The Audi R10-Michelin Project
A technological challenge

At 5pm on Saturday June 17 2006, a diesel powered car will line up for the start of the world's most famous endurance race, the Le Mans 24 Hours. Although this competition has already been the scene of trials with other fuels than petrol in the past, this is the first time this type of project has been undertaken by a major motor manufacturer. A diesel engine could well win this year's event and Audi has chosen Michelin to joinit for this demanding technological challenge.

The decision to switch to diesel power 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. In all couples, an ability to 'talk' is essential. In this case, however, it is 'torque' that has been the major topic of conversation. Yet more than ever the true challenge for tyres in this discipline is their ability to cope with the bigger constraints at higher speeds over longer distances. The forces to which they are exposed are as intense as those faced in Formula 1, yet Le Mans tyres need to last for the equivalent of three Grands Prix!

"Engine torque? That, we can handle," affirms Michelin Competition's Circuit Racing Programme Manager Matthieu Bonardel in answer to the commonly held belief that has been doing the rounds in endurance circles since the official announcement of the R10's new V12 diesel engine's maximum torque, namely 1,100Nm. "If only that was the only problem we faced--"

The technical characteristics of the Audi R10 have effectively had a knock-on effect concerning tyres on several fronts. To begin with, the block of the R10 is heavier than that of the V8. The weight split is different too and there is more weight on the rear tyres. There's the endurance factor too, 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% 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. High torque is a challenge for the drive train, but not necessarily for the tyres," insists Matthieu Bonardel.

New-- front 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. 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 which change a great deal.

The men from Michelin have been working on the Audi R10 project for three years now. "Audi's management took us into their confidence at the 2003 Le Mans 24 Hours," reveals Matthieu Bonardel. "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.