| Downforce is based on the Bernoulli Effect. The Bernoulli Effect is what causes planes to fly. Plane wings are designed to more air faster across the top of the wing than the bottom. The slower air, with higher pressure, naturally tries to mix with the lower pressure air, to atain equlibrium.
Downforce does the opposite. The air moves faster underneath the car, causing the high pressure air to push down on the car in order to reach the lower pressure air.
The McLaren F1 is one of the greatest examples of high downforce. At high enough speeds the McLaren is able to drive upside-down without loss of traction on the road!
To bad there aren't many streets that suddenly invert... or too many chances to drive a fucking McLaren! huh? | 
