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Is Nitrogen Better Than Air for Tires?

I have had to lower my estimate of the quality of LiveScience.com. It is generally a straightforward science news outlet, but some recent articles have shown me that they have an insufficient filter in place and need more quality control. The worst abuse is their Top Ten Unexplained Phenomena (I’ll tackle that next week).

A more subtle problem, however, are articles that sound superficially reasonable but are actually just thinly disguised advertisements. Even more insidious is the habit of reprinting press releases without doing further investigation. This is an easy way to bulk up an online news feed. Some sites do nothing but aggregate press releases – and that’s fine, as long as it’s obvious that is what’s going on. But many sites also reprint press releases as if they were written by a science news reporter. Press releases are not always the most objective or even accurate reporting on a scientific discovery.

This article from LiveScience seems to be one that was spoon-fed to the reporter, Trey Granger, who did not give any evidence of doing any independent digging. The story is about filling tires with purified nitrogen instead of regular compressed air to improve gas mileage and extend tire life. Granger did not question any of the claims of the company selling the nitrogen system – the readers who left comments did a better job of asking questions.

There are several approaches to a claims like this – common sense, testing the underlying claims, and testing the net effects.

From the common sense point of view – how do the claims jibe with logic and basic scientific facts – the claim that purified nitrogen in tires will make a significant difference seems dubious. Air is already 78% nitrogen, the rest is oxygen with some carbon dioxide, water vapor, and then trace gases. The specific claim is that oxygen leaks out of tires faster than nitrogen. This may be true, but it seems unlikely to be significant.

Let’s take a look at some of the specific claims in the article:

1. Nitrogen makes up almost 80 percent of our air, making it a naturally-occurring element that we’re exposed to every day
2. Because it is a dry gas, nitrogen is more stable than oxygen and will cause less leaks and rust
3. Nitrogen lasts longer in your tires (up to six months without a top-off), allowing you more leeway with tire pressure
4. You can expect up to 30 percent better tire wear if they are properly inflated with nitrogen, meaning less tires to dispose of (use Earth 911 to find out where to recycle tires near you)
5. Nitrogen can also be used to fill non-car tires, so you can improve the life of bicycle and motorcycle tires

You see how it reads like an advertisement, not science reporting. Nitrogen is naturally-occurring? First – so what? Second – so is oxygen. Nitrogen is a dry gas? What does that mean? Is this a clumsy way of saying that purified nitrogen has the water vapor removed? Three and four are the actual claims (the first two were just lame sales-pitches, the kind of dubious things that companies use to increase the list of supposed benefits of their products). And five, again, is just a sales pitch.

What about the actual claims? The first claim is that nitrogen lasts longer in tires than regular air. This is not an end in itself but is the supposed mechanism by which cars will get better mileage and have longer lasting tires. This claim was tested by Consumer Reports. After one year they found that tires filled with regular air lost 3.5 psi from a starting point of 30psi, while nitrogen filled tires lost 2.2 psi. That’s a difference of 1.3 psi over one year – which hardly seems significant.

The report of the study left many questions unanswered, such as how the tires were used over that year, if at all, but I did note that Consumer Reports filled and emptied the tires with nitrogen three times and then measured the nitrogen to make sure they had 95% nitrogen. This is a good method to test the effect of 95% nitrogen in the tires, but it may not be a good test of the real world use of nitrogen tire filling systems. I doubt the average user, even at a garage, will be so fastidious.

The removal of water vapor, according to all the car sites I checked, can reduce the expansion and contraction of the air inside the tires with heat and cold, and therefore maintain more even tire pressure. This can matter to a race car, where minute changes in tire pressure will alter the handling of a high-performance car racing at tremendous speeds around a track. This is insignificant to a consumer on the road.

What about the net effects of this small advantage to nitrogen (assuming the Consumer Reports tests are accurate)? The New York Times did an article on this question – this was not a formal study but a informal trial conducted by car dealer, Earl Stewart, who used the nitrogen system for eight months in some of the tires he placed on his cars. He found minimal differences in wear and tear on the tires, and switched back to regular air.

The Bottom Line

Pure nitrogen in car tires seems like a waste of money and probably a net disadvantage. It costs about $10 a tire when purchased to have them filled with nitrogen. If you want to keep them filled with nitrogen you then have to find a shop that has the equipment, or you can purchase the aerosol refill cans – adding extra expense.

The advantages to tire pressure are insignificant to the consumer driver on the road. In fact, I think such a system would be a net negative, and here’s why. Far more important than what your tires are filled with is that they are kept filled. Keeping tires properly inflated can improve gas mileage, on average, about 10%. This is far more of an effect than all the so-called green technologies that are increasingly popular.

