Fill 'er Up -- With Nitrogen

You probably don't spend a whole lot of time thinking about your SUV's tires. Maybe you should, though -- the only place your SUV touches the ground is at your tires' contact patch. I would argue that your tires are the most important safety feature on your SUV. Keeping your tires properly inflated will make them last longer and perform better. Proper inflation will even help you get better gas mileage. But what should you fill your SUV tires with? How about Nitrogen?

At sea-level, the air we breathe is composed of approximately 78% Nitrogen, 21% Oxygen and 1% other gases. Ingersoll Rand Industrial Technologies sells a Nitrogen Generator system to fill tires with pure Nitrogen. Retailing between $5,300 and $12,500 (depending on capacity), the system is designed for commercial and professional applications, like tire shops and race teams. It works by filtering ambient air through a semi-permeable membrane to separate Nitrogen from ambient air. There are no tanks of liquid Nitrogen required.

Ingersoll Rand claims that there are several distinct advantages to filling your tires with Nitrogen:

• Better air pressure retention -- Nitrogen doesn't seep out through the tire walls like Oxygen can, so tires remain fully inflated longer.
• Enhanced fuel economy -- Nitrogen dissipates heat faster than air, and heat causes rolling resistance. "Maintaining tire pressure can boost fuel economy by as much as 6 percent."
• Longer tread life -- Filling your tires with pure Nitrogen makes tires run cooler, which will reduce tire failure. It also prevents oxidation, which can cause tread separation and belt failure. Since Nitrogen doesn't carry moisture, it won't cause rust on the inside of rims and valve stems.
• Slow chemical aging -- "Filling a tire with Nitrogen also significantly slows the chemical aging process of the tire's rubber components."

It costs between $3 and $10 per tire to get your SUV running on a cushion of Nitrogen. Is it worth it?

There's significant debate about the value of filling your tires with Nitrogen. On Eng-Tips Forums, a web board for engineering professionals, the "Nitrogen filled tires?" thread is full of passionate discussion, most of it quite skeptical about the practical benefits of the practice. The consensus opinion on Eng-Tips Forums seems to be that the benefits of Nitrogen are largely academic -- tires are engineered to be filled with ambient air, wheels are designed to cope with the moisture that air carries, and the benefits of Nitrogen, in real world applications, though real, are not worth the cost.

My bottom line advice: Save your money, and keep your tires properly inflated with air. You'll get much better results investing in a small compressor for your garage and keeping your SUV tires properly inflated with air. If your local tire shop has a Nitrogen Tire Inflation System, see if you can get them to include a free fill-up with Nitrogen when you buy your next new set of tires, and try it on for size. Do some real-world tests and join the debate.