Racing cars capable of moving at speeds well in excess of 100 m.p.h. need aerofoils to counter the effect of lift created by their highly streamlined shapes.
Drag is caused by the turbulence of the air as it flows in to fill the vacuum left behind a forward moving object. The less streamlined the object, the greater the space to be filled in and the greater the turbulence. Therefore, the greater the “drag”.
As designers improve the streamlining effect of racing cars to reduce drag, the cars’ shapes become more and more flattened and a new problem arises. The car has taken on similar properties to an aircraft wing and the movement of air over and under it at high speed begins to provide lift.
The aerofoil placed at the rear of the car is so designed as to create a downward force when it passes through air at speed, and thus counteracts the lift. If this did not occur the cars’ wheels would make too little contact with the road surface and the driver would quickly loss control.
Picture credit: google