> a sort of vaccum effect to keep the car sucked to the ground

Ground effect[0], thoroughly used in LMP to gain downforce without suffering as much drag as with a wing.

Here's what happens when the effect breaks down[1].

[0]: http://en.wikipedia.org/wiki/Ground_effect_(cars)

[1]: http://www.youtube.com/watch?v=TIJ4q3PD57A