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Put nitrogen in your tires to save money?

Tara Baukus MelloIf you've visited a tire shop or taken in your car for service at the dealer lately, you've probably been asked if you wanted your tires filled with nitrogen and wondered if it was just a way for the shop to get a few extra bucks. At first glance, it seems like the small cost -- usually about $5 per tire -- is worth it for the benefits of nitrogen, but as it is with many things, there is more to it than meets the eye.

There are two issues with inflating tires with compressed air. The first is that all compressed air contains some water, which can be a very minor vapor or as substantial as actual water droplets. Water vapor or water droplets cause a larger change in tire pressure as the temperature of the tire changes. That causes additional wear and tear on the tire. Tire temperature changes not only from air temperature, but also from friction when the car is driven.

The second issue is that air penetrates through the tire's rubber more quickly than nitrogen, so the tire deflates more quickly, resulting in underinflated tires. This reduces fuel economy and handling and results in more wear. It can also lead to blowouts.

How you inflate your tires can impact your wallet, causing you to spend more money on gas and making you replace your tires sooner than you would like.

Tire shops and car dealers with nitrogen machines use these facts to help sell the nitrogen replacement. What they neglect to mention is that all tires are going to leak, whether they are filled with compressed air or nitrogen. Tests by the National Highway Traffic Safety Administration and Consumer Reports found that nitrogen-filled tires lost about one-third less pressure than the same tires filled with compressed air over the same time period.

While nitrogen escapes from tires more slowly and results in less dramatic tire pressure changes during driving, its benefits of improved fuel economy and slower wear only apply if the tires are properly inflated. And those benefits are identical with compressed air if the tires are properly inflated.

Just the same, filling your car tires with nitrogen may make good financial sense for some car owners. According to numerous studies, most Americans are driving cars with underinflated tires, which means they already are experiencing reduced fuel economy, greater tire wear and increased risk of a blowout. For these people, replacing the compressed air with nitrogen means their tires will stay properly inflated for longer, in theory saving them money.

Car owners still will need to check their tire pressure and refill their tires regularly in order to get the benefits. And they'll need to continue to refill with nitrogen. From this perspective, it's just as easy to create a reminder to check your tire pressure once a month and refill with a quality compressed-air source -- one without visible moisture when you depress the inflation nozzle with your finger -- for free or for a few quarters.

For those who decide to fill their tires with nitrogen, look for a service that provides free fill-ups, and make a note to visit that shop regularly to have your tire pressure tested to get the maximum benefits.

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If you have a car question, email it to us at Driving for Dollars. Read more Driving for Dollars columns and Bankrate auto stories. Follow her on Facebook here or on Twitter @SheDrives.

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