Friday, February 23, 2007

Don’t Pay for Nitrogen In Your Tires

It’s bad enough that gas stations now make you pay to inflate your own tires with air. But at least you are getting what you paid for…air which does what it’s supposed to do and that is to keep your tires inflated.

Many car dealers are now charging customers to fill their tires with “pure” nitrogen. They tell you that nitrogen does not leak from your tires as quickly as air and this means that your tires will stay properly inflated longer before you have to add more nitrogen (and pay the dealer for this). What the dealers don’t tell you is that the air that is already in your tires is mostly nitrogen anyway. In fact, 78% of the air you breathe is nitrogen. Oxygen represents only 12% of the air. The rest of air includes carbon dioxide and other inert gases. I’m not sure what the purity of the nitrogen is that they pump into your tires for $199 (this is not a typo…one hundred and ninety-nine dollars for filling four tires full of mainly air). But, you can be assured that the purity of the nitrogen is not 100% and is probably closer to the 78% that regular air consists of.

Even knowing all of the above, I have to admit that I was curious about whether or not nitrogen could prolong tire live and improve fuel economy because I knew that NASCAR drivers used nitrogen filled tires and I heard that Volvo’s came from the factory with nitrogen in their tires. I have a BS in Physics from the University of Florida and a Master of Science from Purdue and these kinds of things interest me. So, to find out for myself, my dealership conducted an experiment. We have a fleet of rental cars and we filled two tires of each car with pure nitrogen and 2 tires with regular air. Over the course of many weeks, we measured the pounds of inflation in the nitrogen and air filled tires. There was no difference in the inflations of the nitrogen v. s. the air filled tires. If there is no difference in the inflation, there can be no benefit from nitrogen of better gas mileage or fuel economy.

You may have read my column last week, “Beware the Phony Monroney”. In that column I warned you about car dealers that add a window sticker designed to look exactly like the federally mandated Monroney sticker. This is where you should look for dealer installed accessories and additional dealer markups over MSRP. Often these accessories have a high price but a very low cost. In the case of nitrogen in four tires selling for $199, this is exactly the case. Since air is already 78% nitrogen, it costs virtually nothing to extract nitrogen from the air. To be generous, let’s say the dealer’s cost is $10 including labor. That is a 2000% markup when he charges $199.

Just when I thought I’d seen it all, I actually saw window stickers on a car today from another dealer who had actually modified the Monroney label to show nitrogen filled tires. To do this, the dealer actually had to remove the real Monroney label, make the modification showing the nitrogen tires, and re-paste the Monroney label to the window. Federal law requires that a Monroney label not be removed until the vehicle is delivered to the customer. It also requires that it not be modified. This new vehicle was one we had traded for from another dealer and still had the counterfeit Monroney and the modified real Monroney attached to the window. The modified Monroney looked so authentic, that one of my technicians and my service manager inquired of Toyota about the necessity of our carrying nitrogen tanks so that we could refill these tires with Nitrogen. If this could fool a Toyota dealer’s technicians and service manager, it might fool you too.

This particular dealer also had another charge added to the counterfeit Monroney sticker, a $4,995.00 “Market Value Adjustment”. Most prospective customers think that this is part of the manufacturer’s recommended retail price. They either end up paying too much money for the vehicle or think they are getting more for their trade-in or a bigger discount than they really are. It’s easy to allow someone an extra $5,000 on their trade-in when you have already marked the car up an extra $5,000 over sticker price.


  1. Mr Stewart

    I have been working with N2 tyre inflation for almost 20 years. I have to agree with you on what is a very big deception to the public. Everyone and their uncle seem to be producing N2 harvestors. The problem is that none of these machines actually fill a tyre with the percentage of N2 that would be useful. This is why no noticable difference can be seen when comparing a supposed N2 fill versus a air fill. I have consulted with both Air Products and Air Liquide (free of charge) about what changes would need to be made to the harvestors in order for them to be cost effective. Both companies are not interested in making changes to a machine that will not show large profits.

    Filling a tyre with any pure gas will remove the moisture content of the fill. Any pure gas will expand and contract at a lower rate than air(remember the old rule 1PSI for every 10 degrees F).

    The fact is now with these machines on the market it will actually ruin what are the true benefits of a N2 filled tyre.

    I filled several Michelin tyres with N2, in 1986 and as of 2005 they had not lost any pressure. This is because of the Butyl inner liner that Michelin put onto their tyres. I would like to speak with you about this matter as N2 is unfinished business in tyres. I have more information which I am not willing to divulge on this blog.

    My e-mail is
    tel 713-782-0682

    Thank you and keep up the excellent reporting.

    Peter Dikoff

  2. excellent article.made me change my decision of changing to N2

  3. Purchased 4 new tires at Costco in July of 2006. Costco provided N2 for free when filling the tires. To date I have only had to have 3 PSI added to the right rear tire. I check all 4 tires monthly at home (cold air pressure reading) and have been very happy to date. My only disappointment is Costco does not do this for a flat fee, only if you purchase new tires. As I just purchased a new car, I would love to be able to get N2 into that car as well.

  4. I have to say that you made a mistake in your measurements. You can look at the results of the Consumer Reports study that I cited in my article. They tested virtually every make of tire, filling one with Nitrogen and another with air. There was only 3 pounds difference in the two after ONE YEAR.

    You say that you haven't added Nitrogen or air to your tires for nearly TWO YEARS. Whether you had your tires filled in 2006 with air or Nitrogen, they would have lost so much pressure by now that they would be unsafe to drive on.

    Maybe you have a neigbor that is playing a joke on you. He could be secretly adding air to your tires, leading you to believe that they never lose any pressure.

  5. Nitrogen works and does maintain tire pressures longer. The purity part is around 95 - 96% nitrogen. I will say if a dealer is getting $200.00 for this service and can sleep at night then they are doing well. Our dealership charges only $20.00 for this service and never a charge for refilling or adding. We also only charge $20.00 for this on new vehicles and again never any additional charges.


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