The function of a rear spoiler is to control the flow of air streaming over a vehicle and properly manage it when it reaches the rear where turbulence is most likely to form. A correctly designed spoiler will counteract the lifting forces that most cars experience when speeds get high, and it will enhance rear grip by keeping a vehicle’s rear end planted firmly against the road – without causing excess drag.
While aerodynamics do not play as huge a role at U.S.-legal speeds, they can make the difference between life and death on racetracks or high-speed German autobahns. In fact, the absence of a spoiler or the presence of one with a faulty design can actually cause a car to lift off the road surface when velocities reach extra-legal road speeds. All control is lost at that point, and a vehicle can end up sailing off in an untold direction – with disastrous results. So one important question to ask is which type of spoiler is right for you and your driving style.