8 Section 1 Introduction to Automotive Technology
engineering, aerodynamics is the study of the
resistance to airfl ow over and under the car body
at highway speeds. Aerodynamic drag is the “worst
enemy” to good gas mileage.
The goal of auto manufacturers is to design a vehi-
cle with a very low drag, or resistance to movement
through the air. This is done by designing cars with
very small frontal cross-sectional areas. The height
and width of the car body should be very small. A
vehicle with a small cross-sectional area produces
less resistance to airfl ow than a vehicle with a large
cross-sectional area. Refer to Figure 1-7.
Coeffi cient of drag (Cd) is a number that repre-
sents the force required to move a passenger vehicle
through air. A good Cd for a small sports car is 0.26.
The Cd for a larger vehicle, such as a truck or van,
might be as high as 0.40. Fuel economy is reduced
by an increase in Cd, as the vehicle has to push more
air out of its way when moving.
Vehicle Body Types
Automobiles are available in several models,
or body types, including the sedan, convertible,
hatchback, station wagon. In addition, the mini-
van, crossover vehicle, sport-utility vehicle (SUV),
pickup truck, and micro car have become increas-
ingly popular.
A sedan is a car that has front and back seats and
will carry four to six people. Both two-door and
four-door sedans are available. They have center
body pillars, or “B” pillars, between the front door
and rear quarter panel, Figure 1-8A.
A convertible has a roof panel that can be raised
and lowered into a well located behind the back
seat. The convertible roof can be made of metal, a
composite, or a synthetic fabric. Metal roofs fold into
the trunk area. A convertible has no door pillars, and
its strength is designed into the center area of the
frame or fl oorpan. Most convertibles are two-door
models, Figure 1-8B.
A hatchback, or liftback, has a large rear door for
easy access when hauling items. This style car is avail-
able in three- and fi ve-door models, Figure 1-8C.
A station wagon has a long, straight roof that
extends all the way to the rear of the vehicle. Station
wagons have large rear interior compartments and
come in two- and four-door models, see Figure 1-8D.
A full-size van has a large body for large fami-
lies or commercial service. The minivan is midsize
and similar to the station wagon, but it has a higher
roofl ine for more headroom and cargo space. Most
minivans are designed to carry seven passengers.
See Figure 1-8E.They are usually front-wheel drive.
A pickup truck is a front-engine, cab-forward vehi-
cle with a large, open cargo area in the rear. Full-size
pickups use a perimeter frame made of heavy gauge
steel. The cab, bed, fenders, and other body panels
are bolted to the frame. Rubber bushings fi t between
body panels and the frame to prevent noise and
vibration from entering the passenger area.
Figure 1-7. A low-slung car body with smooth shapes and a small frontal cross-section decreases aerodynamic drag and amount
of power needed to keep the vehicle moving at any speed. The trend is moving away from heavy SUVs and trucks to smaller
vehicles that get better gas mileage. (Mazda)