Filling one’s tires with nitrogen may lead to a false security and therefore decrease vigilance about checking tire pressure. Also, difficulty in finding a station to refill the tires with nitrogen may delay refilling the tires – it can be an unnecessary barrier to filling tires properly.

Tom and Ray over at CarTalk (I love those guys) say:

So, none of these advantages is important to the average driver. They just don’t matter enough to ever think about. And they certainly don’t matter enough to pay for, Rob.

(They were answering Rob’s question)

Nitrogen for tires seems like a overly complex and expensive solution to a problem that is much more easily, cheaply, and effectively fixed by simply checking your tire pressure regularly. In fact, checking your tire pressure will do more for you gas mileage than all the fancy hybrids, alternative fuels, and other high-tech solutions (at least for now). While we’re at it – keep unnecessary items out of your car. Just taking that 20lb box of magazines you were going to recycle out of the trunk will improve your gas mileage more than nitrogen in the tires.

As for LiveScience – they get three thumbs down for their reporting of this topic. Trey Granger did not appear to spend even 5 minutes on Google seeing what is already published on the topic.

15 comments to Is Nitrogen Better Than Air for Tires?

  • Drum Billet

    I’m surprised they haven’t removed the article.

  • togamonkey

    For everyday normal cars, I completely agree. However, I used to work at a science museum that had a NASCAR section. I seem to remember that NASCAR uses nitrogen in their tires so that when the tires heat up, the water vapor doesn’t expand a bunch and change the tire pressure. Tire pressure for something going as fast as those cars do is something that can affect performance, so they use nitrogen to make the tire more consistent.

    It was actually a pretty interesting section. You don’t hear about the “Science of NASCAR” too often.

  • You’re right, sounds like a bunch of hot air to me.

  • I write press releases for the computer industry sometimes. (I work for a software company.) It’s always weird when a magazine published my release verbatim as a news story. Better publications (I’ll mention Network World) actually read the release and have someone check whether our products really do what I said they can do. They can, I’m not a liar, but they should check.

  • I was happy to see this topic since I blogged about it a few days ago and, while writing it, I was wondering what NESS and the rouges at SGU might think of it.

    I’m glad we came to roughly the same conclusion: while there’s some benefit, it isn’t worth paying for.

  • moopet

    Personally, I think they should take down the article until they learn the difference between ‘less’ and ‘fewer’ as that was painful to read.

  • HCN

    When I was doing structural analysis on landing gear many eons ago, I was told that jet aircraft tires were filled with nitrogen to reduce chances of fire.

    Now if you regularly drop your car on asphalt while screaming along between 100 to 200 knots (the latter velocity is hopefully only done during new design flight test), then you might have a valid reason to fill the tires with nitrogen. Which is perhaps why NASCAR uses nitrogen in their tires.

    Thing about it: oil based tire material + oxygen (in air) + heat at high speeds = fire

  • DLC

    Nascar.com confirms that the teams use “dry air or nitrogen”.
    http://www.nascar.com/news/features/tires/index.html

  • russ

    i stumbled onto the LiveScience store via a banner ad recently. they do have some odd stuff on there:

    Biblical Garden Terrarium
    http://livesciencestore.com/56812.html

    …and not particularly science related spying equipment!
    http://livesciencestore.com/57837.html
    http://livesciencestore.com/57766.html

  • dcardani

    Steve, can you elaborate on what you mean by this comment:

    “In fact, checking your tire pressure will do more for you gas mileage than all the fancy hybrids, alternative fuels, and other high tech solutions…”

    I don’t understand what you mean. If I drive a 30 MPG car, making sure my tires are properly inflated will get me to 33 MPG according to your statement. (10% better, right?) But if I buy a new Prius, for example, Toyota claims it gets at least 45 MPG. I’m probably misunderstanding what you mean, but it seems like buying a hybrid would significantly help in this case.

  • Steven

    First, let me warn you that I work for a company that is involved with nitrogen tire inflation, so I may appear biased. I believe in nitrogen tire inflation, not only because of the benefits to the consumer, but the environment as well. I run a blog dedicated to nitrogen tire inflation located here:

    http://tirenitrogen.typepad.com/tirenitrogen/

    I wanted to address, in depth, some of the issues you mentioned in your informative post, but for the sake of brevity I will respond to a couple, and tell people feel free to visit my blog if you would like more information.

    You say that people should just check their tire pressure regularly and they would see the same effects. I agree, topping off tire pressures regularly would help. But, as NHTSA notes, 85% of Americans do not check their tire inflation pressure regularly, and 30% are driving around on a significantly underinflated tire (25% or greater). American Consumers are busy, and most dont have (or take) the time to spend 10 minutes checking tire pressures and topping off accordingly.

