Figure 8-2.Components of a typical frame design.
accommodate the body and support the weight. They
are narrow toward the front of the vehicle to permit a
shorter turning radius for the wheels and then widen
under the main part of the body where the body is
secured to the frame. Trucks and trailers commonly
have frames with straight side members to
accommodate several designs of bodies and to give the
vehicle added strength to withstand heavier loads.
The CROSS MEMBERS are fixed to the side
members to prevent weaving and twisting of the frame.
The number, size, and arrangement of the cross
members depend on the type of vehicle for which the
frame was designed. Usually, a front cross member
supports the radiator and the front of the engine. The
rear cross members furnish support for the fuel tanks
and rear trunk on passenger cars and the tow bar
connections for trucks. Additional cross members are
added to the frame to support the rear of the engine or
power train components.
The GUSSET PLATES are angular pieces of
metal used for additional reinforcement on heavy-duty
With this type of frame construction, the body
structure only needs to be strong and rigid enough to
contain the weight of the cargo and resist any dynamic
loads associated with cargo handling and cargo
movement during vehicle operation and to absorb
shocks and vibrations transferred from the frame. In
some cases. particularly under severe operating
conditions, the body structure may be subjected to
some torsional loads that are not absorbed completely
by the frame. This basically applies to heavy truck and
not passenger vehicles. In a typical passenger vehicle.
the frame supplies approximately 37 percent of the
torsional rigidity and approximately 34 percent of the
bending rigidity; the balance is supplied by the body
structure. The most important advantages of the
separate body and frame construction are as follows:
Ease of mounting and dismounting the body
Versatility; various body types can be adapted to
a standard truck chassis.
Strong, rugged designs are achieved easily;
however, vehicle weight is increased.
Isolation of noise generated by drive train
components from the passenger compartment
through the use of rubber mounts between the
frame and the body.
Simplistic design that yields a relatively
inexpensive and easy manufacturing process.
Frame members serve as supports to which
springs, independent suspensions, radiators, or
transmissions may be attached. Additional brackets,
outriggers, and engine supports are added for the
mounting of running boards, longitudinal springs,
bumpers, engines, towing blocks, shock absorbers, gas
tanks, and spare tires.
INTEGRATED FRAME AND BODY
The integrated frame and body type of
construction (fig. 8-3) also referred to as unitized
construction, combines the frame and body into a
single, one-piece structure. This is done by welding the
components together, by forming or casting the entire
structure as one piece, or by a combination of these
techniques. Simply by welding a body to a
conventional frame, however, does not constitute an