Audi has rolled out a long-tail version of its R18 e-tron quattro Le Mans prototype, which it will be using for evaluation purposes in the second road of the 2013 World Endurance Championship, the Spa 6 Hours race in Belgium.

The brand with the four rings will be campaigning three of its R18 prototypes at Spa, the long-tail version seen here as well as two of the regular-length versions.

The long-tail design, which has appeared on famous endurance racers such as the McLaren F1 GTR and Porsche 917, has been shown to be ideal for high-speed racing, particularly on the long straights of Le Mans.

For its long-tail R18, Audi concedes it has optimized the design specifically for the Le Mans track but will be gathering vital data during the Spa race. Engineers will analyze the time differences to be expected between both models on individual track sectors.

Taking turns behind the wheel will be Marc Gené, Lucas di Grassi and Oliver Jarvis.

In a statement, Audi motorsport chief Wolfgang Ullrich said, "Fielding the Le Mans aero variant on the third vehicle that hasn't been optimized for the lap times at Spa is an important element of the preparation for the 24-hour race [at Le Mans].”

The Spa 6 Hours race takes place at Belgium’s historic circuit at Spa Francorchamps on May 4. Meanwhile, the highlight of the WEC, the 24 Hours of Le Mans, takes place on the weekend starting June 22.

All R18 e-tron quattros feature a through-the-road hybrid system that relies on a TDI diesel powering the rear wheels and an electric drive system powering the front pair. Together, they create a pseudo all-wheel-drive system, hence the “quattro” part of the race car’s name.