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. 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).
You are correct concerning the operation of both wing and spoiler, but to be clear, both a spoiler and wing can produce downforce. They do so in slightly different ways. A spoiler is used to create a high-pressure area which produces a downforce via pressure differential. This assumes that the underbody is a low-pressure area.
If the area above the car at the spoiler is at 30psi and the area under the car's spoiler is 15psi, then a force of 15psi is exerted on the area of the car covered by the spoiler.
Therefore, I'm not sure it's correct to say that the primary purpose of a spoiler is not to create downforce. The spoiler is an aerodynamic aid, such as a gurney flap or a leading-edge flap. In the end, the literature and car magazines that I have read point to the Crossfire spoiler being designed for production of downforce, so I assume naturally that the primary purpose of the crossfire spoiler is downforce.