Downforce

Three different styles of front wings from three different Formula One eras, all
designed to produce downforce at the front end of the respective race cars. Top to
bottom: Ferrari 312 (1979), Lotus 79 (1978), McLaren MP4-10 (1995)

The term downforce describes the downward pressure created by the aerodynamic
characteristics of a car that allows it to travel faster through a corner by increasing
the pressure between the contact area of the tire and the road surface, thus creating
more grip.

Fundamental principles

The same principle that allows an airplane to rise off the ground by creating lift
under 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 mass
repartition, tires and suspension. The creation of downforce by passive devices
almost always can only be achieved at the cost of increased aerodynamic 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; some drivers also
make different choices on setup. Because it is a function of the flow of air over and
under the car, and because aerodynamic forces increase with the square of velocity,
downforce increases with the square of the car's speed and requires a certain
minimum speed in order to produce a significant effect. But some cars have had
rather unstable aerodynamics, such that a minor change in angle of attack or height
of the vehicle and this can cause large changes in the downforce. In the very worse
cases the can cause the car to experience lift, not downforce, for example, caused
by a bump on the track or slipstreaming over a crest, and sometimes can have
disastrous consequences. A notorious example of this was Peter Dumbreck's
Mercedes-Benz CLR in the 1999 Le Mans 24 hours, 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

Most racing formulae have a ban on aerodynamic devices that can be adjusted
during a race, except at pit stops.

The bottom panel of the Panoz DP01 ChampCar exhibiting complex aerodynamic
design.

The underside curves of the Panoz DP01 ChampCar.

Where:

• D is downforce in newtons
• WS is wingspan in metres
• H is height in metres
• AoA is angle of attack
• F is drag coefficient
• ρ is air density in kg/m³
• V is velocity in m/s

The body

The rounded and tapered shape of the top of the car is designed to slice through the
air and minimize wind resistance. Detailed pieces of bodywork on top of the car
can be added to allow a smooth flow of air to reach the downforce-creating
elements (i.e., wings or spoilers, and underbody tunnels).

The overall shape of a street car resembles an airplane wing with air flowing over
it faster than the air flows under it causing a difference in air pressure. Almost all
street cars have aerodynamic lift as a result of this shape. There are many
techniques that are used to counter balance a street car. Looking at the profile of
most street cars the front bumper has the lowest ground clearance followed by the
section between the front and rear tires, and followed yet by a rear bumper usually
with the highest clearance. Using this method, the air flowing under the front
bumper will make it's way back to the rear bumper where it has a larger volume
and thus a lower pressure. Race cars will exemplify this effect by adding a rear
diffuser to better control the pressures directly under the rear bumper. Other
aerodynamic components can befound on the underside to improve downforce
and/or reduce drag include a splitter and a diffuser and vortex generaters.

Airfoils

The amount of downforce created by the wings or spoilers on a car is dependent

A larger surface area creates greater downforce and greater drag (also known as air
resistance). The aspect ratio is the width of the airfoil divided by its depth. The
aspect ratio formula is written like AR=b squarded/s, where AR=aspect ratio,
b=spand squared, and s=wing area. Also, a greater angle of attack (or tilt) of the
wing or spoiler, creates more downforce, which puts more pressure on the rear
wheels and more drag.

The rear wing of a 1998 Formula One car, with three aerodynamic elements (1, 2,
3). The rows of holes for adjustment of the angle of attack (4) and installation of
another element (5) are visible on the wing's endplate.

Front

The function of the airfoils at the front of the car is twofold. They create
downforce that enhances the grip of the front tires, while also optimizing (or
minimizing disturbance to) the flow of air to the rest of the car. The front wings on
an open-wheeled car undergo constant modification as data is gathered from race
to race, and are customized for every characteristic of a particular circuit (see top
photos). In most series, the wings are even designed for adjustment during the race
itself when the car is serviced.

Rear

The flow of air at the rear of the car is affected by the front wings, front wheels,
mirrors, driver's helmet, side pods and exhaust. This causes the rear wing to be less
aerodynamically efficient than the front wing, Yet, because it must generate more
than twice as much downforce as the front wings in order to maintain the handling
to balance the car, the rear wing typically has a much larger aspect ratio, and often
uses two or more elements to compound the amount of downforce created (see
photo at left). Like the front wings, each of these elements can often be adjusted
when the car is serviced, before or even during a race, and are the object of
constant attention and modification.

Wings in unusual places

Partly as a consequence of rules aimed at reducing downforce from the front and
rear wings of F1 cars, several teams have sought to find other places to position
wings. Small wings mounted on the rear of the cars' sidepods began to appear in
mid-1994, and were virtually standard on all F1 cars in one form or another, until
all such devices were outlawed in 2009. Other wings have sprung up in various
other places about the car, but these modifications are usually only used at circuits
where downforce is most sought, particularly the twisty Hungary and Monaco
racetracks.

The 1995 McLaren Mercedes MP4/10 was one of the first cars to feature a
"midwing", using a loophole in the regulations to mount a wing on top of the
engine cover. This arrangement has since been used by every team on the grid at
one time or another, and in the 2007 Monaco Grand Prix all but two teams used
them. These midwings are not to be confused either with the roll-hoop mounted
cameras which each car carries as standard in all races, or with the bull-horn
shaped flow controllers first used by McLaren and since by BMW Sauber, whose
primary function is to smooth and redirect the airflow in order to make the rear
wing more effective rather than to generate downforce themselves.

A variation on this theme was "X-wings", high wings mounted on the front of the
sidepods which used a similar loophole to midwings. These were first used by
Tyrrell in 1997, and were last used in the 1998 San Marino Grand Prix, by which
time Ferrari, Sauber, Jordan and others had used such an arrangement. However it
was decided they would have to be banned in view of the obstruction they caused
during refueling and the risk they posed to the driver should a car roll over. (It is
rumored that Bernie Ecclestone saw them as being too ugly on television and
therefore had them banned.

Various other extra wings have been tried from time to time, but nowadays it is
more common for teams to seek to improve the performance of the front and rear
wings by the use of various flow controllers such as the afore-mentioned "bull-
horns" used by McLaren.