A suspension system comes in two different designs—independent and solid (live) axle. Most cars use an independent suspension system, where each wheel moves up or down independently without affecting the other wheels. Some cars and most trucks use a solid axle suspension in the rear, where the axle moves up and down like a seesaw and the movement of one wheel causes a corresponding movement in the other wheel.
Vehicles with independent suspension systems offer a more comfortable ride and have better handling characteristics. Solid axle systems are stronger, less expensive to build, and have more load bearing capacity, but offer a rougher ride.