Tire Aging

• The National Highway Traffic Safety Administration has documented a decrease in tire aging when filled with nitrogen. Oxygen interacts with the rubber in tires, making it fatigue faster than with nitrogen, which is more inert.
  
  

Leakage

• Nitrogen is a physically larger molecule than many of the molecules found in air. This keeps nitrogen from escaping through the tires walls 30-40 percent slower than air, according to Consumer Reports.
  
  

Leakage Effects

• Tires underinflated by 12 psi (pounds per square inch) get 3 percent poorer gas mileage. The common cause of underinflation is gradual leakage and poor monitoring.
  
  

Pressure Variability

• The moisture in air varies in volume more over a range of temperatures than does pure nitrogen. Thus, areas that experience extremely high or low temperatures might see a lesser dip in tire pressure with nitrogen.
  
  

Cost

• Many tire stores have begun adding nitrogen to tires free of charge upon purchase, but when the customer is paying for nitrogen, it is arguable whether the benefits are worth it. Many of the benefits of nitrogen would be needed if car owners were more diligent about checking the air pressure of their tires.