Hi Daniele, this is the bicycle model. The first figure is the two-wheeled robot model. In the bicycle model, assuming there is no slip, the angular velocity of the front wheel is the same as the rear wheel. I guess he scenario you described is the two-wheeled robot which can has different velocity in two wheels. When V_leftwheel > V_rightwheel, it turns right. But the bicycle model is different, it have front and rear wheels which is not side by side. The front and rear wheels will have different velocity when it slips. But in the kinematic model, we assume there is no slip.