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Nitrogen in tires is becoming a popular replacement for standard air. Nitrogen is all around us... the air we breathe is 78% nitrogen, 21% oxygen and the rest is small amounts of other gasses. When it comes to tire inflation, nitrogen has many advantages over oxygen. With nitrogen tire inflation, improvements can be noted in a vehicle's handling, fuel efficiency and tire life through better tire pressure retention, improved fuel economy and cooler running tire temperatures. Here at the Get Nitrogen Institute our goal is to provide consumers, over-the-road truckers, fleet managers and others information about the benefits of using nitrogen in tires.

Fundamentally, air, oxygen and nitrogen will all behave exactly the same, in terms of just how much pressure will change for each 10 degrees of temperature change. However, temperature alone is not the whole story. Ambient air contains moisture, which nitrogen does not. If moisture is there, it contributes to a greater change in pressure, simply because at lower temp, water condenses to become a liquid. A liquid form of water occupies very little volume and contributes only a negligible pressure to the tire. But at higher temp, water becomes a gas; water evaporates inside the tire as temperature rises. With ambient air, which contains about 20.9% oxygen, the oxygen permeates through the rubber of the tire, so some leaks out. With nitrogen, containing only a little residual oxygen, pressure changes due to oxygen loss are greatly reduced. So, on both counts, the race car guys are correct; nitrogen is more predictable - nitrogen is dry; it has no moisture to contribute extra pressure changes with temperature. And nitrogen permeates out much slower than oxygen, so pressure changes due to that leakage are almost eliminated, compared with ambient air.

Let’s get a little deeper into the science. Keep in mind if the air in your tire today changes about 1psi for every 10 degree temperature change, a significant change in temperature will create a significant change in your tire pressure. Here is a set of Ideal Gas Law calculations, on the effects of a 10F degree temperature change, on either truck or passenger tires, filled initially at either 60F or at 90F. So, overall, about .8 psi per 10 degrees is one study and 2.2psi for truck tires, but the detail depends on the initial tire pressure and initial temperature.

Calculate pressure change expected for each 10F degrees temperature change:

The final pressure is calculated based on the Ideal Gas Law, where for this discussion on P and T change, while n, R, and V are fixed or constant.

P*V = n*R*T This is the Ideal Gas Law equation.

P/T = (n*R/V) by algebra, rearranging the formula for the Ideal Gas Law.

then

Pinitial/Tinitial = (n*R/V) = Pfinal/Tfinal since n, R, and V are all constant, that is,

it assumes no volume (V) change (i.e., no significant stretching of the tire rubber);

the "n" is how much gas is in a tire (the amount of gas is constant for this discussion, covering a time frame very short compared to the time it takes for gas to permeate through the tire rubber)

the "R" is the "ideal gas law constant" of proportionality, so it does not change either;

then

Pfinal = [Pinitial * (Tfinal/Tinitial)] by rearranging, we can calculate Pfinal by multiplying Pinitial by the ratio of Tfinal to Tinitial

Note: temperatures must be converted to Kelvin units (K), from Fahrenheit units (F), for this calculation.

Any questions about kits, parts, installations or services are welcome. Contact Bishop by phone at  866-867-8324 or e-mail bishop@bishopsales.com and we will respond promptly. If you're in the neighborhood, then drop by the shop at 1130 West 15th Street North Vancouver BC and we will gladly give you a tour of our facilities, but beware – there may be a Monster and ferocious horsepower beasts in our shop when you visit! We really love to share the fun with other performance enthusiasts who want to take their cars to the next level of performance, appearance and handling!

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