Michelin hour six notes

Diesel, rain tyres, and safety cars The six leaders on Michelin tyres The official start to the 75th edition of the 24 Hours of Le Mans was given at 15h00 this afternoon. The 54 cars started off...

                         Diesel, rain tyres, and safety cars

The six leaders on Michelin tyres

The official start to the 75th edition of the 24 Hours of Le Mans was given at 15h00 this afternoon. The 54 cars started off on slicks despite the overcast conditions. It was Audi Michelin # 2 driven by Frank Biela who was leading the race after the first lap after a small error committed by Sebastien Bourdais with his Peugeot Michelin # 8.

A half an hour into the race the three Audi Michelins where running in the top three positions. Then the pit lane ballet commenced have been initiated by Audi who where quickly followed by their tricolour adversaries.

Both the second and third hours were respectively reduced by 15 minutes due to the intervention at two separate occasions of the safety cars. They were brought onto the circuit due to a car stopped at the Ford corner, and then by the violent accident of Audi #3, their young driver's car.

During these numerous slow laps the cars frequently stopped in their stands to put on rain tyres due to the rain showers which were now making regular appearances.

In GT2, the Aston 007 and 009 were leading their category in front of the Corvette #63. The #64 had already retired due to a ruptured transmission. At 18h00, four cars had already officially retired.

Matthieu Bonardel Michelin 4 Wheels Competition Director
"It was a very animated start to the race. During the first hour and a half the teams remained on slicks. Certain teams had chosen soft tyres, but later switched to medium which is in fact a hard tyre.

With the Prototypes, we had planned on a two stints strategy but due to the showers and changes in the tyres it did not allow us to complete even a half a relay. It was obvious that the level of adherence was not great in the early stages of the race. With all the rain fall we experienced yesterday the track is quite `green' and we found ourselves in conditions of over steer like in qualifying on Wednesday night. Although the circuit is slippery, our tyres have done what was required of them, and did not suffer any particular degradation. The pace became more regular when the rains started again. We are at the maximum alert at our tyres facilities with these non stop changes. "

The importance of multiple-stinting at Le Mans

At Le Mans, tyre changes are relatively costly time-wise and teams tend to prefer to cover more than one stint with the same set of tyres. Durability or more accurately 'durable constant performance' is consequently one of the keys to Michelin's lasting success at Le Mans where its tyres have gone unbeaten since 1998.

The regulations specify that just four mechanics may work on the cars in the pit-lane at any one time, and the number of nut-guns is also restricted to just two. Meanwhile, tyres may only be changed once refuelling has been completed.

As a result, tyre changes are particularly costly time-wise, so the objective is to cover as many stints as possible on the same set of tyres without compromising either safety or performance.

A decisive advantage beyond 1,000km

In the opinion of Matthieu Bonardel, Michelin Competitions manager of 4-wheel activities, Michelin tyres offer a decisive advantage when the total race distance exceeds 1,000km: "A 1,000km race represents four or five stints, that is to say twice the number of opportunities not to change tyres and therefore a potential time saving of two times 12 seconds. In an event that lasts more than three hours, it is practically impossible to imagine a prototype with serious hopes of victory not having the capacity to cover more than one stint at a time."

Tactics

That said, just as car and tyre performance has progressed over the years, so has the efficiency of the pit crews. Although there is little that can be done to save time when refuelling the cars (the rate of flow of fuel into the tank is set by the regulations), the mechanics have become increasingly proficient over the years when it comes to changing tyres.

As recently as five years ago, this job used to take between 20 and 25 seconds. Today, the time required by many teams has been slashed by half, and 12 seconds is currently more the norm. As a result, the time that can theoretically be saved by covering more than one stint with the same tyres has come down too.

Indeed, switching to a more competitive tyre that only gives its best during a single stint may now be preferable if the gain achieved by staying on the same tyres is less than 6 seconds per stint, which works out at approximately 2/10ths of a second per lap.

In the case of the prototypes, the tactic is still likely to pay. The decision is more borderline for the GT1 runners, however, because the gain represented by switching to a softer compound works out at between 2 and 3 tenths per lap. In GT2, it is the drivers themselves who tend not to want to double stint with the same tyres since their cars carry higher fuel loads.

-credit: michelin

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About this article
Series Le Mans
Drivers Frank Biela , Sébastien Bourdais