Originally Posted by NoCones
My guess is that the spoiler doesn't so much "create downforce" as it "reduces lift" at speed. As mentioned above, the profile of the car is somewhat like an airfoil and therefore it creates some lift, especially as velocity increases...that lift relies on a nice smooth, undisturbed (laminar) flow of air over the top of the vehicle...the spoiler...well... "spoils" that flow and lessens the tendency to create lift.
Bryan
(B.S., aerospace engineering)
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. This would reduce lift, as well as reducing the low pressure pocket behind the vehicle (therefore reducing drag). I imagine that a spoiler may also produce a small amount of downforce, but it is a secondary effect and not the primary purpose of the device. While reducing lift and producing downforce may have the same effect on steering, to me they seem to be different approaches with different engineering solutions (wings vs spoilers).