On Saturday, the North American sports car season will draw to a close with the Petit Le Mans, a 10-hour race held at Road Atlanta in Georgia. This year’s Petit Le Mans is also the last race for a fan-favorite class of cars known as GTLM. The category covered Le Mans-legal versions of two-door production cars, which over the years represented a playground for manufacturer-supported programs and some of the world’s best racing drivers.
On the one hand, cutting GTLM is a massive step for the US side of endurance racing, as it ends a direct link between the WeatherTech SportsCar Championship and the annual 24 Hours of Le Mans. But the move also makes the sport a bit less complicated.
“Even some of the most avid car people have a hard time understanding why the red BMW is so much faster than the yellow and blue one or [why] the red, white, and blue Porsche is so much faster than the #9 car or the #16 or the #88,” said John Doonan, president of the International Motor Sports Association (IMSA), the sport’s organizer.
Next year, the IMSA will still have a place for factory teams, but it’s switching to cheaper, more driver-friendly cars with the introduction of a new class, called “GTD-Pro.” Let’s take a look at what’s going on.
The WeatherTech series traces its roots back to the first Petit Le Mans, which was held in 1998. That race adopted the same technical rules used by the Automobile Club de l’Ouest, the organization that runs the annual 24-hour race in Le Mans, France. Among those rules were categories for racing-modified versions of road cars. This is where things get complicated, so bear with me.
Originally, there were two GT classes, called GT1 and GT2. GT1 cars were more highly modified, more powerful, and more expensive to run. They also generated more aerodynamic downforce. Eventually, the category became too expensive and disappeared. GT2 stuck around and was renamed GTE at Le Mans and GTLM in IMSA competition (because having a GT2 class but no GT1 class made too little sense, even for a needlessly complicated sport like endurance racing).
Over the past few years, the same problem that killed GT1 has come for GTLM/GTE. The cars have become more and more specialized; for example, Porsche went to the trouble of making a mid-engined 911 race car. And that has made the vehicles more expensive to campaign, particularly for the privateer teams that are the lifeblood of the sport.
Instead, those privateers largely moved to a different category of production-based sports car called GT3. This category was created specifically with the amateur in mind, even going so far as to mandate driver aids like antilock brakes. Performance differences between various makes of car were adjusted to keep a relatively level playing field (known as “balance of performance,” or BoP), and the result has been full grids at races around the world.
GT3 cars have been racing in the IMSA since 2016 in a class called GTD (the D stands for Daytona, where the IMSA is based and where it starts each racing season). The class is meant for privateer teams with a mix of amateur and professional drivers, and the past few years have seen it boom in popularity. When Saturday’s race starts, there will be 15 cars in GTD and just six in GTLM. (And that’s twice as many GTLMs as raced at the previous couple of rounds.)
So starting next year, the IMSA will add GTD-Pro to the mix. The creation of this separate class for factory teams is an important factor. “We announced the new GT strategy that we’re going to pursue, which I think has lit an additional flame under all the manufacturers that are in GT racing. Now that they understand the direction, they can plan accordingly,” Doonan told me earlier this year.
“You know a company like BMW is already down the path of the new M4, but I think now, when that announcement comes, it gives them a real clear plan to do maybe a factory-supported effort and continue to support customer teams,” Doonan said. “One of the concerns, of course, is they don’t want to race against their customers if they have customer teams. So keeping them separated, if you will, into two categories, is really important.”
“Our hope is that it makes it a bit easier for the fans to understand,” Doonan told me. Part of that effort will involve coming up with a way to separately implement a balance of performance for the GTD-Pro and GTD.
One possibility is to introduce minimum pit stop times for GTD (an approach already used in some amateur classes in other series), although Doonan told me that “there’s other things we can do in sporting regulations to not make some technical brain surgery out of it.” Like GTD, it will use a control tire from Michelin, as opposed to the bespoke tires that Michelin (and others) made for individual GTLM and GTE programs.
“For a couple of seconds of lap time, the delta [between GTLM and GTD] of not only the starting costs, but also having to have all of those spares for two different types of cars—I think for sustainability of the sport, it’s the right thing to do,” explained Patrick Long, a long-time Porsche factory driver who has extensive experience with both Porsche’s GTLM-spec 911 RSR and its GTD-spec 911 GT3 R.
“If it was a delta of GTLM to GT4 [the category below GT3 that is much closer to road-spec], we’d be talking about quite a different sport, but these GT3 cars are serious,” Long said. “The only thing you hope is that with GT3 becoming the new premier GT class, you still have a good representation of pro-am classes and entrants, but it seems like everybody’s aware that formula is doing very well.”
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