When people think of automobile performance, they normally think of horsepower, torque and zero-to-60 acceleration. But all of the power generated by a piston engine is useless if the driver can't control the car.
The job of a car's suspension system is to maximize the friction between the tires and the road surface, to provide steering stability and good handling. In this article, we'll explore how a car's suspension system i.e. tires, springs, shock absorbers and links that connect to the vehicle work cohesively to provide a comfortable drive.
If a road were perfectly flat, with no irregularities, suspensions wouldn't be necessary. But roads are far from flat. Even freshly paved highways have subtle imperfections that can interact with the wheels of a car. It's these imperfections that apply forces to the wheels. According to Newton's laws of motion, all forces have both magnitude and direction. A bump in the road causes the wheel to move up and down perpendicular to the road surface. The magnitude, of course, depends on whether the wheel is striking a giant bump or a tiny speck. Either way, the car wheel experiences a vertical acceleration as it passes over an imperfection.
Without an intervening structure, all of wheel's vertical energy is transferred to the frame, which moves in the same direction. In such a situation, the wheels can lose contact with the road completely. Then, under the downward force of gravity, the wheels can slam back into the road surface. What you need is a system that will absorb the energy of the vertically accelerated wheel, allowing the frame and body to ride undisturbed while the wheels follow bumps in the road.
The study of the forces at work on a moving car is called vehicle dynamics, and you need to understand some of these concepts in order to appreciate why a suspension is necessary in the first place. Most automobile engineers consider the dynamics of a moving car from two perspectives:
Ride - a car's ability to smooth out a bumpy road
Handling - a car's ability to safely accelerate, brake and corner
These two characteristics can be further described in three important principles - road isolation, road holding and cornering.