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Why do we need down-pressure?

Miroslav Sanytrák | 2.6.04 | Přední křídlo

F1 constructor

Pic. 1

Any performance car is expected to turn fast. A car in a bend is pushed out by the centrifugal force, see OS in the pic.1. There are the friction forces between the tyres and the road, working against. As soon as the centrifugal force gets bigger than the total of the friction forces T, the car starts skidding, leaves the road or loses the ideal performance in the bend. The friction force may be obtained as T = f . NC, whereas f is the friction coefficient, NC is the component force taken from the car's weight and the down-pressure NA. The friction coefficient, f, depends mostly on the tyre's mix compositon, the intensity of NC then on the aerodynamic design of the spoiler and other details of the body and chassis. The weight component is usually determined by the given car weight.

Pic. 2
However, the component of the force given by the weight of the car may be reduced by aerodynamic lift emerging under the floorboard. Performance cars tend to be low to get the centre of gravity low. In short - at a certain - high - speed there occurs a phenomenon which may be described as an aerodynamic clogging (seeZ in the pic.2). It is caused by the depth of the foundary layer, in which the bypassing medium ‘flows' more slowly but the car surmounts this barrier with its power. The air pressure under the floorboard increases, the aerodynamic lift rises and tends to lift the car. It is this force that the spoilers must diminish. If the down-pressure is bigger, the friction forces between tyres and the road are bigger allowing the car to turn faster. Of course, this is just a simple diagram, because the bigger down-pressure the wing generates, the bigger aerodynamic resistance it has, therefore its maximum down-pressure in a bend does not always has to be an optimal solution. It may cause a major slow-down of the car in straight parts.
Nose detail
A different nose
Other type of nose
And another nose
Detail of another nose

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