The Audi R10 - a 'tyre-ing' project.

On Saturday 17 June, Audi will become the first major manufacturer to launch an assault on the Le Mans 24 Hours with a diesel powered car - and Michelin will play an important role in trying to help the R10 follow in the footsteps of the ultra successful R8.

The decision to switch to diesel power with the R10 is not only a bold gamble for Audi, it has also been a significant challenge for Michelin whose tyres have taken the German carmaker to victory at Le Mans on five occasions since 2000.

The extra torque of the diesel powered R10 has been the topic of much conversation heading into the most famous endurance race of them all, although the true challenge for tyres this coming weekend at La Sarthe will continue to be dealing with the constraints of running at forces equal to those experienced in Formula One for the equivalent of three Grands Prix...

"Engine torque? That, we can handle," Michelin Competition's circuit racing programme
manager Matthieu Bonardel said regarding the torque situation with the R10. "If only that was the only problem we faced..."

The technical characteristics of the Audi R10 have understandably had a knock-on effect concerning tyres on several fronts.

For a start, the block of the R10 is heavier than that of the V8, and the weight split is also different - meaning there is more weight on the rear tyres. The endurance factor then comes into play, since it is safe to presume that the drivers will put in longer stints, which means the tyres will cover longer distances. And with a maximum power of 650hp, the TDi engine is also something like 15 per cent more powerful than the former FSi block, so this too will make bigger demands on the tyres. Finally, there's the torque...

"But torque is not a problem if the vertical load is applied correctly onto the tyres, that is to say if the aerodynamics are well honed and if the traction control system is optimised," Bonardel insists. "High torque is a challenge for the drive train, but not necessarily for the tyres."

Ironically, to combat wheelspin of the rear wheels, Michelin's developers have worked on the front tyres.

"Torque is effectively ten times higher under high speed braking because of aerodynamic downforce," Bonardel continues. "However, the phenomenon of weight transfer means it's the front tyres that suffer the most. At the same time, the prototypes have a tendency to understeer. So, to optimise the balance of the car and to provide additional grip, we have increased the diameter of the front tyres by 30mm."

Three centimetres doesn't sound like much - but it will change a great deal.

The men from Michelin have been working on the Audi R10 project for three years now, with this years race the moment when both parties hope the work carried out will yield results.

"Audi's management took us into their confidence at the 2003 Le Mans 24 Hours," Bonardel said. "We were told the key features of the project - namely the type of vehicle, its technical characteristics and their impact on the tyres - so that we could begin computer-assisted simulation and calculation work.

"In 2004, we went testing with a 'hybrid' Audi R8 that featured certain elements of the future R10 - such as the wheel arch dimensions, the ride height and weight distribution. This enabled us to produce a range of tyres adapted to the constraints involved and to begin testing at Jerez."

Testing with the R10 itself began on November 29, 2005 at Mizano, in Italy, with Frank Biela at the wheel.

"Tyre-wise, the objective of the session wasn't to maximise the tyres' performance or durability, but more to see if there were any basic problems," the German recalled. "We therefore didn't have any particular concerns on the tyre front."

"We were extremely surprised by the inaugural tests because they showed us we had been working in right direction," Bonardel added. "The chemists, calculations staff, developers and technicians had been working 'blind' for two years.

"For me, the development of the Audi R10 tyres is the fruit of Michelin's long experience of endurance racing. We analysed all the constraints that endurance tyres face in all the different categories in which we have been involved. On the one hand, we noted all the technical constraints relating to the Audi R10. On the other, we had a number of solutions in stock to cope with them."

When the Audi R10 made its official debut at Sebring at the end of March, a large number of question marks still remained. Test work carried out at the beginning of January in Florida enabled the initial work that needed to be done to be identified, but it was still necessary to tread cautiously.

"We consciously favoured a cautious approach to the car's maiden race," the programme manager continued. "That is to say a safe, reliable construction. Our objective was to run double stints and hopefully not come across any unpleasant surprises."

This 'safe' method enabled the Audi R10 to go on and win the race...

In the early part of the endurance season's opener, Michelin's engineers and developers were somewhat on their guards however, as none of the drivers had spent all that much time at the wheel, so the feedback of information was quite limited.

"We knew that after forty or so laps, which is equivalent to one and a half stints, we needed to tread carefully and manage our tyres," Biela said. "The final part of the second stints was rather delicate, but we made it, at a tough circuit like Sebring, and at the hottest moment of the day too! Bravo, Michelin!"

Once the 'safety' phase had been mastered, the next step of the tyre's development was to work on consistency with the aim of triple stinting at Le Mans - a test at Le Castellet leaving the team optimistic that that will be possible. From there, the final phase of the short term development was focused on performance.

"This involved working on the compound and on the front/rear balance," Bonardel said. "The Audi R10 qualified on pole position at Sebring so we are not unduly concerned regarding Le Mans. The lion's share of our work will in fact begin after Le Mans as we look ahead to 2006 and 2007. Then we will take a fresh look at consistency, etc. We are not quite so serene as far as the qualifying and rain tyres go however. It is always difficult to work on those. The Audi R10 has run very little in the wet to date."

While Michelin have worked hard on getting the product right for the R10, Audi aren't the only team likely to benefit from the extensive work that has been going on ahead of the race, with the wider diameter front tyres developed for the new Audi R10 having effectively been made available to Michelin's other LMP1 partners.

Some, like Pescarolo, took up the offer, while others - like Swiss Spirit - preferred to stay with their usual tyres. The new tyres were tested on the Pescarolo-Judd at Le Castellet at the end of March before the team reverted to the original dimension for the first two rounds of the Le Mans Series. However, the French team will be back on the new tyres at Le Mans where the Pescarolo-Judds will be directly opposed with the Audi R10s that were directly behind the tyres being developed in the first place.

Who makes the most of their tyres in the race itself, remains to be seen...