Car Script basic is vehicle controller script.
It uses standard Unity 5 Wheel Colliders.
Collider of car have to overlay Wheels. It is good idea to make low poly version of mesh for vehicle and set it as collider. Do not forget to turn on "Convex" for this mesh collider.
Depending on what car you are making - light sport car or heavy truck - first set approx. weight for it. Like 3 800 - 9 800 for the truck. Then, increase Motor Torque until you like how it looks.