i work at big o tires and it does help your mpg and i cost 20 bucks listen to this the gas stations witha green hose for air guess what nitro ya thats right because regualer air has moisture in it and it breaks the machine and nitro dont and most of the time people at my work dont even put nitro in the tires i do im not mean but ya just got to a gas station with a green hose put about two psi over bc there is a little bit of air in the nitro and when the weather changes the nitro will be left by itself

Dear Cecil:

I caught a segment on some car show about modding up your car. One of the things they mentioned was the benefit of filling your tires with nitrogen instead of air. Considering I fill my tires with air and don't have much of a problem constantly refilling them, what is the straight dope on nitrogen in car tires?

— Dave from Massachusetts

Oh, there are plenty of benefits: (1) Cool fluorescent green valve stem caps (assuming your nitrogen vendor has any marketing savvy), which will look sharp with your spinning wheel covers. (2) Bragging rights. OK, you were behind the curve with cell phones, iPods, thong underwear, etc. Nitrogen in tires is relatively new to the mass market. Now's your chance. (3) Reduced fire danger next time you land your space shuttle or commercial aircraft, and tell me you won't sleep better knowing that.

Most tires are filled with compressed air, which when dry consists of about 78 percent nitrogen, 21 percent oxygen, and 1 percent other gases by volume. Water vapor (humidity) can make up as much as 5 percent of the volume of air under worst-case conditions. Filling your tires with nitrogen mainly does two things: it eliminates moisture, and it replaces skinny oxygen molecules with fat nitrogen molecules, reducing the rate at which compressed gas diffuses through porous tire walls. That means, theoretically at least, that a tire filled with nitrogen retains optimal pressure longer, leading to more uniform tire wear and better gas mileage. The commonly quoted figure is that tires inflated to 32 psi get 3 percent better mileage than at 24 psi.

Does nitrogen make any practical difference? You couldn't prove it by me. I found no scientific tests showing that nitrogen-filled tires stayed inflated longer than average under normal conditions. A car-buff buddy was sure it worked but conceded he had only anecdotal evidence that it did.

As for moisture, changes in humidity affect tire performance two ways. First, the density of humid air fluctuates more with temperature than that of dry air, so removing humidity can keep your tire pressure more consistent, especially when the temperature climbs over 100 degrees Fahrenheit. That may be a legitimate concern in Formula One racing, but it's not much of an issue if you're just tooling around town.

Humidity can also be a factor in wheel maintenance - since pure nitrogen doesn't have moisture in it, supposedly your wheels won't rust as quickly, which could lead to improved wheel performance and air sealing. The question is, how big a problem is wheel rust these days? According to a few tire and wheel shops we contacted, not very. Seriously rusted wheels are uncommon in typical steel-wheeled cars, and many high-performance cars have alloy wheels that don't rust at all. One exception is work vehicles such as dump trucks, which are exposed to a much harsher environment.

Another claim I've seen is that since nitrogen is slightly lighter than air, you'll save weight and get better performance. However, we're talking about a weight difference of less than 4 percent of the gas in the tire - in other words, a difference of less than an ounce for most vehicles. A possibly more realistic benefit is that nitrogen is largely inert chemically at low (i.e., normal) temperatures, so it won't attack the rubber in your tires like oxygen does. Oxygen attack is something both the National Highway Traffic Safety Administration and Ford Research have studied, and can be a problem for tires used for a long time or in rough conditions.

More important, nitrogen doesn't support combustion, which is one reason aircraft and the space shuttle use nitrogen in their tires. The wisdom of this precaution was brought home by the crash of Mexicana Airlines flight 940 on March 31, 1986. Shortly after the Boeing 727 took off from Mexico City en route to Puerto Vallarta, an overheated landing-gear brake caused a tire improperly filled with air instead of nitrogen to overheat as well and explode, rupturing fuel and hydraulic lines. The ensuing fire and crash killed 167 passengers and crew. However, unless your driving habits are of the X-treme variety, the chances of your tires catching fire anytime soon are slim.

Overall, filling up with nitrogen won't hurt and may provide some minimal benefit. Is it worth it? If you go to some place like Costco that does it for free with new tires, sure, why not? Elsewhere, though, I've seen prices quoted as high as $10 per tire, which is way more than I'd pay. Rather than shell out for nitrogen, you'd be better off just checking and adjusting your tire pressure regularly, something the NHTSA says less than 60 percent of U.S. motorists actually do.

