That’s two different rulebooks to which a manufacturer can build a car for the top category of the series. So on the 16-stong Hypercar entry for Le Mans this year there are nine LMHs and six LMDhs.
LMH stands for Le Mans Hypercar, a rulebook that has been in force in the WEC since 2021. LMDh is new for 2023, but you’ll never see the name written out, it’s not officially an acronym.
But it is easy to guess what the letters mean given that the class was formulated by the Automobile Club de l’Ouest at Le Mans and IMSA based at Daytona in the USA. That little ‘h’ on the end refers to the fact that these cars, like their LMH rivals, incorporate hybrid technology.
The two types of car are very different in some respects, but actually very similar in others.
LMH allows a manufacturer to design and develop its own car from top to tail - or rather from the nose to the tail. That includes all elements of the hybrid system, which, if present, must be on the front axle. It is not mandated: the Toyota, Peugeot and Ferrari LMHs are all four-wheel-drive, but the Glickenhaus and Vanwall are non-hybrid machines that drive only through the rear wheels.
LMDh requires entrants to use a high percentage of off-the-shelf components. What is known as the spine of the car, including the monocoque and the suspension, must be one of the next-generation LMP2 designs from the four licensed constructors, ORECA, Dallara, Ligier and Multimatic.
The rear-axle hybrid system is common to all cars. It’s a combination of parts built by Bosch, Williams Advanced Engineering and Xtrac, who respectively supply the motor generator unit (MGU), the battery and the gearbox. The manufacturer only develops the aerodynamics, supplies the internal combustion element of the powertrain and has the freedom to do what it wants with the electronics.
Source: Autosport