EarthTalk: Is nitrogen better than air for filling car tires?

Nitrogen doesn’t leak out as quickly, and well-inflated tires save gas. But cost is also a factor.

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    Pure nitrogen leaks out of tires more slowly than plain air does, and properly inflated tires improve mileage. But most drivers don’t check tires weekly, as they should.
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Q: Is using nitrogen to inflate my car’s tires really better for the environment than using air? And if so, how?
Roger Mawdsley, Abbotsville, BC

A: Whether or not it makes environmental sense to inflate car tires with nitrogen instead of air is a matter of much debate. Proponents of nitrogen say it is a smart choice primarily because it leaks from tires at a slower rate than air, so tires stay fully inflated longer. That, in turn, helps a vehicle attain better gas mileage. According to the Get Nitrogen Institute, a Denver-based nonprofit that advocates replacing the air in our tires with nitrogen, underinflated tires are a big contributor to global warming, as they cause drivers to waste fuel.

Although auto experts recommend checking your car’s tire pressure weekly, studies show that most drivers rarely if ever check to see if their tires are properly inflated and usually only add air when a tire is visibly low or beginning to go flat. A recent study by the European division of tiremaker Bridgestone found that 93.5 percent of cars in Europe have underinflated tires, wasting an estimated 2.14 billion gallons of costly, polluting fuel every year. Analysts believe that a similar percentage of North Americans are driving around on underinflated tires as well.

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While properly inflated tires certainly promote better fuel efficiency and so are  better for the environment, not everyone is persuaded that filling tires with nitrogen instead of plain ol’ air makes a difference.

Terry Jackson, who writes the influential “Driving for Dollars” column for the Bankrate.com website, points out that air is composed primarily of, you guessed it, nitrogen; some 78 percent of the air you put in your tires is nitrogen, with oxygen making up most of the remainder.

“So going to pure nitrogen only squeezes out a small amount of the oxygen molecules that nitrogen proponents argue are so detrimental,” ways Mr. Jackson.

Nitrogen proponents may quibble that it’s the oxygen in the mix that causes problems, though, as oxidization can start to degrade the rubber inside tires and corrode the interior of the wheels as well.

But Jackson counters that tires and wheels will have worn out on the outside  long before any oxygen-induced interior damage has an effect.

Also, he adds, a lot of the leakage from tires happens because a wheel and tire do not seal perfectly, and air (or nitrogen) escapes accordingly.

Another factor is cost. Specially equipped service centers will fill up your tires with nitrogen for something like $10 per tire, a far cry from the couple of quarters (if that) it takes to trigger the air machine at your local gas station. “When it comes down to a dollar decision, it’s hard to argue that spending as much as $40 for nitrogen on a set of tires is a good fiscal move,” writes Jackson. “Save your money and just keep an eye on your tire pressure,” he concludes.

Got an environmental question? Write: EarthTalk, c/o E – The Environmental Magazine, Box 5098, Westport, CT 06881. Or e-mail: earthtalk@emagazine.com.

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