Special Pre-tuned Power Packs that span a variety of cars allowing vehicles to compete together closely and fairly.
Ex: An "All-Star DTM" pack would allow the Mercedes 190 Touring Car (four cylinder, rear wheel drive), Opel Calibra touring car (Turbo Six Cylinder, All wheel drive) and the Audi A4 touring car (V8, rear wheel drive) to compete on fair terms by everyone simply purchasing the pack. Online rooms can then select a pack (or packs, if a multi-class feature is desired) to restrict the cars by, ensuring varied but clean and fair racing.
However, each car would have multiple choices. We'll use the DTM cars again to make the point. An Opel Calibra could have at least three different Packs to pick from. 1: '90's DTM pack to performance balance it with the Alfa Romeo. 2. All-Star DTM, as stated above. 3. "GT All-stars R Class" Which would be a blanket modifier that would balance DTM, LMS GT, FIA GT, Fictional GT and other cars together to race competitively.
Each car, be it road or racing type, would have at least 2-3 options to balance it with a wide varietty of other cars, so that racing can be close and competitive, without needing one-make fields of cars.