Originally Posted by uncleto
I was under the impression that a wing's function is the creation of downforce while a spoiler's is to disturb the laminar flow over the top of the vehicle.
If I may gently pick a nit - a spoiler has many purposes to the aerodynamicist, and in some cases disturbing of laminar flow can produce downforce.
(By the way, the wikipedia articles on spoilers and car aerodynamics in general are completely wrong. I read the articles and they have comments like "Spoilers are almost always ignored in racing applications" (I am not kidding) which makes me wonder if the author of the Wikipedia article has ever watched a lemans, dtm, or even NASCAR race, let alone any other kind of motorsport.)
It's common on aircraft to view spoilers as a way to disturb laminar flow (and hence cause boundary layer separation and therefore reduce lift) on wings. However, cars are significantly different from aircraft. Why? Because of two reasons:
1. Automobiles want downforce, not lift.
2. Automobiles experience "ground effect". Normal aircraft do not.
Spoilers on automobiles have a vastly different function on cars than on aircraft due to "ground effect". More specifically, if it's possible to create pressure differentials on a car, then it's possible to create downforce.
Ground effect makes it possible to reduce underbody air pressure by using a splitter and relatively flat undertrays, along with undertray angle and venturis. However, the downforce produced can be multiplied by using a front and rear spoiler. In this case, front spoilers are used to create downforce by rapidly decreasing the airflow directly above the front splitter. As the boundary layer is destroyed, so the air velocity decreases significantly. Higher pressure on top with lower pressure on the bottom means a force is exerted - hence downforce.