By TIM MORAN
Published: March 9, 2008

EARL STEWART spends about $50,000 a month honoring his lifetime tire-replacement guarantee for many of the cars he sells at his Toyota dealership in Lake Park, Fla. He hoped that using nitrogen to fill those tires would save him money by getting the tires to last longer. It didn’t.

In an eight-month trial, he equipped several vehicles with nitrogen-filled tires. When his staff measured tire pressures and compared the wear with air-filled tires, they found minimal differences.

“It sounds good, and it’s an easy sell, and people want to believe it,” said Mr. Stewart, who decided to stick with ordinary air. “Even my parts department wanted to believe it.”

Mr. Stewart was hoping that nitrogen would reduce the wear on the tires because the gas takes longer to leak from a tire then ordinary air. Tires low on air wear quicker and need to be replaced sooner than tires filled to the correct pressure.

Ashok Mathur, business manager for nitrogen tire inflation at Air Products and Chemicals in Allentown, Pa., said that owners could save up to $100 a year by keeping tires properly inflated, even with air, but that it’s easier with nitrogen, which takes 30 to 40 percent longer to leak out.

In its January issue, Consumer Reports magazine published data on a nitrogen experiment. Over a year, tires filled with nitrogen lost less pressure than those with air, losing 2.2 pounds a square inch, compared with 3.5 for air.

Nitrogen Filled Tires: a Scam?
Posted on July 5, 2008 by cfeagans

While this is primarily an anthropology and archaeology blog, I also like to write about skeptical topics as well. I’ve written several bits about pseduoarchaeology in the past, but this topic is a straight bit of skepticism.

My wife and I recently traded in one of our 2000 model Saturns for a new 4-cylinder Ford. Having sold new cars for a living about 8 years ago (that’s how we ended up with two Saturns!), my wife knows the car business and wasn’t about to let anyone sell her any add-ons, after market B.S., extended warranties, and all the other sorts of insurance the dealers really make a fair bit of money on. Indeed they were completely frustrated that she and I wouldn’t even bat an eye at what they had to offer.

But, when the finance manager went into his pitch on Nitrofill. This is essentially a service they provide to periodically fill the tires with nitrogen instead of normally compressed air. The difference, he stated, is that “nitrogen filled tires don’t loose pressure as fast as air and nitrogen doesn’t oxidize the inside of the tire as fast.”

I looked at my wife and saw a bit of hesitation. She was buying it. Literally, if I dindn’t stop her. “Ahem,” I got her attention and she snapped out of it. “Isn’t air already 78% nitrogen?” I asked the finance manager. “Uhh… well I’m not a scientist,” he replied with a sheepish grin. My wife, fully back to her senses smiled broadly, pointed at me and said, “but he is!” I’m not, but having stayed at my share of Holiday Inn Expresses, and having paid some attention in my Chemistry classes, I knew $5.00/tire every time they got low wasn’t an expense I wanted. And, if we filled a tire with air somewhere else, it would be $60 to service the tire and fill it back up with nitrogen. The tire that already had 78% nitrogen.

Needless to say, I we didn’t buy the nitrogen scam. And that’s just what it is. On the surface it sounds good. In fact, if it were free, I’d take pure nitrogen over normal air any day. But I’m not about to let a car dealer or service station sell me the air in my tires.

The claims are this:

1. Nitrogen-filled tires maintain proper pressure longer
2. The rubber of nitrogen-filled tires last longer
3. Nitrogen is less volatile than oxygen and thus safer in a fiery crash
4. Cars with Nitrogen-filled tires get better gas mileage
5. Cars with Nitrogen-filled tires are better for the environment

The last two claims are dependent upon the expectation that the tires filled with nitrogen are actually at properly inflated pressure more consistently. So let’s set them aside and focus on the first three points.

