On a rain-soaked day at Road Atlanta in 2015, Porsche pulled off one of the biggest upsets in the modern era of sports car racing, with Nick Tandy and Patrick Pilet driving their GT Le Mans class car to the overall win at Petit Le Mans.

The weather-shortened race played into the advantage of Michelin’s technical partner teams, which took six of the top 10 finishing positions overall, and remarkably all being GTLM entries, typically as the third slowest class.

Tandy and Pilet, who were due to share their No. 911 Porsche 911 RSR with Richard Lietz, endured through a near-record ten full-course cautions, despite having started from the rear of the 37-car field due to a technical violation.

The Englishman was up to 10th overall by Lap 9 and into the top-five just seven laps later, and remained in the hunt throughout the first half of the race.

While a one-hour-long red flag for track conditions halted proceedings, Tandy’s magic driving, on Michelin’s WEC specification wet weather tires, in the 8th hour saw him pass the No. 31 Action Express Racing Corvette DP of Eric Curran for the overall lead.

“Nick Tandy’s pass of the lead Prototype on the outside in the wet at Turn 1 in the dark, was an example of total commitment,” said Chris Baker, motorsports director, Michelin North America.

“Having caught the Prototype, he was not going to be denied. That was a truly great pass.”

He then managed to bridge out a gap of anywhere from three to six seconds per lap over the Prototype, prior to full-course yellow on Lap 193, with the race being called early after 7 hours and 51 minutes.

“Honestly the last stint I did in the car, when the rain was pouring down, was the hardest stint I’ve ever had in my life and it’s the most concentration I’ve ever had to put into driving a race car,” Tandy said afterwards.

It marked the first multi-class overall victory for Michelin in the post-merger world of the WeatherTech SportsCar Championship and a unique Le Mans-Petit Le Mans double for Tandy, achieved in the span of just four months.

While Tandy’s Porsche 919 Hybrid was among the LMP1 cars that were expected to fight for overall honors at Le Mans, not many had expected a GT car to ever claim an outright victory in a major endurance race.

And measures have since been put in place to help prevent it from happening again.

IMSA adjusted the GTLM tire regulations in 2016 to prohibit the practice of “cutting” or deepening treads on wet tires, and eventually required teams to homologate slick tire constructions and compounds prior to the start of each season.

With the entire GTLM field on Michelin tires, and cutting and deepening treads no longer allowed, Michelin and its teams agreed to race on a “non-confidential” or customer racing wet tires that proved very effective at the 2017 Rolex 24 at Daytona.