Monday, June 4, 2012

The Facts About Nitrogen Inflation

In the last couple of years, inflating tires with nitrogen has gotten a lot of press.  Much of the hoopla is based on misinformation, so here’s the real story.

Nitrogen has been used in aircraft tires for a long time, for one main reason – it doesn’t support combustion, as air at the altitudes we live at does (because of the oxygen content).  Airplanes often operate at altitudes at which the air is much less dense than it is at ground level – that’s why they have those little oxygen masks that fall out of the overhead panel.  If something bad happens that creates a lot of heat in the area of an airplane tire, the heat could cause the tire to fail, releasing whatever gas is in it.  If that gas supports combustion, a fire could result.  A secondary benefit of nitrogen in airplane tires is that the bottled or generated gas they use is very dry compared to atmospheric air.  Moisture in a plane’s tire could condense, puddle, and freeze, leading to an out-of-balance tire when it lands.  This really is just a secondary consideration, because compressed air can easily be dried with equipment that already exists.  If you’re worried about the air in your tires supporting combustion, when your car is already driving around in air (your car is probably powered by an internal combustion engine, using atmospheric air), nitrogen inflation is for you.

One of the benefits claimed for nitrogen inflation is that nitrogen molecules are larger than oxygen molecules, so the theory is that it’ll leak out of your tires more slowly.  Well, air is almost 80% nitrogen.  Combine that with the fact that without special equipment that no shop has, it’s impossible to completely purge the air out of a tire when nitrogen-inflating it, and this theoretical advantage disappears – into thin air.  I read about a test in which 50 tires were inflated with air, and 50 were inflated with nitrogen.  A year later, the researchers checked the inflation pressures of all 100 tires, and found no statistical difference between the two groups.

Some people claim that their car rides better with nitrogen in the tires instead of air; I guess that 20% oxygen is pretty stiff.  I’m not going to dignify that absurd claim with further response.

Another “benefit” of nitrogen is less chance of corrosion of the wheel, tire and TPMS sensor.  Well, isn’t the outside of the wheel and tire rolling around in air??  Sounds dangerous!  Other claims, such as better fuel mileage, are equally silly.  Bottom line – if you want to partially fill your tires with slightly less oxygen and slightly more nitrogen, knock yourself out.  It does no harm.  Just so you know the facts.

Thanks for your time!

DOC Auto


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