A bicycle is basically an inverted pendulum ... The size of the stabilizing wheel could probably be reduced by replacing the 7.4 kg steel wheel with a Tungsten, Osmium, or Lead disk, possibly ...

The creators say that using the Rowbike can burn up to 50% more calories compared to riding traditional bikes. Rowbike is also available in a 4-wheel variant too. You can get a Rowbike for around ...