1. Do nitrogen-filled tires maintain proper pressure longer? The premise for this claim is that nitrogen is a larger molecule than oxygen. It is. Only slightly. But let’s not omit the fact that we’re talking about molecules here and not just the element. Oxygen and nitrogen are both diatomic molecules. Nitrogen actually has less mass than oxygen, so Graham’s Law dictates that it diffuses a bit faster than oxygen. However, since the actual size of the oxygen molecule (O2) is a bit larger than that of a nitrogen molecule (N2), this only applies if the opening from which the molecules are effusing from is large enough to permit the largest of the two. In such cases, N2 will diffuse faster.

The question, then, becomes, are the pores in rubber (assuming there are such pores) smaller than the N2 molecule but larger than the O2 molecule? I don’t know the answer to this. Nor could I find any literature in the few minutes I searched, but if anyone has a citation to an independent (i.e. non Nitrogen Tire industry) study or bit of research, I’m interested. Without digging out my old chemistry textbook, I’m willing to tentatively accept Wiki Answers on the sizes of N2 and O2 molecules: N2 is roughly 300 picometers while O2 is slightly smaller at 292 picometers. I’m open to revising these figures if someone cites a more reliable source, but I can’t imagine that there’d be any reason for the link to be more than slightly wrong.

2. Does rubber oxidize faster when exposed to oxygen rather than pure nitrogen? I’d expect so. The real questions are: a) how to you keep oxygen on the outside of your tires from causing oxidation?, and b) does it really matter to me since every single tire I’ve ever replaced was because of worn tread and not oxidation?

3. Why do I give a **** whether or not the oxygen in my tires will fuel the fire of my fiery crash? If the explosion is powerful enough to consume the oxygen in the surrounding air leaving only my tires as reserve fuel, I suspect I’m going to be a crispy critter anyway.

As for 4. and 5., I’m not that arsed for time that I can’t continue my routine of checking my tire pressure every 3,000 miles when I change my oil. In fact, nearly every time I’ve ever checked my tires at 3k, they’ve either been dead on for the proper psi or just a pound or two off. Whenever I’ve had to fill more than that, it’s been either because of a faulty valve or a nail in the tire itself. I suspect that the resulting points of egress in a faulty valve or pucture would create holes large enough for either O2 or N2 to escape through effusion. So, in that case, Graham’s Law would be in effect and N2 would escape faster than O2.

The bottom line: if nitrogen becomes a free option, easily obtainable (i.e. cheaper and easier than the $5.00 Walmart compressor that I plug into my cigarette lighter), I’ll use it since there’s a very slight chance I won’t need to top off my tire pressure as often. But, as long as I have to pay for it or even just drive to the dealer for it, I call bull****!

Nitrofill is a scam. Nitrogen-filled tires for general consumers is a scam.

Inflating car tires: Air or nitrogen?
By Terry Jackson • Bankrate.com




As if the tangled task of maintaining your vehicle without draining your bank account isn't tough enough, some of the folks who sell and service the tires on your car have come up with another item for your consideration:
- advertisement -

Would you like regular air or nitrogen with your tires?

Nitrogen?

OK, expect to be charged as much as $10 per tire for that choice.

Is it worth it? Let's check the basics.

You might trace this latest kink to the concerns of several years ago about blowouts on SUVs, particularly the Ford Explorer equipped with Firestone tires. What's at issue with nitrogen versus plain old air, which comes from the pump at the gas station, is that nitrogen is a dryer, more stable gas that's less prone to changes in pressure due to heat or cold.

Nitrogen has long been used in aircraft tires and in the tires of race cars. Its use in average road cars is new and controversial.

Proponents of nitrogen argue that since studies show that fewer than 60 percent of drivers rarely if ever check the inflation of their tires, anything that will slow the normal leakage -- estimated by some at 1 to 2 pounds per square inch a month -- is a good safety measure.

One Web site that lays out the claims for using nitrogen is www.getnitrogen.org.

It says, essentially, that putting nitrogen in your tires will increase your fuel efficiency because properly inflated tires will reduce rolling resistance, which can mean as much as a 3 percent better mileage than a car with under-inflated tires.

It also claims that nitrogen will not degrade the interior rubber of the tire or corrode the wheels, since it contains no oxygen or water vapor -- both present in the atmosphere we breathe and pump into our tires.

But a closer examination of the facts makes some of the claims for nitrogen seem at best anecdotal or illusory for everyday drivers.

