At the beginning of the 21st century, Audi set the benchmark in endurance racing. With the iconic Audi R8, the German manufacturer dominated the LMP900 category and later LMP1, claiming no fewer than five victories at the 24 Hours of Le Mans. In 2006, Audi raised the bar once again with a revolutionary successor: the Audi R10 TDI. An LMP1 prototype powered by a diesel engine, something previously considered unthinkable at the highest level of motorsport.

The R10 TDI proved to be another masterstroke. Audi enjoyed success on both sides of the Atlantic, but serious competition was on the horizon. Peugeot entered the fray with the 908 HDI FAP, also diesel-powered. While the French challenger often held the edge in outright pace, Audi could rely on legendary German reliability. The result was a series of fascinating battles that pushed both manufacturers to their absolute limits.

To stay competitive, Audi developed the R15 TDI as the successor to the R10. That, however, did not mark the end of the R10’s career. In 2009, Kolles Racing — the team led by former Formula One team principal Colin Kolles — switched to sports car racing and acquired the now-surplus Audi R10 TDI machines.

We recently spoke with Charles Zwolsman, one of the drivers who competed in the full Le Mans Series season and the 24 Hours of Le Mans in 2009 with Kolles Racing’s Audi R10 TDI. I was there in 2009 as well, attending Le Mans for the first time with a camera in hand.

Debuting with a proven champion

With three American Le Mans Series titles, one European Le Mans Series title and three Le Mans victories in just three years, the Audi R10 TDI had more than proven its credentials. By 2009, however, it was no longer the newest or fastest car on the grid.

What was it like to debut as a customer team with an ageing, yet highly successful prototype?

“We knew the cars from other manufacturers would be quicker,” Zwolsman explains in an exclusive interview with GT REPORT.

“That’s when it’s reassuring to be able to rely on the proven reliability of the R10 TDI.”

That reliability paid off immediately. In qualifying for the 24 Hours of Le Mans, both Kolles Racing cars secured 13th and 14th on the starting grid. A solid result for a customer team.

Panic before the start

The 24 Hours of Le Mans is an extreme test for both man and machine, traditionally contested by three drivers per car. In the Audi wearing start number 14, former Formula One driver Narain Karthikeyan was set to take the start. Disaster struck just moments before the race.

While jumping over the pit wall, Karthikeyan dislocated his shoulder. The ACO deemed him unfit to race, leaving Charles Zwolsman and André Lotterer to complete the full 24 hours as a duo.

“That was a real shock,” Zwolsman recalls.

“I was sitting with the team, ready to watch the start, when team manager Boris Bermes burst in and shouted: ‘Charles, put your helmet on — you’re starting!’ At first I thought he was joking, but before I knew it I was strapped into the car and heading out for the formation lap.”

There was no time to process what had happened.

“The race just flew by. André and I finished the 24 hours purely on adrenaline.”

Still, Zwolsman emphasises the disappointment for his teammate.

“I felt especially sorry for Narain. He was about to become the first Indian driver to compete at Le Mans. He was a great teammate and a great person, and I really wished he could have raced with us. In hindsight, it’s a remarkable story, but at the time it was tough.”

The rise of a Le Mans legend

For both Zwolsman and Lotterer, Le Mans 2009 marked their debut at the iconic race. For Lotterer, it would prove to be a defining moment in his career. His performance earned him a promotion to Audi Sport Team Joest, where he developed into one of endurance racing’s greats and a three-time Le Mans winner.

Zwolsman, however, had known Lotterer long before.

“I knew André from karting. He raced against my younger brother, Ross. Even back then, you could tell he was something special.”

What stood out most was how quickly Lotterer adapted to the Audi R10.

“He barely needed any time to get used to the car. What impressed me most was how quickly he was able to attack the Porsche Curves right on the limit.”

That was no small feat.

“It’s a huge risk during a weekend like Le Mans. You don’t want to make a mistake, especially in a car that’s completely different from a GT.”

Racing with a diesel powerhouse

What truly set the Audi R10 TDI apart was its engine: a 5.5-litre V12 turbodiesel delivering immense torque.

“Fortunately, it felt natural quite quickly,” says Zwolsman.

“The engine runs at low revs, so you have to upshift much earlier. But the biggest difference is the sensation.”

Compared to a screaming petrol engine, the diesel was almost eerily calm.

“At high speed on the straights, all you could hear was the wind. To stay focused, I sometimes had to literally talk to myself: ‘Come on, we’re racing.’”

Audi Sport provided strong technical backing throughout the event.

“We had two engineers from Audi monitoring the engine during the race. The support from Audi Sport was outstanding.”

Reliability to the finish

Despite the dramatic circumstances and the physical challenge of running with just two drivers, the Audi R10 TDI once again proved its legendary reliability. A gearbox issue during the night caused a delay of around thirteen minutes, but the car kept running and steadily climbed the order.

After 24 demanding hours, the #14 Audi crossed the line seventh overall.

Remarkably, this remains Team Kolles’ best-ever Le Mans result. In the years that followed, the team would return to Le Mans ten more times under various names — without ever seeing the chequered flag again.

How does Zwolsman feel about still holding that record?

“Mixed feelings,” he admits.

“In later years there were smaller and less competitive LMP1 fields, so the opportunities were definitely there to improve on that result.”

Nevertheless, his respect for the team remains clear.

“The team went on to develop their own cars and took on factory teams. That deserves huge respect. You really want them to succeed.”

He concludes with a smile:

“But at the same time, Team Kolles, André and I can still be very proud of what we achieved in 2009.”