TYRE PRESSURES Endurance racing, and more particularly the Le Mans 24 Hours, is the only form of motor racing where the drivers set off for more than two and a half hours at a time without getting a chance to adjust their tyres. Michelin's ...
Endurance racing, and more particularly the Le Mans 24 Hours, is the only form of motor racing where the drivers set off for more than two and a half hours at a time without getting a chance to adjust their tyres. Michelin's technical staff must consequently be able to anticipate changes in the weather conditions in order to optimise pressures before tyres go on the car.
In Formula 1 and MotoGP, tyre pressures are carefully adjusted before the start, while in rallying the drivers will systematically check their pressures themselves before each stage. At Le Mans, however, the drivers can cover two, three or even more stints at a time - which can mean more than two hours on the track - without doing anything to their tyres, despite the inevitable increase in air pressure as heat builds up inside them. Getting tyre pressures right optimises their efficiency. If the pressure is too high, or too low, performance will suffer. In endurance racing, the art consists in anticipating the ideal pressure as a function of how the temperature is expected to change and only Michelin's technicians are qualified to do this.
The temperature factor
"Tyres are always inflated cold," explains Bernard Jay, endurance tyre developer at Michelin in charge of prototypes, "but we take into account the time at which the tyres will be out on the track and how ground temperatures are likely to evolve. For example, at Le Mans, the tyres that go on for the start are not inflated to the same pressure as those which will be fitted after the first driver/tyre change which is generally early in the evening, and so on. The exact pressures are based on Michelin's years of experience of the French race as well as on work done in testing with our partner teams. We keep records going many years back of all the temperature graphs recorded at Le Mans." After being inflated, the tyres are stocked on special heating racks until their time comes to go on the car. "Just in case the unexpected arises, such as a sudden shift in the weather, we tend to have a full set of intermediate or rain tyres ready that we don't put on the heating racks, just in case--"
Michelin tyres are inflated using dry air. With the exception of certain American events where nitrogen is employed - and even then more by force of habit - tyres are inflated with dried air to prevent moisture from influencing the build up of pressure.