If a road were perfectly flat, suspensions wouldn’t be necessary. But roads are far from flat. Even freshly paved highways have bumps and divots that can interact with the wheels of a car, jogging it up and down.
Without a suspension, those bumps would go right to the frame of the car. The wheels would lose contact with the road, then slam back into the road surface — giving you the comfort-free (and hard-to-steer) ride of a toy wagon. But with a suspension, the body of the car moves forward smoothly while the wheels follow bumps in the road.
Auto suspension has 3 important jobs:
- Keeping tires on the road surface. Engineers call this “road holding”. It’s important for the tires to stay in contact at all times, because friction between the tires and the ground is what lets the car accelerate, stop and corner. The suspension keeps the weight centered to maintain the grip.
- Stable steering and handling. The suspension keeps the car or truck body from tipping or rolling in a corner.
- Passenger comfort. Keeps the cabin isolated from the bumps on the road. Suspensions absorb that up-and-down energy and disperse it without too many bobbles.
The entire suspension has many parts, including the springs, shocks and/or struts, and their connections to the steering and the chassis. The whole thing has to balance the different jobs of steering and comfort for a given car or truck. A luxury car, has a suspension designed for a very soft and cushy ride. So it compromises with less stability in the steering and more body roll. A sporty car will stick to the curve better, but you’ll feel bumps in the road more.
The parts of the suspension take a lot of abuse over time — that’s their job. So they do wear out eventually.