Jan 4, 2023
Is there really an advantage to using nitrogen in tires rather than air? Well, sort of...
Race cars and airplanes run nitrogen in their tires so it makes sense to run them in passenger vehicles and light trucks, right? Yes and no…
Understanding the fundimentals of nitrogren should be a determining factor when deciding what is right for you and if the costs outweigh the benefits.
Nitrogen and Air
Traditionally, car tires have been filled with compressed air. Air is 78 percent nitrogen and just under 21 percent oxygen, and the rest is water vapor, CO2, and small concentrations of noble gases such as neon and argon. In its pure form, nitrogen has been used primarily because it doesn’t support moisture or combustion. Nitrogen is an inert (non-flammable) gas – basically, nothing more than dry air with oxygen removed.
Because of nitrogen’s inert properties, it is often used in highly specialized tire service applications and/or demanding environments. These tire service applications usually include aircraft, mining, and commercial/heavy use. Also, nitrogen is used in professional auto racing where extreme vehicle speeds are involved. Dry nitrogen is used in this regard to help reduce tire pressure variations where even small differences in pressure can affect vehicle handling at the extreme limits of performance.
For normal everyday consumer tire service applications, nitrogen tire inflation is not required when “dry” compressed air is used.
It All Comes Down To Moisture
Nitrogen-filled tires retain their pressure longer? A normal tire filled with regular air loses an average 1 to 2 PSI (pounds per square inch) per month. It’s true that there is a slower loss from nitrogen-filled tires. But this improvement is slight — only about 1.3 PSI less over the course of an entire year, according to Consumer Reports. Nitrogen will slow the amount of tire inflation loss to about one-third of what you’ll experience with air. This means instead of losing one to two PSI per month, you’ll lose ⅓ to ⅔ PSI per month. You’ll still need to check and top off your air roughly every other month to stay within the ideal inflation range.
Nitrogen gas does not expand as much as compressed air? Regular air has a lot of moisture in it. This moisture is a major reason the tire pressure fluctuates. Nitrogen is DRY so it will not expand as much when heated. Most reputable tire shops will use air dryers to provide dry compressed air. The difference in expansion between nitrogen and dry compressed air is nominal. Testing pressure increases using nitrogen and dry air indicate no PSI difference between the two gases. Temperature range test between -29°C and 57°C noted a change of PSI from 80 to 108 for both Nitrogen and Dry Compressed Air. Keep in mind that the “air” used in this test is clean and dry.
Using moist air, (using compressor in driveway on a humid day), will contain more wator vapor and that’s where the difference in PSI will factor in. Moist air 25 PSI and 27°C heated to 72°C will increase to 35PSI while nitrogen will increase to only 30PSI – a difference of 5 PSI. With this in mind, it makes sense that nitrogen would be a better option as it is dry, but then again, so would dry compressed air.
Reason for Nitrogen In Extreme Use
For the average passenger car, truck or RV, tire temperature extremes are usually less than 66°C Where things get serious is when the temperature goes above 100°C (boiling point). Above this temperature the additional vapor pressure rises significantly. In other words, the pressure increases exponentially rather than linearly or straight line and climbs ever more rapidly as the temperature rises further. This can easily add 20-30% more pressure increase than if there were no moisture inside the tire and gets much worse as the temperature rises higher.
NASCAR, for example can see tire temperatures reach 94°C so using a clean dry gas for tire inflation is important. Any moisture under these extremes would create dangerous pressure increases and because nitrogen has a much more consistent rate of expansion and contraction.
AIRLINER tires are subjected to the daily punishment of multiple takeoffs and landings. Tires are exposed to temperatures below -40°C during cruise. At touchdown, rubber temperatures can momentarily exceed 200°C. Nitrogen-filled tires reduce the chance of fire or explosion (it’s an FAA regulation). Tire rubber is flammable and wheel brakes reach very high temperatures. A large tire with 200 psi of atmospheric air would provide a lot of oxidizing power to feed a fire. Nitrogen does not support combustion, greatly reducing the risk of a tire fire or explosion. (Photo: MD-11 landing gear tire pressures and brake temperatures.)