What is LMDh and why are we so excited about sports car racing in 2023?

A sketch of the Porsche LMDh race car
Enlarge / This sketch is all we’ve seen of Porsche’s forthcoming LMDh hybrid racer. But now we know that when it starts racing in 2023, it will be run by Team Penske.


In 2021, there is a real buzz building in the world of sports car racing. After many years of running incompatible technical regulations, the three organizations that are in charge of endurance racing in the US, France, and the rest of the world have managed to find common ground. Soon, a car that’s able to compete for the overall win at Le Mans will also be eligible to do the same at Sebring or Daytona, and vice-versa.

This convergence was meant to stimulate interest and draw in new entries, and it’s doing just that: Acura, Audi, BMW, Ferrari, Glickenhaus, Peugeot, and Toyota have all confirmed programs. Entries are also expected from Cadillac, Hyundai, and Lamborghini. That level of manufacturer involvement hasn’t been seen since the glory days of Group C, and it’s fair to say the increasing field of competitors has fans excited at the prospect.

But sports car racing—which often involves multiple classes of cars racing at the same time—is nothing if not overly complicated. The news is good, but bear with us as we explain what’s going on.

Prepare for acronyms: IMSA, ACO, FIA, WTF

To start with, there are three different organizations involved in the regulations and decision-making. Here in the US, the International Motor Sports Association (IMSA) is in charge of overall sports car racing and the Weathertech SportsCar Championship, which includes specific events like the Rolex 24 at Daytona, the 12 Hours of Sebring, and the Petit Le Mans, among others.

Over in Europe, the Automobile Club de l’Ouest (ACO) is the organizer of the 24 Hours of Le Mans. And then there’s the Fédération Internationale de l’Automobile (FIA), which is in charge of global motorsport and world championships like the World Endurance Championship.

In the 2000s, IMSA and the ACO used very similar technical regulations. But in 2014, IMSA merged with another US series, and that new collaboration had to come up with an original rulebook to accommodate a new mix of cars. Unfortunately, what they settled on left no room for the very fastest Le Mans prototypes (called LMP1s).

LMP1h, DPi

The mighty LMP1s continued to race at Le Mans and in the WEC, eventually evolving into some of the most technologically advanced cars ever seen. LMP1 soon turned into LMP1h—”h” for hybrid. A complicated set of rules called the Equivalence of Performance was put in place to theoretically allow different technical approaches to compete on a level playing field. In the resulting races, we saw kinetic flywheels and supercapacitors as well as lithium-ion batteries, both gasoline and diesel engines, and rear- or all-wheel drive powertrains.

For a few short years, fans were treated to some epic racing between Audi, Toyota, and Porsche. But the two German OEMs had Formula 1-sized budgets that became unsustainable, particularly in the aftermath of dieselgate. By 2018, only Toyota remained, competing against non-hybrid privateer LMP1 cars. The ACO tried to make things fair for the much less well-funded privateers through an ever-increasing handicap, but such regulations didn’t always succeed.

Meanwhile back in the States: in 2017, IMSA introduced its new DPi (Daytona Prototype International) category. This took the ACO’s second-fastest category (called LMP2) as its starting point, but where LMP2 was aimed at privateer teams and amateur drivers, DPi was for OEMs and factory teams. So, IMSA allowed DPi entrants the freedom to choose their own engine and develop their own electronics (both of which were spec items in LMP2). The new DPi guidelines also gave the OEMs more styling freedom so that the racing prototypes looked a little bit more like actual road cars.

Technical regulations don’t last forever, of course. IMSA, the ACO, and the FIA all knew attracting more OEMs to the top class of sports cars would ultimately require a few things. First, the rules had to allow for some form of hybridization, given almost every company’s move to electrify passenger car fleets. Next, the cars should bear more resemblance to road-going cars. And finally, costs needed to become sensible.

LMH, LMDh—it’s all hypercar to me

Enter the hypercar. The ACO got the ball rolling first, announcing that it wanted to attract racing versions of road-legal hypercars like the Aston Martin Valkyrie. There’s something romantic about the idea of taking off a car’s number plates, putting in a rollcage, and going racing (even if it’s been about 50 years since such a thing was really practical).

So the ACO created a Le Mans Hypercar (LMH) category to make that happen. LMH allows entrants quite a lot of technical freedom (though less than LMP1h); the cars are heavier and less powerful than LMP1, with a lower downforce-to-drag ratio of 4:1. The first LMH cars took to the track this year, including a pair of Toyota GR010 hybrids, a pair of Glickenhaus 007 hypercars, and an Alpine LMP1 car that has been grandfathered in. As we reported recently, Peugeot is set to return next year with its 9X8 hybrid, and Ferrari has confirmed it will enter LMH in 2023 with a hybrid car.

Still, IMSA had some of its own requirements that meant it couldn’t just adopt LMH for its top class. But DPi proved pretty successful, and so in 2023 IMSA is evolving that category into a new one called LMDh. Like DPi, it starts off with an OEM choosing one of four approved “spines”—the carbon fiber chassis manufactured by Dallara, Ligier, Multimatic, and Oreca. As with DPi, each OEM is free to choose its own engine and electronics, and there is even more styling freedom than DPi, albeit with the same 4:1 downforce-drag ratio as LMH.

There are plenty of spec(ified) components that will be identical in each car to keep costs down. That includes the hybrid system, which combines a Bosch electric motor and Xtrac sequential gearbox, as well as a lithium-ion traction battery from Williams Advanced Engineering. Total power output will be capped at 670 hp (500 kW) sent to the rear wheels—the electric motor is allowed to regenerate at up to 268 hp (200 kW) but can only deploy 67 hp (50 kW).

Fans of uninhibited technology development may turn their noses up at the use of spec components, and it certainly complicates any stories an OEM might want to tell about technology transfer from the race track to road cars. But the upside is the price tag—the complete hybrid system will cost around $355,000 (€300,000) and the chassis about $408,000 (€345,000). Add in the cost of the internal combustion engine and some other bits, and a complete LMDh car should still cost less than $1.5 million.

That’s definitely attractive for an OEM like Audi. “The new hypercars fit perfectly with our new set-up in motorsport and our roadmap of electrification,” an Audi Sport spokesperson told Ars by email. “The regulations for LMDh cars in particular allow us to field fascinating race cars in prestigious races worldwide while regulations are trimmed for maximum cost efficiency.” (Audi and Porsche are working together on an LMDh program using the same engine and the same Multimatic chassis but with different styling, which may also result in a Lamborghini version in 2024.)

The fact that the LMDh is allowed in US championships also factored in to some OEM decisions. “We know what engine we’re going to put [in], we know what constructor we’re going to work with, and then the program is in the first place centered around the IMSA championship because we want to have this for our biggest market, which is the US,” said BMW Motorsport boss Mike Wrack. (BMW is believed to have selected Dallara as its chassis-maker.)

When asked, Wrack didn’t see much wrong with the use of spec components. “You see it also in Formula E: there is a lot of spec, but there are also some open areas. And we learned a lot there,” he said. “So yes, there is a lot of spec, but I think the spec is the only way to keep costs under control. And with hypercar [LMH], there is an element of additional cost, which in current times, it’s really difficult to get through [the board of directors]. So, for us, the LMDh was a preferred direction, not only because of cost efficiency, but also because of the US market.”

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