In equations of equilibrium, amounts of the tyre tread radius, gyroscopic couples due to wheels and engine as well as special properties of conventional models which have a large angle of lean and a small steering angle in rounding a curve are taken into account. And both results of calculations and experiments are well agreeable with each other. The angle of lean is always greater than the balancing angle of gravitational and centrifugal force. This is due to effects of large tyre tread radius and low position of mass centre. Moreover, the gyroscopic effect of engine is considerably intensive, especially in lower gear. The main reason why the motor-cycle has the property of oversteering is in the geometrical relation of the steering system. The side slip angle of tyre in single-trackers takes a far smaller value than that of four-wheeled vehicles.