Chapter 1 The Automobile 5
Frame, Body, and Chassis
The frame and body are the two largest sections,
or parts, of a motor vehicle. The frame is the strong
metal structure that provides a mounting place for
all the other parts. The frame holds the engine, trans-
mission, suspension, steering, and other assemblies
in position.
The body is a steel, aluminum, fi berglass, plastic,
or composite (carbon fi ber) skin forming the outside
of the vehicle. The body is painted to give the vehi-
cle an attractive appearance.
The term chassis is often used when referring to a
vehicle’s frame and everything mounted to it except
the body—tires, wheels, engine, transmission, drive
axle assembly, and frame.
In body-over-frame construction, or full-frame
construction, the frame consists of thick steel mem-
bers. The chassis parts and the body bolt to this
frame. This heavy, strong design is used on vans,
pickup trucks, and sport-utility vehicles (SUVs).
Refer to Figure 1-3.
With unibody construction, sheet metal body pan-
els are welded together to form the body and frame.
Also called unit-body construction or unitized con-
struction, this is the most common design used to
build small and medium passenger cars. Unibody
construction reduces weight, improves fuel econ-
omy, and has a high strength-to-weight ratio. See
Figure 1-4.
Tech Tip
Because the frame is an integral part of the
body structure in a unibody vehicle, a unibody
chassis includes the unibody structure and
everything bolted to it except the bolt-on body
panels.
Figure 1-3. With body-over-frame construction, the chassis parts bolt to a strong perimeter frame. (Ford)