Single track vehicles including bicycles, motorcycles, and ski bikes stay upright when moving although they fall over at rest. Forces at the ground act on the vehicle as explained in this video. It is generally assumed that bikes stay upright by steering the front wheel in the direction of the fall. Much mathematical analysis is based on this idea with a coordinate system constructed to achieve centrifugal force to right the bike. I advance a simpler approach.
![](https://s2.save4k.ru/pic/pj1bRXOHkLQ/mqdefault.jpg)