First, the air around us is already 78 percent nitrogen, with 21 percent oxygen and 1 percent other gases. So going to pure nitrogen only squeezes out a small amount of the oxygen molecules that nitrogen proponents argue are so detrimental.

Also, the advantage of nitrogen being more stable and less prone to changes in pressure due to heat in the tires seems of little benefit to average drivers. Race teams use it because they can change the handling of the car by adjusting individual tire pressure by as little as a quarter pound. So having a gas that's ultra stable has real benefits when dealing with such small degrees.

Nitrogen proponents say that the nature of the gas means it's less prone to leaking out over time through the pores present in rubber tires. But most air leakage in tires can be traced to poor fit around the rim of the wheel or the valve stem, rather than gas permeating through the rubber.

Claims of nitrogen being more friendly to the rubber and wheels is also questionable, since most tires wear out the tread on the outside long before the inner rubber would go bad from exposure to oxygen. The same factors hold true for wheels, many of which are made from alloys, not straight steel. You're far more likely to damage a wheel from hitting a curb than see a wheel go bad from oxidation.

A good site that takes a contrarian point of view on nitrogen in passenger car tires is www.eng-tips.com, which is run by engineers.

When it comes down to a dollar decision, it's hard to argue that spending as much as $40 for nitrogen in a set of tires is a good fiscal move.

Even if you accept the arguments of proponents, at some point you are going to have to add air to your tires -- not even the most ardent nitrogen pushers will say that your tires will never lose pressure. When that happens, you're most likely to go to the corner gas station, put in a couple of quarters and pump your tire up with regular old air, which will mix with the nitrogen and degrade its benefits.

Save your money and just keep an eye on your tire pressures.

Dear EarthTalk: Is using nitrogen to inflate my car’s tires really better for the environment than using air? And if so, how?
-- Roger Mawdsley, Abbotsville, BC

Whether or not it makes environmental sense to inflate car tires with nitrogen instead of air is a matter of much debate. Proponents of nitrogen say the element is a smart choice for the environment primarily because it leaks from tires at a slower rate than air, so tires stay inflated longer at full capacity, which helps a vehicle attain maximum fuel efficiency, i.e. better gas mileage. According to the Get Nitrogen Institute, a Denver-based non-profit which advocates for replacing the air in our tires with nitrogen, under-inflated tires inadvertently are a big contributor to global warming as they cause drivers to waste fuel.

Although auto experts recommend checking your car’s tire pressure weekly, studies show that the majority of drivers rarely if ever check to see if their tires are properly inflated and usually only add air when a tire is visibly low or beginning to go flat. A recent study by the European division of tire maker Bridgestone found that 93.5 percent of cars in Europe have under-inflated tires, wasting some 2.14 billion gallons of high-priced, polluting fuel every year. Analysts believe that a similar percentage of North Americans are driving around on under-inflated tires as well.

While properly inflated tires certainly promote better fuel efficiency and are thus good for the environment, not everyone is convinced that filling tires with nitrogen instead of plain ol’ air makes a difference. Terry Jackson, who writes the influential “Driving for Dollars” column for the Bankrate.com website, points out that air is composed primarily of, you guessed it, nitrogen; some 78 percent of the regular air you put in your tires is nitrogen, with oxygen making up most of the remainder. “So going to pure nitrogen only squeezes out a small amount of the oxygen molecules that nitrogen proponents argue are so detrimental,” relates Jackson.

Nitrogen proponents may quibble that it’s the oxygen in the mix that causes problems, though, as oxidization can start to degrade the rubber inside tires while corroding the interior of the wheels as well. But Jackson counters that tires and wheels will have been long worn out on the outside before any oxygen-induced interior damage causes them to come apart. Also, he adds that a lot of the leakage from tires happens because the wheel and the tire do not line up perfectly, and air (or nitrogen) escapes accordingly.

Another factor, of course, is cost. Nitrogen-equipped service centers will fill up your tires with nitrogen for something like $10 per tire, which is a far cry from the couple of quarters (if even that) it takes to trigger the air machine at your local gas station. “When it comes down to a dollar decision, it’s hard to argue that spending as much as $40 for nitrogen in a set of tires is a good fiscal move,” writes Jackson.

“Save your money and just keep an eye on your tire pressures,” he concludes.