The organisers of this weekend's Le Mans 24 Hours have deemed the Audi R15s legal, following a protest from chief rivals Peugeot.
Peugeot had protested a number of pieces of bodywork on the Audi R10, the successor to the all-conquering R10, saying they weren't within the regulations.
According to the rules, it is illegal for elements of the bodywork on a Le Mans car to be specifically designed for the sole purpose of producing downforce, and after seeing the Audi car in action, Peugeot believed them to be in breach of this rule.
Peugeot is now appealing to the FIA, which means this year's race result is likely to be clouded by controversy.
The Audis set the pace in Wednesday's practice session, where the fastest times were set early in the morning as the rest of the day was rain swept.
Last year's winning crew of Allan McNish, Tom Kristensen and Rinaldo Capello posted the quickest time of the session, but just half a tenth quicker than their team-mates Lucas Luhr, Mike Rockenfeller and Marco Werner