Automobiles started using aerodynamic body shapes in the early part of their history. As engines became more powerful and cars became faster, automobile engineers realized that wind resistance significantly hindered their speed. The first cars to adopt improved aerodynamics, or streamlining, were racing cars and those attempting to break the land speed record.
"Dreamers, engineers, racers and entrepreneurs were lured by the potential for the profound gains aerodynamics offered," wrote Paul Niedermeyer, author of "Automotive History: An Illustrated History Of Automotive Aerodynamics," on the website Curbside Classic. "The efforts to do so yielded some of the more remarkable cars ever made, even if they challenged the aesthetic assumptions of their times."
Regarding the aerodynamics of a racing car, Dr. Joe David, professor of mechanical and aerospace engineering, and known as "Mr. Stock Car" at North Carolina State University, said, "Most of the horsepower generated by a racing engine is eaten up by the high-pressure air pushing the front of the car and the low-pressure air — a partial vacuum — dragging at the car from behind."
However, drag cannot be the only consideration. While lift is desirable for an airplane, it can be dangerous for an automobile. In order to maintain better control for steering and braking, cars are designed so the wind exerts a downward force as their speed increases. However, increasing this downward force increases drag, which in turn increases fuel consumption and limits speed, so these two forces must be carefully balanced.
Many classes of racing cars use movable winglike airfoils to adjust the downward force of the air on the car. When setting up a racing car, one must also consider turbulence caused by other cars on the track. This requires setting the airfoils on the car to produce a greater downward force during the race than is needed for qualifying when the car is on the track by itself. This is why lap times during qualification are usually much faster than they are during the race.
Many of the same aerodynamic principles used in racing also apply to regular cars and trucks. Automotive engineers use computer simulations and wind tunnel experiments with scale models and actual vehicles to fine-tune the aerodynamics of automobiles so they generate the optimum amount of downward force to the front and back wheels with the least possible amount of drag.