It to have racing tires and parts and not to show up in races with street cars (IB Allstars) as it is a race car and not street legal.
Show me where the Zonda has a 4 times bigger wing at the front.
Maybe the (real) Zonda R has more downforce then a FXX, but i doubt its 4times as much.
My opinion is PD made a mistake and made the FXX a street car instead of a race car.
(And for that reason only it has not so good brakes, downforce and hi-speed handling)
