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Originally Posted by thomschoon
Geez, the reason I thought they filled with Nitrogen was that it was "dry" and therefore provided a more even pressure in relation to the temp. Essentially your tire pressure stays stable as the tires warm up as there is no water to vaporize and expand, thereby provide more predictable handling. As for mixing with air, dont we breath around 80% nitrogen anyways and I havent burst in to flames lately  |
Hi,
Nitrogen (NČ in molecular form) is essentially (but not truly) inert and not easily reactive. It is non-flammable and referred to as a Dry Gas because it doesn't absorb moisture easily (though it does absorb some) as you point out. This means it expands less than a standard Air mixture, and is more consistent not varying with changes in Ambient Humidity.
But, another advantage is that Nitrogen molecules are essentially larger and therefore will diffuse more slowly from a porous material (such as a Tire) than Air would.
Normal Air is mainly Nitrogen and Oxygen (other gasses as well, but in insignificant amounts for this discussion). About 78% Nitrogen and 21% Oxygen. Since the Oxygen Molecule (OČ) is essentially smaller in diameter, it can leak easier and since it makes up basically 1 in 5 of the molecules in a given volume of Air, the tire can lose pressure more easily than if it were filled with Nitrogen alone...
Happy Motoring!... Jim'99