NASCAR Racing: NASCAR rules, nascar rules, tire wars

Question
I used to watch NASCAR several years ago.  At that time all teams were using nitrogen in their tires.  Now all I hear is "starting air pressure low and waiting for pressure to build-up".  Did I miss something? Is this illegal now?

Thanks,

Answer
Hi Wayne

Back then that was legal to use the nitrogen during the tire wars was going between,goodyear and hoosier and firestone but nascar did away with that due to safety standards.

Starting your air pressure is legal it gives your tires more grip on the turns but will wear out more then normal some teams are better on low air pressure then others.