Also from what I understand its for consistency in car handling, because there is no moisture inside the tire the pressure will not change, that way they dont have to guess what there final pressure will be. When I run my Porsche on the track with street tires it is not uncommon to have the pressure's end up 6 plus pounds from where they started, and there is no way that I am pushing my tires anywere near the temperatures that the Nascar boys are! Rich 69 AMX (project) 70 Javelin (old man car) 77 Porsche 911 Euro (everyday go kart) .................................lost in New Jersey