I just watched this video that perfectly explains how to derive the equations for the slip angle of a car: However, how could this be done for a three axle system (car-trailer)? Would you have to express distance a (in the video) in terms of b (distance from centre of gravity to the second axle)? I understand that moments could not be transferred through the hitch of the trailer. But then what would need to be done? Will the centre of mass be much closer to the back of the vehicle? Would the slip angle of the wheels on the trailer need to be separately derived? If so, how would that be done?