Every vehicle has a suspension system for it. The suspension is the part that holds the vehicle up, absorbs bumps, and allows it to steer. For the most part these systems wear out slowly, and with proper maintenance and periodic inspection they can be expected to experience only small, incremental problems. Sometimes the suspension will fail suddenly and dramatically and the vehicle will in effect fall down. This can be a couple of inches, until metal touches metal, and sometimes all the way only one or more wheels. This sort of sudden failure results when a spring or other weight-bearing part breaks, and is referred to as a collapse.