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Why ride a bicycle in the first place? Why not just walk?
People use bicycles to conserve their energy. With our feet stuck to the ground in walking we constantly transfer energy and momentum to the ground below us, never to be regained. When we ride bicycles, we conserve our momentum, we coast.
Every cyclist knows the thrill of reusing stored potential energy when coasting downhill. The hard earned climb is repaid in full with an effortless downhill coast. To walk, we work on both sides, the climb and the descent.
A bicycle with a human rider is one of the most efficient machines in existence due in part to the human metabolism and in part to the nearly frictionless conservation devices of axles and wheels.
There's not much room for improvement, but there is some.
In the spirit of the bicycle's energy conserving utility, CityBrakes seeks to further the overall ability of bicycles to conserve our pedal power.
CityBrakes would not replace conventional brakes. Instead, CityBrakes would be used for temporary decelerations often required by the stop-and-go nature of navigating a busy city's many small obstacles and tight turns.
With the strength and quality of modern drum-style coil springs it may be possible to employ a compact, relatively light-weight spring which can store up to 20 feet of braking deceleration for a typical cyclist riding at city speeds.
In operation, CityBrakes would decelerate the bicycle similarly to conventional brakes but the energy would be stored in the winding of a coil-spring. The spring is wound by a friction wheel which is brought into contact with the tire tread by the activation of a lever as in standard brakes. Either by release, or by a separate "triggering" control, a fast acting gear differential would reverse its position allowing the friction wheel to now supply forward-acting drive in the amount already stored during braking.
The result of braking with CityBrakes is a pedal-free return to your prior speed with only small losses to friction. However, CityBrakes returns energy precisely at the time we need it most: powering up from a slow-down. It is always just after a near-stop that pedaling requires the most exhausting and least efficient pedaling. CityBrakes seeks to alleviate this strain and increase the overall conservation, range, and enjoyment of bicycling.