During the 1982’ Championships there have been several accidents, including the one who killed Gilles Villeneuve, revealing of an increasing level of danger that resulted from the high performances reached by the wing-cars that exceeded the safety limits of the same single-seaters and of the race circuits.

Alarmed, the FIA ​​reacted immediately and in order to dramatically reduce the ground-effect produced by the wing profiles of the lower surfaces of the side pods of the vehicles in the different categories of motor sport.

The flat under floor surface was thus imposed by the technical regulation in 1983. Since then, it is the most secret area of a race car.

All teams try to hide, as much as possible, this area from the competitors’ curious eyes, because it is the most important part in the aerodynamic efficiency of these cars.

The biggest loads of negative lift are created there, applied precisely where they are needed most, on the rear axle.

From a flat surface, mandatory by the technical regulations since 1983, the lower surface of competition cars became more complex in order to limit the growing in its effectiveness in the generation of negative lift. Indeed, the fatal accidents of Roland Ratzenberger and Ayrton Senna on the GP of San Marino’ weekend in 1994, led the FIA ​​to establish a reference plan, the lower portion of the vehicle, above which then was defined the flat bottom or step plan, with a limited efficacy, due to the larger distance to the ground.

When we talk about flat under floor surface, we refer to the entire bottom surface of a Formula 1 car (or of most other categories of Formulas cars and Sport-Prototypes or DTM cars, for example) and that the technical regulation of 2005, the Year when I made ​​this work, corresponded, in the case of a Formula 1 car, to the area between two transversal imaginary lines located one 33 cm behind the front axle and the other 40 cm in front of the rear axle. Its width allowed by regulation, was a maximum of 140 cm, in the level of the step plan, who was 5cm above the reference plan, the width of which varied between 30 and 50 cm, positioned centrally and symmetrically along the longitudinal central line of vehicle and extending behind until the level of the rear axle.

Under the reference plan and along its entire length, is placed the "skid block", a wood device of 30cm wide, also imposed after the accidents of Senna and Ratzenberger, designed to prevent the cars to be tuned to run too close to the track, putting in risk the driver's safety, a situation that would be revealed by an abnormal wear of its surface.

This surface is conceived in a way that a Formula 1 car works as if it was a big inverted wing. It is discreetly lean, with the front lightly high, and so it forces the air that passes between this surface and the track, to a considerable acceleration, creating a negative pressure that is exercised in the area where the acceleration is larger, immediately before the rear limit of the step plan of the under floor, in it’s transition to the back diffusers.