Audi R10-Michelin Project
NEW TYRE DEVELOPMENTThe 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.
"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." Two test sessions with this hybrid Audi R8 were organised.
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. We therefore didn't have any particular concerns on the tyre front," recalls the German driver.
The fruit of experience
"We were extremely surprised by the inaugural tests because they showed us we had been working in right direction. 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," says Matthieu Bonardel. "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."
Concrete examples? The rear tyres of the Porsche GT3s have to withstand considerable loads due to their long rear overhang and high weight. Meanwhile, in touring car racing, a discipline in which Michelin has carved out a particularly successful record, tyres have to cope with extreme conditions, while in the FIA GT Championship the phenomena of wear and durability need addressing. The LMP2 category has been invaluable for us to work on getting tyres up to their ideal working temperature," continues Matthieu. "We quite simply saw that by delving into our past experience, we already had a fair proportion of the answers to the questions raised by the Audi R10 project. And I can say we wouldn't be here today with this diesel prototype if we hadn't had years of experience in the FIA GT championship, in endurance racing and in touring car racing at circuits in Europe, America and Japan. I am extremely proud of the ground we have covered, and this work will help shape the face of endurance racing over the coming years."
Three development phases: safety, durability and performance
When the Audi R10 made its official debut at Sebring at the end of March, a large number of question marks still needed answering. 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. That is to say a safe, reliable construction. Our objective was to run double stints and hopefully not come across any unpleasant surprises," continues Matthieu. 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, for in spite of the extensive test programme the week before Sebring, 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 1½ stints, we needed to tread carefully and manage our tyres," recognises Frank Biela. "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. "Consistency once again involves the tyre's construction, which is the aspect that faces the biggest constraints at Le Mans. Following our most recent tests at Le Castellet, we feel optimistic about the prospect of doing triple stints and, during the Preliminary Test Day, the Audi R10s covered the equivalent of three stints, although with frequent pit stops."
The final phase of the tyre's short term development programme focused on performance."This involved working on the compound and on the front/rear balance. 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," admits Matthieu Bonardel.
The other prototypes benefit
At the end of the Preliminary Test Day for the 2006 Le Mans 24 Hours, the Pescarolo-Michelin team declared that it was very pleased with the new 'Audi' tyres! The wider diameter front tyres developed for the new Audi R10 have 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. "As I've already said, the prototypes have a tendency to understeer and one of the ways to combat this is to run bigger diameter front tyres. However, an increase of 30mm necessitates a high number of other chassis- and aerodynamics-related knock-on modifications."
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 who were at the origin of these new tyres! At Michelin, solutions developed for one partner are consequently made available to all the others in order to ensure equality of treatment.
The Audi R10 was not the only project to keep Michelin's endurance specialists busy in recent months. The new LMP2 Porsche RS Spyders, which are aiming for the endurance title in the USA, have called for the development of a special tyre, as does the new LMGT2 Ferrari F430 whose technical characteristics differ significantly to those of the Porsche 911. And that's not to mention the ongoing tyre development for the GT1 cars!
