Automotive ground effects are an attempt to influence and control air to stabilize a car body when it is at speed. This process started in 1960s racecars and evolved into passenger cars since then.

Jim Hall's Chaparrals

Other racing designers used rear wings on racecars, but Jim Hall experimented and further developed the idea. On a long straight, the front of his Chaparral sports cars tipped up and the front wheels didn’t contact the ground because of the power shifting weight to the back. He put spoilers on the front to keep the front wheels in contact with the ground. His next innovation was to pivot the rear wing parallel to the ground on the straight to reduce the drag it created. It would pivot vertical to brake and stabilize the car going into the corners. He put the rear spoiler on poles above the car so it would contact clean air. This wasn't strictly automotive ground effects, but a step in that direction.

Chaparral

Chaparral race car.
Credit: Dan Wildhirt

The Sucker Cars

The first true ground effects car was the Chaparral sucker car. Lexan skirts sealed it around the bottom. A small two-stroke motor powered two fans that sucked air like a vacuum cleaner from under the car and pulled the vehicle to the ground. Because it used two motors the car was ruled illegal. In 1974 Formula I  Brabhams tried the fan concept. Racing organizations banned moveable aerodynamic parts and additional fans.

Underbody Automotive Ground Effect

Jim Hall’s Indianapolis Chaparral and the Lotus formula I car were among the first to apply the most successful use of Bernoulli concepts to automotive ground effects. If fluids, or air, flow through a constriction, speed rises and pressure falls. By using a smooth bottom with a bow in the middle, perpendicular to the length of the car, and skirts along the side will create a low-pressure area behind the bow. The Bernoulli vortex is enough to suck the car to the ground and increase stability and cornering speeds. This became the best ground effects application at the time. Lotus, and Mario Andretti, won the Formula I world championship in 1978 using this concept. Hall’s Chaparral used this idea to win the 1980 Indianapolis 500 and championship with Johnny Rutherford driving.

Modern Automotive Ground Effects

Racing organizations began to ban side skirts in the 1980s because of serious accidents. This was because if a side skirt becomes damaged, the pressure decreases rapidly, and the vehicle goes out of control.

Automotive ground effects use underbody designs with two tunnels that begin at the midpoint of the car for the most downforce and slope upward to the rear of the automobile. This still uses the Bernolli principle and produces a vortex to produce downforce and diffuse the air to a slower speed as the underbody area increases.

Front spoilers put more or less pressure on the front tires. They are balanced in conjunction with the rear wings to achieve balance in the car.

Automotive Ground Effects for Street Cars

Streetcar automotive ground effects control the air around, under and over the automobile. Adding components gives aerodynamic qualities, which will stabilize the car, and give it a sportier look. Front and rear air dams, and side skirts direct the air to the side of the car and prevent it from getting on the underside and causing  lift. A panel on the underside of the car will reduce drag.

Automotive Ground Effects Kits

The factory will install these components when purchasing the car. After market automotive ground effectskits are available. Several different suppliers manufacture automotive ground effect kits that can be put on automobiles. They can be removed or attached to existing bumpers and bodywork.

Automotive ground effects kits vary in price. Fiberglass components will break apart quicker than the tougher fiberglass resin parts, and priced accordingly.