I myself think the same thing Toronado thinks. But if that's not the case (in terms of HP) I think it might be based on how much the car handles. What I mean by this is that C class cars would probably be mostly FF vehicles along with a few FR's. B class would probably be stronger FF & FR cars. A class is probably all around with FR, FF, 4WD, and MR cars. And I guess the R class belongs only to the cars that can reach HP's of 900+ when fully tuned. But this is just mere speculation.