The thorny issue of performance balancing continues to evolve in 2024 as the IMSA organisation, which runs the IMSA Sportscar Championship in the US, has taken a completely new approach to balancing its GTD category cars.
GTD is the name IMSA gives to its arena for GT3 vehicles and is split into two classes: GTD Pro for all-professional driver lineups and GTD for pro-am crews.
GT3 cars race in various series around the world, and all have to fit within performance windows set by the FIA, which owns the intellectual property for the category. These performance windows balance lift, drag and power, and the combination of these elements brings the cars to a reasonable level of competition with each other.
Given that the racecars come from production models, there are vast differences between them in terms of concept, which then leads to different behaviour on track, and so a system is needed to balance the cars within these performance windows.
Fortunately, with so many cars out on track, there is a mountain of data from which to work, but subtle differences between the various championships makes life more complicated, and the sanctioning bodies have each had to adopt their own method of working.
Model behaviour
IMSA’s model is developed in conjunction with the FIA, which governs the GT World Cup in Macau, and the World Endurance Championship (WEC) with the ACO, which runs the 24 Hours of Le Mans. Although the three bodies share information and processes, even between these partners there are differences in the specification of the cars, which means the performance balancing cannot carry over directly.
Unlike the prototypes that run in the WEC and IMSA, the American body does not test the GT cars in its Windshear wind tunnel in North Carolina. Instead, it relies on data supplied by the FIA from its aerodynamic testing at the Sauber wind tunnel
