Downforce
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Three different styles of front wings, all designed to produce downforce on the front wheels.
The term downforce describes the downward pressure created by the aerodynamic characteristics of a racing car that allow it to travel faster through a corner by holding the car to the track.
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's tires and suspension. The creation of downforce can only be achieved at the cost of increased aerodynamic drag (or friction), and the optimum setup is always a compromise between the two. Because it is a function of the flow of air over and under the car, downforce is directly proportional to the speed of the car and requires a certain minimum speed in order to produce the desired effect.
The amount of downforce that can be created is typically much greater for an open-wheeled Formula One or Indy car than for a full-bodied touring car or stock car because of its enhanced aerodynamic characteristics and the use of wings rather than spoilers.
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 airfoils.
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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 underside of the body is similar in shape to an inverted wing and creates an area of low pressure between the car and the track, pressing the car to the road. This is sometimes called a ground effect and has been the subject of many rule changes over the years in different racing series.
Airfoils
The amount of downforce created by the wings or spoilers on a car is dependent primarily on two things:
- The shape, including surface area, aspect ratio and cross-section of the device, and
- The device's orientation (or angle of attack).
A larger surface area creates greater downforce and greater drag. The aspect ratio is the width of the airfoil divided by its depth. Also, a greater angle of attack (or tilt) of the wing or spoiler, creates more downforce and more drag.
The rear wing of a modern 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 two-fold. 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 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.
