Yeah flywheels, that's the way to go.....

It would be cool if you could "windup" a 2 kg disc, mounted in a shell near the chainset on the flats. Of course you would need to go to some impossible speed, say 300,000rpm, and then engage it during climbs to assist the crank arms.

I doubt that such a transmission is possible, but in theory the practice would be a boon to many types of locomotion.

The flywheel idea with wheels or tires is flawed in one singular respect.

The additional energy required to add the inertia to the bicycle using heavy wheels isn't any more efficient in nature or timeliness during a given bicycle ride. In practice, the use of a "pumping action" and crank arms in bicycles makes rotational weight and acceleration critical shortcomings to cycling.

There's no such thing as being "up-to-speed", you continue to "pump" even when you think your spinning.......those heavy wheels would wear you out!

Gear ratios, knees, ankles and feet are no substitute for bearings and a camshaft........... too bad... My idea uses the solid idea of storing energy when under light load and returning it when under great load, weather the load be head-wind or a hill......