As a child, learning to ride a bike vexed me to no end. While my friends zipped around the neighborhood on two wheels, I plodded along on four, thanks to an embarrassing set of “training wheels.” Good ...

Back in 1967, California-based Gyro Transport Systems built a prototype vehicle known as the Gyro-X. The automobile had just two wheels, one in front and one in the back and, as the car’s name implies ...