Editing Downforce (section)

==Fundamental principles==
The same [[Bernoulli's principle|principle]] that allows an airplane to rise off the ground by creating [[Lift (force)|lift]] from its wings is used in reverse to apply force that presses the race car against the surface of the track. This effect is referred to as "aerodynamic grip" and is distinguished from "mechanical grip", which is a function of the car's mass, tires, and suspension. The creation of downforce by passive devices can be achieved only at the cost of increased aerodynamic [[drag (physics)|drag]] (or [[friction]]), and the optimum setup is almost always a compromise between the two.

The aerodynamic setup for a car can vary considerably between race tracks, depending on the length of the straights and the types of corners. Because it is a function of the flow of air over and under the car, downforce increases with the square of the car's speed and requires a certain minimum speed in order to produce a significant effect. Some cars have had rather unstable aerodynamics, such that a minor change in [[angle of attack]] or height of the vehicle can cause large changes in downforce. In the very worst cases this can cause the car to experience lift, not downforce; for example, by passing over a bump on a track or [[slipstreaming]] over a crest: this could have some disastrous consequences, such as [[Mark Webber (racing driver)|Mark Webber]]'s and [[Peter Dumbreck]]'s [[Mercedes-Benz CLR]] in the [[1999 24 Hours of Le Mans]], which flipped spectacularly after closely following a competitor car over a hump.

Two primary components of a racing car can be used to create downforce when the car is travelling at racing speed:

* the shape of the body, and
* the use of [[airfoil]]s.

Most racing formulae have a ban on aerodynamic devices that can be adjusted during a race, except during [[pit stop]]s.

[[Image:2007'11-PanozDP01-BottomPanel-crwp.jpg|thumb|right|The [[Carbon Fiber|CFRP]] floor of the [[Panoz DP01]] [[ChampCar]] exhibiting complex aerodynamic design.]]

[[Image:2007'11-PanozDP01-UndersideAero-crwp.jpg|thumb|right|The underside curves of the [[Panoz DP01]] [[Champ Car]].]]

The downforce exerted by a wing is usually expressed as a function of its [[lift coefficient]]:

:<math>F = -C_L \frac{1}{2} \rho v^2 A</math>

where:
*''F'' is downforce (SI unit: [[Newton (unit)|newton]]s)
*''C<sub>L</sub>'' is the [[lift coefficient]]
*''ρ'' is [[air density]] (SI unit: kg/m<sup>3</sup>)
*''v'' is [[velocity]] (SI unit: m/s)
*''A'' is the area of the wing (SI unit: meters squared), which depends on its [[wingspan]] and [[Chord (aeronautics)|chord]] if using top wing area basis for ''C<sub>L</sub>'', or the wingspan and thickness of the wing if using frontal area basis

In certain ranges of operating conditions and when the wing is not stalled, the lift coefficient has a constant value: the downforce is then proportional to the square of airspeed.

In aerodynamics, it is usual to use the top-view projected area of the wing as a reference surface to define the lift coefficient.