Filling your car's tires with nitrogen not worth the added cost
The pricey gas doesn't sharply reduce leakage or rubber deterioration
Dear New Frugal You,
I just recently purchased a car utilizing Consumer Reports' car pricing plus various Internet sources. The car has tires filled with nitrogen, and it appears that a few dealers are going to that. (There are claims that nitrogen is better.) Is that true? Is nitrogen really better than air in your tires? -- Becky
Becky, you're right. Many dealers and tire centers are encouraging consumers to fill their tires with nitrogen instead of air. Typically they charge about $5 per tire for a nitrogen fill. They insist nitrogen-filled tires get better gas mileage, decrease tire wear and increase safety.
The science behind the proponents' assertions that nitrogen is better in car's tires boils down to two claims: that nitrogen slows leakage, and that it retards your tires' deterioration.
All tires leak some air. A tire that's underinflated will reduce gas mileage, increase tire wear and, in extreme cases, could damage the tire and cause it to become unsafe. Nitrogen escapes from tires at a slower rate than air. So a nitrogen-filled tire stays closer to its proper level of inflation.
The second factor is based on the fact that rubber deteriorates over time. Part of the deterioration is due to the rubber's exposure to oxygen (a component of air). Replacing oxygen with nitrogen slows this deterioration.
An interesting factoid for office cooler conversation: Air is already 78 percent nitrogen; only 21 percent is oxygen.
According to the National Highway Traffic Safety Administration (NHTSA), "More than a quarter of automobiles and about a third of light trucks (including sport utility vehicles, vans and pickup trucks) on the roadways of the United States have one or more tires underinflated 8 pounds per square inch (psi) or more below the level recommended by the vehicle manufacturer."
So the potential savings could be great if nitrogen performs as claimed. Fortunately for us, Consumer Reports did a yearlong test in 2006-2007. They took identical tires and filled them to 30 psi. The air-filled tires lost an average of 3.5 psi. The nitrogen-filled tires did a little better, but still lost 2.2 psi.
An NHSTA test of hundreds of tires found the same thing, that nitrogen filled tires lost approximately two-thirds as much pressure as air filled ones.
They also found that tires filled with nitrogen had the same rolling resistance as tires filled with air. So any increase in mpg would come solely from proper inflation.
Given those facts, Becky, you'll still want to check your tires every month or so. You can't count on the nitrogen to eliminate low tire pressure. So any benefit is minimal. Plus, there's a disadvantage. If you want to maintain the nitrogen, any refills will need to be with nitrogen. Not air. That means refills will become less convenient and more costly.
What about the tire deterioration issue? NHTSA tested both air and nitrogen filled tires for aging. They found the results were "inconclusive."
So when you show off that new car to your friends, you can tell them how the you got a great deal on your car. And, you can also tell them that after conducting thorough research, you wouldn't pay extra for nitrogen filled tires.
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