1, when the car through the uneven road surface to provide a buffer effect; 2, ensure that the wheels in a fixed Angle activities, so that the steering stability; 3. Weight of supporting wheels; 4, maintain good contact between the wheel and the road surface, ensure that the driving wheel and braking force generated between the wheel and the road surface can be transmitted to the car body; 5, car suspension is to meet the requirements of comfort, but also to take into account the requirements of handling stability, and they are often contradictory, the softer the spring, the more comfortable the ride. And the spring is too soft, there will be brake nod, unstable operation and other phenomena, so the design had to take the road of moderation, both aspects should be taken into account.