The 2015 Petit Le Mans overall race win by Porsche North America’s Patrick Pilet and Nick Tandy aboard a GTLM class Porsche 911 RSR was a perfect demonstration of Michelin technology in competition.
It is also unlikely to happen again in the IMSA WeatherTech Sportscar Championship for many years.
IMSA officials collect and analyze an extraordinary amount of data to set the technical limits and maintain competition within each class and create a stratification of the four classes in the WeatherTech Championship.
While teams and manufacturers often grumble about the measures within their respective classes, the stratification from class-to-class is also a delicate balance, as cars in each achieve lap times in different fashion. As IMSA’s Geoff Carter told Michelin Alley earlier this year:
“We are a multi-class series,” he said. “From a car standpoint, we have two Prototype classes and two GT classes. From a driver standpoint, we have two ‘Pro/Pro’ classes and two ‘Pro/Am’ classes. It’s like a 3D chess board in terms of how to manage the interactions.
“We try to have 4 percent stratifications between each class. We often see less than that, somewhere between 2.8 and 3.5 percent.”
The measures are based upon Pro drivers running in dry conditions.
At Road Atlanta in 2015, the Prototypes were expected to lap in the 75-76 second range and be 2-3 seconds a lap quicker than the PCs, with the GTLM cars another 2-3 seconds back.
In Thursday’s dry Practice 1 at Road Atlanta, the best P time was 1:15.163 and the timing delta from P to GTLM was 4.3 seconds. As teams shifted plans and prepared for a likely wet race, Practice 2 saw a best P class lap of 1:16.937, a 2.7 second delta.
IMSA utilizes two measures to help maintain class stratification and pit road safety. The first is to separate the grid into two starting fields, one for the Prototype and PC classes and a second, typically 30 second later, for the GTLM and GTD classes.
In the Pro-Am based PC class, Pros typically run at or near the IMSA projections, but it is often the “Am” or lesser designated driver starting the race.
Depending on the circuit, their lap times are often slightly slower or less consistent than those of the factory shoes aboard the GTLM machines.
Pass and Re-Pass
The second, and more impactful measure, has the Prototype and PCs pit on the first lap that the pits are open, with GTLM and GTD cars pitting on the following lap.
In the process, all of the Prototypes, including cars that had been passed or were several laps down, end up ahead of the GT field on each restart.
The No. 911 Porsche of Pilet and Tandy sat 35th in the 37 car field on the starting grid after a qualifying infraction. Ahead were 18 GT entries. They would all start 30 seconds behind the 16 Prototype and Prototype Challenge class entries.
Tandy was 21st at the end of lap 2 and 10th overall on lap 9. He moved into 5th overall at lap 16 and led the race on lap 35 when the Prototypes pitted under caution.
He was not alone at the front. Fitted with the Michelin wet tires developed for Le Mans and the WEC championship, the GTLM class BMWs, Corvettes and Risi Ferrari had also carved through most of the Prototype field.
Those gains were however negated by five safety car cautions to reset the field in the first 93 laps. Each restart placed the GTLM cars behind the PC and P entries and required that they pass them in the wet once again.
GTLMs to the Lead
Taking advantage of a long green flag run from laps 106 to 138, the No. 4 Corvette took the overall race lead on lap 125, joined at the front by the No. 3 Corvette, No. 24 BMW and the No. 911 Porsche which led until lap 151.
At this stage of the race, the Michelin teams were not only taking back that 4-5 seconds per lap of IMSA stratification, they were as much as 2-3 seconds per lap quicker than the Prototypes, making a total difference of 6-8 seconds.
As the rain increased and track conditions declined, IMSA officials red flagged the race for one hour and five minutes at lap 163.
Playing the End Game
When the red flag was withdrawn and the field took to the track on lap 164 under the safety car, the Action Express Corvette DP team split its strategies, pitting the No. 5 and leaving the No. 31 car out to lead the field.
The 911 Porsche also pitted and rejoined the field in 8th place overall.
Tandy was 4th on lap 168 and up to 2nd on lap 180 as he reeled in the race leader. He made his move in turn one of lap 188.
For the Win
“Nick Tandy’s pass of the lead Prototype on the outside in the wet at turn one 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.”
With Tandy pulling away, the No. 31 Action Express entry pitted on lap 193, as the No 24 BMW GTLM took over 2nd place.
Track conditions were deteriorating when a full course yellow appeared on lap 194. It was clear that the Prototypes were not going to catch the leading GTLMs.
IMSA officials had little choice but to call the race on lap 199 after 7 hours and 51 minutes.
While the fans and GTLM teams enjoyed the upset, the GTLM overall race winning performance was not universally well received by IMSA and its Prototype and PC teams. Greater restrictions have subsequently been placed on GTLM wet tires, making a repeat performance increasingly unlikely.
***The two Porsche North America Porsche GTLMs qualified 1-2 overall in the wet qualifying session for the 2016 WeatherTech Championship season opening Rolex 24 At Daytona.
***IMSA officials declined a request to allow the two Porsches to lead the ceremonial first parade lap, then drop to the outside and take up their positions at the front of the GT field for the race start.
***Following the 2016 Sebring race, IMSA decreed that the practice of “cutting” or deepening the treaded groove pattern on wet tires to evacuate more water in heavy wet conditions would no longer be permitted in any class in the WeatherTech Series, including the “open-tire” GTLM class.