Originally Posted by Blogson
Since the earth's atmosphere is about 80% nitrogen anyway it doesn't seem logical that there would be an enormous and cost effective benefit from inflating tires with 100% nitrogen. ???
Bingo! The main advantage of nitrogen is that the process of separating and compressing it makes it really dry, almost no moisture at all. The only other minor advantage is that the permeability of nitrogen through rubber is slightly less than for oxygen. This means the tires should not loose pressure as quickly, the difference is very small
There's a misconception our there that nitrogen doesn't expand as much as air with temperature increase. This is not true because all gasses follow the ideal gas law Ideal gas law - Wikipedia, the free encyclopedia
. This law is not sensitive to the chemical nature of the gas, so there would be no difference between air and nitrogen, besides as previously pointed out, air is already 79-80% nitrogen anyway. The other misconception that you tires will run cooler is also not true. Inflated properly there is no difference between air and nitrogen. Theoretically if one did not check their tire pressures for 6mo or more the air filled tires might loose marginally more pressure and therefore run a bit warmer due to the extra rolling resistance and tire flexure. This is a side effect rather than a direct property of using nitrogen though
What causes larger pressure changes with air filled tires is the presence of moisture. Water can change phase from liquid to gas and back, the gas or vapor phase of water occupies a lot more space than the liquid phase, hence when you convert more of it from liquid to gas with heat, you get a pressure increase greater than it ideal gas law predicts. perfectly dry air would perform exactly the same as dry nitrogen in this respect.
I guess for winter driving a good dry fill is not a bad idea. I've seen poorly maintained air compressors that spray a fog of moisture when the filler trigger is pulled. That much water in your tires might be enough to puddle, freeze and throw your tires out of balance!