In the case of cars and other light vehicles, the chassis includes everything beneath the waistline of the body and is considered one piece. Most are constructed of welded pressed steel sections in unit form. Body parts such as hoods, roofs, doors, trunks, and fenders can be replaced.
For heavy roadgoing and offroad equipment (buses, off-highway and construction machinery), heavy trailers, the chassis consists of a heavy frame of steel channels, angles, or extruded aluminum bolted or welded together, with springs, axles, brakes, wheels, engine, cooling and power system components, fuel tanks, lights, instruments, cab or controls. Body parts mounted to bolted (or sometimes removable, welded-on) brackets bolted (or welded) to the frame do not include engine, power transmission to wheels components mounted in or on frame.
