with its latest challenger, its third car in as many years; the R18 TDI.
Reduced capacity New engine regulations reduced capacity for diesel engines from a 5.5-litre maximum to 3.7-litres, and the resulting loss in torque and power meant teams had to produce slippery body shapes to maintain top speed. ‘Obviously, with a change in the rules, especially with the engine size and the reduction of power available, the aerodynamic efficiency has become more and more critical,’ says Audi’s technical director, Ralf Juttner. ‘Parallel to that, there have been some rule changes in the last few years which have changed the balance between the pros and the cons of open or closed cars, and that made us take the opinion that closed was the right way to go.’ Dr Wolfgang Ullrich, head of Audi’s Motorsport division
since 1993, was a firm advocate of the open design, with its increased appeal to American audiences who could easily identify a driver, and the faster driver changes during the pit stops. With information from the Bentley programme in 2001-
2003, it re-affirmed Ullrich’s belief in the open car. However, Audi pulled out of the ALMS after the 2008 season, and new tyre changing regulations reduced the
“we will do well to get between 30 and 60% overall elastic roll resistence from the bars”
emphasis on fast driver changes. By the time the new engine regulations were
announced for 2011, even he had to concede that closed was better: ‘About one and a half years ago, we put a bubble over the cockpit of the R15 and put it in the wind tunnel. The result was clear. It was going to be better, so we knew we had to make its successor a closed car.’
These front end plates also shifted the balance forwards, but knocked more counts of downforce off the rear than they added to the front. Drag did reduce a little though
Testing times The car rolled out for the first time at the end of November 2011, four months after the Peugeot 908 had its first track test, and since then testing has been both extensive and thorough. From the outset, the Audi R18 has given the team the speed needed to compete with Peugeot, and for the drivers, the confidence to constantly push to find the limits. ‘If out of the box, the lap times are quick, you know that
it is a good car,’ says driver Romain Dumas, ‘[but] if out of the box you are missing two seconds, you have to find a set up to find that time. This car had a first roll out and was already quick, and there is still a lot to go.’ By producing a closed car, the drag figures immediately
improved over the open-cockpit R15, and the reduction in downforce has not been a major factor in the performance of the car. Through the Porsche Curves, and through Eau Rouge, the car is planted, solid and stable. ‘You have got to have a balance,’ says driver Allan
McNish. ‘When you have balanced aero, if you take aero off you have the same balance, but less grip. The worst thing, whether in high or low aero spec, is if the car is imbalanced, then you will be slow.’ With less grip, the tyre characteristics are different,
and at the Spa 6-hours the difference between Audi and Peugeot was startling. Audi had a big problem with the pick up going off line to pass the slower cars, to the extent that Benoit Treluyer had a hole punched through the wheel arch of his car, and the Peugeot was simply better in the second stint on the same set of medium compound tyres. As a result, Audi went away to re-think its strategy.
Weight reduction Audi has worked hard on reducing the base weight of the car. The carbon body is made in one piece, instead of upper and lower sections glued together, which makes it torsionally stiffer. The chassis is rumoured to weigh just 72kg, lighter than the R15 chassis despite the addition of a roof, windscreen and doors, and the entire base weight of the car is a quoted 850kg. That is a base weight that Audi has campaigned for the ACO to adopt for non-hybrid cars, rather than a blanket 900kg limit whether an energy recovery system is run or not, though the ACO rejected that plan this year. This weight reduction comes at a time when Audi’s production cars are also on a diet. The latest A6 is 80kg
www.racecarengineering.com • August 2011 79
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