    Not even the tire companies dispute that nitrogen inflated tires maintain pressure significantly better than air filled tires. Maintaining proper tire pressure is a major benefit to 85% of the general public, because it helps them remain closer to the recommended pressure between service visits. While consumers can minimize underinflation by checking their pressure regularly, it is common knowledge that most do not. And Nitrogen helps these consumers.

    I will not dispute the findings of the Consumer Reports test, only say that they were based on static tests where the tires were not in operation. Dynamic tests performed by Bridgestone show signicantly better numbers.

    Also, you are correct. Nitrogen is dry, and that does mean that the water vapor has been removed. I will let Bridgestone, a tire manufacturer who has done extensive nitrogen research, comment on the benefits of this (as well as better tire pressure retention) in an article located here:

    http://tirenitrogen.typepad.com/tirenitrogen/files/BridgestoneReprint.pdf

    As for your claims that most tire shops wont be diligent enough to fill a tire 3x, I disagree. Most equipment offered automatically purges and fills the tire, usually 2x, and provides a minimum tire purity of 95% nitrogen. This is an automated process that takes about 10 minutes or less on the average car.

    Other benefits that are worth mentioning: It has been proven (by Bridgestone and Ford) that nitrogen nearly stops the aging of the rubber in tires, and that the rubber with a nitrogen filled tire is as strong after 2 years as an air filled tire after 10 weeks. Also, underinflation in the USA on cars and light trucks yields to 1.2B gallons of wasted fuel annually. This increases greenhouse gas emissions and does unnecessary harm to the environment.

    My contact information is on my blog, and I could discuss this information further if anybody is interested.

  • dcardini,

    In your example you are getting better gas mileage by going to a smaller, lighter car. Of course, if everyone trades in their trucks for mini’s that would have a huge impact.

    The question is – how much is the hybrid technology adding? In other words, if you had a Prius – same size, shape, weight,etc. – but removed the hybrid technology (the batteries and electric engine) what would your gas mileage be? Let’s say you beef up the engine a bit to make it powerful enough to get by without the boost from the electric engine. I don’t know if there is an exact answer to this – but I have read many analyses that suggest the hybrid technology is not adding much – and if you live in a cold environment or do a lot of highway driving, it can be a net negative.

    In other words, if we keep the size of the vehicles the same (and other variables like safety features, etc.) and only either convert to hybrid, to flex-fuel, or properly inflate the tires – you are probably better off just inflating the tires.

    This, of course, will change as the new technologies improve.

  • Wow, this old chestnut is still doing the rounds! I thought it got well and truly trounced years back, along with the daft ‘deer’ or ‘kangaroo’ warning whistles…

  • jlucidi,

    Thanks for the detailed comment and for disclosing your potential conflict of interest.

    Actually, what you are saying is factually not different than what I wrote – there are advantages to nitrogen. We disagree on interpretation – all the non-biased sources I read concluded that the advantages are not significant for the average consumer.

    I note that the Brdigestone link you provided is for truck tires – they are talking about trailer rigs, not sedans. For race cars and large commercial trucks, nitrogen may make sense and be cost effective. That says nothing about the average consumer driver.

    I understand the point about the fact that even though people should keep their tires inflated, they don’t. This is similar to many debates we get into in medicine – people should just eat a balanced meal, but they don’t. But this does not address the underlying question – is the advantage sufficient to be worth it.

    Also – for this issue, I think there simply is a severe lack of pulic awareness about the effects of tire pressure. Sometimes in medicine the solution is not a new dubious intervention, but a public education campaign. Perhaps we just need to educate the public more about maintaining tire pressure and generally keeping cars fuel efficient, rather than just using a technology with marginal benefits.

    To further the medical analogy – we are better off changing life styles than having people take a pill with their fat-laden high calorie meal.

  • Belgarath

    Hi Dr. N,

    Transport Category aircraft tires are generally filled with dry nitrogen. (Actually, aircraft that are certified above a certain maximum takeoff weight are REQUIRED to use Nitrogen)

    There are really only two reasons for this:

    1) The expansion and contraction of the gas in the tire. Essentially aircraft tires are subject to extreme variations in external temperature and pressure. Filling with dry nitrogen helps with this and also it slows the degradation on the internal components of the tire.

    2) If a tire fails, the surge of inert nitrogen gas helps to keep the danger of fire down. Aircraft tires have blow-out plugs to prevent catastrophic failure. When you brake hard, you build up a lot of heat. This can actually start the tire burning, but since the interior of the tire is filled with nitrogen and very little oxygen, the fire can’t really get going.

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