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Nitrogen for TiresNotes From The Road

Nitrogen for Tires
By Wayne Scraba/

Choosing Between
Compressed Air or Nitrogen for Your Tires

Today, you’ll notice green Nitrogen “filling stations” at tire shops across the continent. Typically, filling a tire with Nitrogen costs in the range of $10 per tire (although a few shops include it for free when they sell you a new set of tires). Using compressed Nitrogen instead of compressed air isn’t really new. The military, commercial airplanes, race cars and even the space shuttle have used it for years.

So far so good, but what’s the difference between simple air and nitrogen? The atmosphere of the earth is composed primarily of Nitrogen (78%), the remaining balance is a mixture of Oxygen (21%) along with a small percentage of Ozone, Argon and Carbon gases. When you remove Oxygen, it also means you remove water because water is two parts Hydrogen gas and one part Oxygen gas. In turn, that means the use of pure Nitrogen in tires prevents corrosion (more below), but there are other advantages.
Nitrogen Benefits 
What’s the big benefit? [omitted; see footnote Page 2*] Michelin Tire Manual points out that a tire inflated with Nitrogen loses its pressure three times slower compared to one inflated with compressed air. Ingersoll Rand goes further: “diffusion out of the tire sidewall is 30 to 40 percent slower than Oxygen. That’s why a Nitrogen-filled tire maintains pressure longer.” For cars with (expensive) custom wheels, an even bigger benefit could be the fact Nitrogen prevents oxidation (due to the lack of water). Oxidation leads to tread separation, but it also leads to corrosion of the rim. Don’t believe it? Forget to drain an air compressor after a few days of use and you’ll see just how much water is found in good fashioned compressed air.
Proponents of Nitrogen-filled tires point out that Nitrogen maintains pressure much better than compressed air. Proponents of compressed air point out it isn’t difficult to check and refill tires, even on a weekly basis.
Nitrogen proves largely inert, from a chemical perspective at the relatively low operating temperatures experienced by automotive tires. That means Nitrogen will not attack the rubber in tires like Oxygen does. Keep in mind that many tires use steel belts. The steel, obviously, is not immune to attack by moisture in found in compressed air. Apparently, both Ford Motor Company and the NHTSA have studied this phenomenon, and have concluded it can be a problem for tires used over a long period of time or under harsh conditions.
Another benefit proponents of Nitrogen note is the fact Nitrogen is slightly lighter than air. In theory, this will reduce unsprung weight and the car will exhibit better performance. There is a catch however: The weight difference we're discussing works out to less than 4% of the gas in the tire. That calculates to a reduction of less than an ounce for most vehicles. Whether this is beneficial or not might be a moot point, particularly in a street-driven automobile.

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