Fill 'em with pure nitrogen, please

But all along that compressed air was less than ideal for tires. In many cases, gas station air was poorly filtered, meaning lots of moisture, oil and other crud was getting inside tires. And while the air we breathe works fairly well for the human body, it is less than ideal for car tires.

Tire retailers are beginning to offer pure nitrogen gas as an alternative to compressed air, which has been the standard as along as pneumatic tires have been on the market.

As absurdly expensive tires and wheels have become more common on vehicles, it makes greater sense to take care of them -- and nitrogen does offer a number of big benefits, mainly in reducing leakage that lowers tire pressure.

Using pure nitrogen with all of the water and oxygen removed will reduce oxidation of the tire rubber and metal surfaces on the wheel.

Nitrogen is also supposed to move through tire rubber three times more slowly. Without any impurities, nitrogen also is subject to less expansion and contraction as the tire heats up and cools down during usage.

Regularly checking the air pressure in your tires is one of the most important parts of maintaining the safety of any vehicle, though many people never bother to do it. Keeping tire pressure at its proper level also dramatically improves fuel economy.

The air we breathe is about 79% nitrogen, with oxygen, carbon dioxide and other gases making up the balance. But the small amount of oxygen makes a big difference, obviously. Oxygen is highly active, causing corrosion and aging in many different types of material. By contrast, nitrogen is an inert gas, making it ideal as a filling medium where you want to retard corrosion.

It may seem like a gimmick, but nitrogen has long been used as a filling medium in the racing circuit, the military and the airline industry. But they have traditionally used bottled compressed nitrogen, which is far too exotic and expensive for tire retailers.

Nitrogen began making its first appearance on the U.S. retail market in a small way in recent years, but it took off last year as major compressor manufacturers introduced low cost systems for retailers.

Ingersoll-Rand, the nation's largest manufacturer of large compressors, introduced a system for retailers about a year ago. Other systems are on the market from smaller manufacturers, as well.