TCS Daily


Fill 'Her Up... With Nitro

By Ralph Kinney Bennett - November 16, 2004 12:00 AM

I'm pretty attentive to my cars. I tend to keep them a long time and try to keep them running well. But even I have to admit I don't do a good job of checking my tire pressure.

Sure, I walk around and take a look at them when I'm at the gas station, and if they don't seem noticeably saggy, that's fine.

Well, that's not a good idea. Improperly low pressure makes tires overheat and wear out much more quickly. And as we've all been reminded scores of times, it also causes a definite deterioration in car handling and a noticeable drop in gas mileage.

If you could see an underinflated tire rolling in slow motion you'd see why. Tortuous warping takes place as the tire meets the pavement. This puts a huge strain on the tire body itself and dramatically increases the tire's "rolling resistance."

A properly inflated tire, on the other hand, has a much smaller contact area with the pavement. It's "rounder" and therefore rolls more smoothly and efficiently, putting much less strain on your engine, transmission, rear axle or transaxle.

Over time tires lose their proper inflation pressure naturally (air actually escapes imperceptibly through the tires themselves) and although you the driver may not notice it, your car is gradually working harder to maintain a given speed.

I bicycle every day, so I am dramatically aware of the "drag" caused by underinflated tires. If you have a bike, let just a little air out of your tires and ride it around the block. See how much harder you have to work to move along. You use more energy and you know it. But in your car you're somewhat isolated from your tires and the sound of your engine and unaware how much more energy (and therefore gasoline) you're using to go a given distance.

The gas mileage gains for properly inflated tires may be more significant that you would think. Some state and federal studies have shown that motorists often are driving with tires 8 to 18 pounds under proper inflation pressure. One study showed that in a car running with tires at 24 pounds per square inch (psi), increasing tire pressure to 32 psi increased gas mileage by 3 miles a gallon. At today's prices that's pretty good.

Although, as I have mentioned, I'm a little recalcitrant, I do try to keep my tires inflated to the maximum pressure listed on the tire (you'll see it in raised numbers somewhere on the sidewall of your tires).

Expert drivers in fuel economy runs have always known this and they superinflate their tires, running at 100 pounds per square inch or more. Don't do this! It's mucho dangerous. These guys are usually using special tires under special conditions. Just follow the "max pressure" readings on your tires and, more important, keep checking them.

And here's something that can help you. An old technological fix, known to the experts but not very well known to the public, can keep your tires running for long periods at ideal pressure.

It's nitrogen. Yep. Good old nitrogen -- that unglamorous inert gas that constitutes about 78 percent of the air we breathe.

For years, over the road truckers, auto racers and the U.S. military have been filling tires on their vehicles with pure nitrogen. Here's why.

In a tire filled with compressed air, the oxygen molecules tend to "migrate" through the wall of the tire over time. That's why, when you open the garage to check on your aunt's dust-covered 1980 Pontiac the tires are often flat.

But nitrogen molecules migrate 3 to 4 times more slowly than oxygen, so tires stay properly inflated longer. There are other benefits. Nitrogen retains less heat than oxygen and therefore allows tires to run cooler.

While nitrogen is dry and benign and will not combine chemically with other materials (the metal in tire rims, for instance), compressed air contains trace amounts of water and the oxygen tends to combine with other materials, causing rust and corrosion. If you were to see the inner face (the part enclosing and sealing the inside of the tire) of some fancy aluminum wheels you would be surprised at how corroded they become due to oxidation.

Tour de France bicyclists fill their tires with nitrogen. So do NASCAR, Indy and Formula One racing teams, over-the-road truckers, some fire departments and the U.S. military.

And now, in a typical example of the confluence of technology and markets, high gasoline prices and continuing concerns about tire safety are bringing about a growing interest in nitrogen.

Big discounter Costco has begun offering nitrogen fill-ups on new tires in some of its tire centers. Pep Boys has been test marketing nitro at some of its tire shops in the south. Several small tire chains in Florida, New York and Ohio are doing the same.

Branick Industries, of Fargo, N.D., one of the nation's leading suppliers of equipment for tire, wheel and suspension services, builds a nitrogen inflation system that takes air from a garage or service center's air compressor and passes it through an internal membrane that separates out the abundant nitrogen molecules.

The pure nitrogen is compressed and stored in this "nitrogen generator" and or a back-up tank next to it, from which tires are filled. Costco is filling new tires with nitrogen for free. Some dealers charge $2 per tire and up to $5 apiece on tires not sold by them.

It's a safe bet you'll be hearing more about nitro and seeing an increased availability of nitrogen fill-ups as you shop for tires or maintain your present ones. In the greater scheme of things this is no big deal. But like the improvements that have been made in the inner workings of automatic transmissions over the past 50 years it is one of those gains in efficiency that we often take for granted. It is one of those little refinements and improvements that are routine in a vigorous, free and therefore infinitely articulate market.


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