Fill Your Tires With Nitrogen

From Ralph Kinney Bennett:

For years, over the road truckers, auto racers and the U.S. military have been filling tires on their vehicles with pure nitrogen. Here's why. In a tire filled with compressed air, the oxygen molecules tend to "migrate" through the wall of the tire over time. That's why, when you open the garage to check on your aunt's dust-covered 1980 Pontiac the tires are often flat. But nitrogen molecules migrate 3 to 4 times more slowly than oxygen, so tires stay properly inflated longer. There are other benefits. Nitrogen retains less heat than oxygen and therefore allows tires to run cooler.

While nitrogen is dry and benign and will not combine chemically with other materials (the metal in tire rims, for instance), compressed air contains trace amounts of water and the oxygen tends to combine with other materials, causing rust and corrosion. If you were to see the inner face (the part enclosing and sealing the inside of the tire) of some fancy aluminum wheels you would be surprised at how corroded they become due to oxidation.

Tour de France bicyclists fill their tires with nitrogen. So do NASCAR, Indy and Formula One racing teams, over-the-road truckers, some fire departments and the U.S. military.

Comments

[John]

This addition of nitrogen definitely works, especially to hold down temperature/pressure increases for running the sedan in track days. We've been using it in all our vehicles for about 10 years, and I'm especially pleased with the track day tires, and in the little boat trailer tires. Temperatures stay more stable, and "air" is lost more slowly from all the tires.

[SP]

So where does one find a list of stores that fill tires with nitrogen? I live in MA.

[tommy o]

I had to go to a local private airport and fill my own... with there tank.....

[Melissa Hodges]

"But nitrogen molecules migrate 3 to 4 times more slowly than oxygen, so tires stay properly inflated longer. "

Hate to be the bearer of bad news, but this is absolutely incorrect. the rate at which molecules leave the tire (called effusion, not diffusion), causing the gradual decrease in tire pressure is related to the weight of the molecule. It has absolutely nothing to do with the size of the molecule. Therefore, at the very least the excuse given by Costco is completely false.

Here's the reason...Molecules of lower molecular weight (i.e. nitrogen, compared to oxygen) move faster at any given temperature. At any temperature molecules of all gases possess the same kinetic energy. Kinetic energy depends on two things, velocity and mass. K.E. = mass x velocity squared. Hence, if the mass is lower the velocity has to be higher in order for the kinetic energy to be the same. Faster-moving molecules will escape from the tire faster. Nitrogen molecules have a mass of 28.02 atomic mass units. Oxygen molecules have a mass of 32.00 atomic mass units.

From a scientific standpoint, I cannot think of a single good reason for the average car ownder to pay for nitrogen to fill their tires.

[Tom Fuller]

Melissa,

What you're saying doesn't sound right to me. We use membrane systems to separate nitrogen from air for industrial puroposes - the membranes work just the same way as a tyre in this example. The link has more info.

http://www.onsitegas.com/what_is_membrane.asp

Cheers,

Tom.

[Jeff anderson]

Boat

[John Papinsick]

The nitrogen is retained in tires because of Fick's Law of diffusion and the solubility coefficient of the selected gases in the membrane of question (in this case, the rubber in the tire itself). For example SF6 has very little solibulity in rubber, so it will be totally retained in the tire. However, it is a Global Warming gas and not suited for this application.

[al]

this sounds like the put magnets on your gas line scheme to save gas back in the 70's

[Rob Wudrick]

Not to mention the fact that air is made up of about 78% Nitrogen anyway so supposedly this means that a tire should only lose about 22% of it's volume. It seems like a pretty good scam to get about $4 a tire out of uninformed consumers.

[Bob]

If o2 does leak out then why not just overinflate your tires by 20% then the o2 will leaks out and you'll have 100% N2 for free.