Simple vechicle simulation : generating particles at a specific point and applying forces on wheels rather than the body?

Hi Guys , I am new game development so please excuse my knowledge in Unity. I was trying to build a simple vechicle simlation in unity and have came upon a lot of problems actually getting it to work ( i have seen a lot of tutorials , one way or anothere they don't actually fit into my model) So the first question is , how can i apply the forces to move the vechicle on its wheels rather than the main chasis ( so that i can switch between front and rear wheel drive) and also can i apply a physics material to just the wheels? ( dragging and dropping didn't work :-( ), and how can i display a particle system on a specific point on the car , such as sparks when the vechicle hits somewhere..

Any help would be greatly appreciated

Thanks in advance