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MICHELIN AT NIGHT: BEARING UNDER THE PRESSUR OF LEADING 4 CATEGORIES Night time slowly settled over the mythic Sarthe circuit brining with it little change in the 75th 24 Hours of Le Mans race positions. At 21h57 following an accident in ...


Night time slowly settled over the mythic Sarthe circuit brining with it little change in the 75th 24 Hours of Le Mans race positions.

At 21h57 following an accident in which only the official Corvette managed to escape, Audi # 1 stopped for 4 minutes in the pits in order to change its bonnet and rear wing, stopping once again on the following lap to fix pour a poorly connected headlight. These two stops were not too penalising however as they both were executed while the safety car was out on the circuit.

The green flag was waved at 22h23.

Pescarolo #17 suffered an oil leak about the same which proved more difficult to resolve and the Prototype did not regain the race until 23h28.

10 more cars retired as of 1h00 this morning.

There was a change in the leader of category LMP2 with the Courage AER #24 taking over, however the situation remained unchanged in LM GT1, and LM GT2.

Matthieu Bonardel Michelin 4 Wheels Competition Director "The temperatures have not yet dropped very much. Some teams have come in to switch to mediums as they were very pleased with their performance and adherence. The major change in temperature will be around 2h00 this morning. We will be increasing the pressure as we predict that the tyres are going to get cold and the ground more humid. We need to anticipate the tyre conditions for those who have gone out on mediums for three stints.

This is precisely what the Michelin technicians will be concentrating on and amplifying throughout the night. We will do the reverse however in the morning. Certain cars will have done three complete stints without any problems. Sebastien Boudais with his Peugeot-Michelin just signed off the fastest lap during his third stint.

There is also good news coming from the GTs, with Aston Martins and Corvettes on double stints. The Porsche and Ferrari in GT2 are also running two stints without difficulty where as in previous years it was a bit trickier. The coldest part of the evening will hit us at about 6h00 this morning and the cars will be on soft tyres. Around 10h00 we will start to use the mediums again so that at around 12h00 no one will be on a overly tender tyre that might affect their performance. "

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 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. Rally drivers, racing drivers and MotoGP bikers pay far more attention to the tyre pressures of their respective machines than ordinary motorists do with their own car. For the former, you could even say it was an obsession and when it comes to 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..."

Dry air

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

-credit: michelin

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Series Le Mans