The elephantine rear airfoil bolted to the rear deck of the Dodge Viper ACR is not only highly functional, but it gets credit as being the first mass-produced carbon fiber-reinforced polymer (CFRP) wing on a production car. Rear wings on high performance vehicles are designed to counter lift. Without aerodynamic aids, most vehicles become less stable and have reduced grip as velocities increase (worst case, the vehicle actually flies as did the Mercedes CLR at Le Mans in 1999).
The faster a car goes, the more downforce its various wings, spoilers and splitters can produce. There's always a trade-off though, as the byproduct of downforce is more drag, which reduces a car's top speed. Supercars like the Bugatti Veyron use active aerodynamics to produce the right amount of downforce for a specific situation like twisty road courses or high-speed runs, but cars like the Veyron are out of reach for most. Enter AeroMotions, a company that promises its rear wing assembly will