This "solid paper" you’re likely after isn't just one document but a collection of industrial and academic research used to build the sim's realistic tire and bike behavior:
: TDR uses the Pacejka "Magic Formula" as the foundation for its tire physical model, which is the industry standard for simulating tire-road interaction forces. trackdayr.rar
If you are looking for an academic foundation for (TDR), the developers have explicitly stated that the game's physics are based on the work of Vittorio Cossalter , specifically his seminal book Motorcycle Dynamics . This "solid paper" you’re likely after isn't just