massachusetts start-up Superpedestrian is a replacement rear wheel for a bicycle that converts the energy of braking and descending into a battery-powered boost when the rider pedals uphill or wants more speed on flat ground.
The first examples of the $699 wheel are expected to ship in the first quarter of 2014, CNET reported Tuesday.
The lithium-ion battery in the 12-pound wheel recharges automatically when a rider descends a hill or pedals, Superpedestrian said in a statement.
"The Wheel is ridden like a normal bicycle -- users pedal and the motor phases in and out automatically," the company wrote. "The Wheel learns about the rider and intuitively recognizes how hard he or she pedals and the topography ahead to determine how much support the rider may need. There aren't any additional throttles, wires, or buttons, [thus] maintaining the pure simplicity of cycling."
The Copenhagen Wheel is available for single-speed bikes and, at additional cost, for multispeed bikes that change gears with a rear derailleur.
The wheel offers a 30-mile range and can propel a bike to speeds of 20 mph.