Hi, I have been trying to find some information on the forces acting on the wheel when the vehicle is moving but I am a little bit confused. I would be grateful if someone explain me the basic principles. What I understood so far is; (assuming front wheel drive) * when the car is stationery; there is a torque applied to the wheel and this is less than the "static friction force". * When a torque equal to the static friction is applied the wheel starts rolling. And at that moment static friction disappears and a "dynamic friction" comes to stage and this is usually smaller than the static friction. As long as the torque is equal to the resisting forces then the wheel rolls at a constant speed. * And if a bigger force is applied the car accelerates at a rate proportional to the difference between the "torque" and "dynamic friction+air resistance". The things I don't understand are; - I still don't know if the drag force and rolling resistance and dynamic friction are all same thing? - "hysteresis" is also another grey area for me. I understand that it is a force couple caused by the difference in pressure between the front and the rear contact lines of the front wheel. This is generating a moment resisting to the torque applied. Is this the force I called "dynamic friction" or an additional resistance? Because if it is the only resisting force between the wheel and the surface I find it very difficult to understand how this "couple" can provide the movement at a very low speed (say 1 second after the car starts moving). Because at a low speed the distance between the couple will be very very small? Any help appreciated. Thanks in advance.