Downforce is a downward force produced by air pressure, which creates a stronger pressure between the tire and the surface of the road. The principle involved is the same as the one that gives lift to airplanes, but in reverse.
Aerodynamic force results from differences in pressure on the sides of the moving object. The most common methods for increasing the downforce of a vehicle involve reducing the air pressure underneath the vehicle.
For the most part, any increase in downforce will also bring an accompanying increase in aerodynamic drag. For the speed demon, more drag means lower speeds on the straightaway But more downforce means better handling on turns since the tires grip the track more securely.
Automotive engineers and pit crews strive to keep the two forces in balance. On a track like Daytona, with its long straightaways and banked, sharp corners, the designs tend toward keeping drag to a minimum. For short-track racing, the strategy is reversed -- because the driver spends more of the race negotiating curves, an emphasis on downforce will lead to greater overall speed as well as increased safety [source: Tierney].
Attaining more downforce by manipulating racecar bodies is an obsessive task in the stock car business. Perhaps the best place to start is at the nose of the vehicle. A properly angled nosepiece, placed low to the ground, directs the majority of the air upward over the top of the car. The objective is to create a low-pressure area, or partial vacuum, underneath the nose [source: Circle 304].
The wheel wells are another area to shape. A flared wheel well opening, in front of the tire, will force onrushing air away from the sides and bottom of the car, further decreasing the air pressure [source: Boone, "Race Car Aerodynamics"].
For all of the technological prowess devoted to building up downforce behind the front wheels of the stock car, it's critical to consider balance. The back of the car must have its share of downforce to handle properly.
Studying downforce means paying attention to its opposing force, lift.