Should You Fill Your Car's Tires With Nitrogen?

Should You Fill Your Car's Tires With Nitrogen?

The Green Cap on Your Tire Could Take Green From Your Wallet


A member of the Dodge Challenger owners' forum was buying a new car from a dealer and noticed green valve-stem caps on all four tires. The salesman told him that the tires had been filled with nitrogen, which would keep the tire pressure and temperature more consistent and that it would prevent tire rot from the inside out. It wasn't a free add-on, though. The "nitrogen upgrade" was a $69 item on the supplemental window sticker. Another forum member later posted that his dealer was charging $179 for this same "upgrade."

Some dealerships and tire stores claim that filling your tires with nitrogen will save you money on gas while offering better performance than air. But a closer look reveals that nitrogen has few benefits and much higher costs. For starters, a typical nitrogen fill-up will cost you about $6 per tire.

Why Nitrogen?
The Get Nitrogen Institute Web site says that with nitrogen tire inflation, drivers will note improvements in a vehicle's handling, fuel efficiency and tire life. All this is achieved through better tire-pressure retention, improved fuel economy and cooler-running tire temperatures, the institute says.

This sounds great in theory but let's take a closer look at each of those claims.

  • Better tire-pressure retention: Over time, a tire will gradually lose pressure. Changes in temperature will accelerate this. The general rule of thumb is a loss of 1 psi for every 10-degree rise or fall in temperature. The institute says that nitrogen has a more stable pressure, since it has larger molecules than oxygen that are less likely to seep through the permeable tire walls.

    In 2006, Consumer Reports conducted a year-long study to determine how much air loss was experienced in tires filled with nitrogen versus those filled with air. The results showed that nitrogen did reduce pressure loss over time, but it was only a 1.3 psi difference from air-filled tires. Among 31 pairs of tires, the average loss of air-filled tires was 3.5 psi from the initial 30 psi setting. Nitrogen-filled tires lost an average of 2.2 psi from the initial setting. Nitrogen won the test, but not by a significant margin.
  • Improved fuel economy: The EPA says that under-inflated tires can lower gas mileage by 0.3 percent for every 1 psi drop in pressure of all four tires. The theory is that since nitrogen loses pressure at a slower rate than air, you are more likely to be at the correct psi and therefore get better fuel economy.

    If you are proactive and check your tire pressure at least once a month, you can offset this difference with free air, and you won't need expensive nitrogen. We think this invalidates the "better fuel economy with nitrogen" argument.

    For many people, however, this kind of maintenance is easier said than done. Most people either forget to regularly check and top off their tires, or never learned how to do it in the first place. Even Edmunds employees (typically a pretty car-savvy group) were under-inflating or over-inflating their tires, according to a tire-pressure study we conducted a few years ago.

    And though tire-pressure monitoring systems (TPMS) now come standard on cars, a 2009 National Highway Transportation Safety Administration (NHTSA) study found that only 57 percent of vehicles with TPMS had the correct tire pressure. That's because most systems are only meant to signal that a tire has very low pressure, not to show that the pressure is optimal.
  • Cooler running temperatures: When air is pressurized, the humidity in it condenses to a liquid and collects in the air storage tank you use at the local gas station. When you add compressed air to the tire, the water comes along for the ride. As the tire heats up during driving, that water changes to a gas, which then expands, increasing tire pressure. Because nitrogen is dry, there is no water in the tire to contribute to pressure fluctuations.

    But this fluctuation in temperature isn't as significant as you might think. A 2008 ExxonMobil study plotted the changes in temperature over the course of various inflation pressures. The lines on the graph were virtually on top of each other. In other words, the change in temperature when using nitrogen was negligible.
  • Prevent wheel rot: Nitrogen proponents will also point out that water in a tire can lead to wheel rot. A tire engineer who anonymously maintains Barry's Tire Tech, a blog on a number of tire issues, says this isn't really a problem with modern cars.

    "Alloy wheels don't really have a problem with water inside the tire," the engineer writes in a post on nitrogen inflation. "They are coated to keep aluminum from forming aluminum oxide, which forms a crust, which isn't very attractive. But even then, this crust protects the aluminum from further corrosion from the water."

    Where wheels have problems is when the aluminum alloy contacts steel, such as the steel spring clip used on wheel weights. It's a particular issue when salt is present, the engineer writes. "But this problem is totally independent of the inflation gas," he says. "Steel wheels only have a problem if the paint is damaged."

Cost and Convenience
Let's say a person bought a set of tires at Costco, a place that uses nitrogen to fill all the tires they sell. If he needs to top off the tires with more nitrogen, he won't be able to go to just any gas station. He can use regular air if there is nothing else available, but that would dilute the nitrogen in the tires. He'll have to go back to Costco and wait until the tire technicians can attend to the car. On a busy day, he could be there awhile.

Nitrogen is free at Costco and at some car dealerships we called, but these are rare cases. We called a number of tire shops that carry nitrogen and found that the prices for a nitrogen fill ranged from $5-$7 per tire. Assuming our consumer was diligent about checking his tires monthly, he could potentially spend about $84 a year on nitrogen alone per tire. Compare that to the most gas stations, where air is free or a 75-cent fill-up for all four tires at the most.

Finding tire shops with nitrogen could be an issue, too. We called a number of large chains, including America's Tire Co., Discount Tire and Walmart. None carried nitrogen.

Is Nitrogen Worth It?
The air we breathe is made up of 78 percent nitrogen, 21 percent oxygen and a few other elements. To get the desired benefits for tires, nitrogen needs to be at least 93 percent pure, according to nitrogen service equipment providers quoted on So we're basically talking about adding an extra 15 percent of nitrogen and getting rid of as much oxygen as possible.

Based on cost, convenience and actual performance benefit, we don't think nitrogen is worth it. A much better use of your money would be to buy a good tire-pressure gauge and check your tires frequently. This is a good idea even if you have a tire-pressure monitoring system in your vehicle. The warning lights aren't required to come on until you have less than 25 percent of the recommended tire pressure. Having the correct tire pressure will get you many of the benefits of using nitrogen and will ensure that your tires last longer.

To find a dealership that knows how to treat shoppers right, please visit's Dealer Ratings and Reviews.



  • Costco has a nitrogen air line available next to the shop so it's not only free, but convenient to use if you live near a Costco. I think it's worth it to fill up air there once a month since I get gas there too.

  • colin1000 colin1000 Posts:

    Unless the dealer is using a vacuum pump to remove the air from the tires before filling with Nitrogen there will be a good percentage of the original air left in the tire so you do not get 100% Nitrogen by any means.

  • himileage himileage Posts:

    In support of the article, consider this also: we have two options, Fill with air (78% Nitrogen, or N2) vs Fill with 100% N2. If the theory is true, the tire filled with air will leak all the non-N2 molecules, while the 100%N2 filled tire does not leak. This would imply that rubber is acting like a molecular sieve, preferentially allowing the non-N2 gas molecules in the air to escape. But, since the theory says that the N2 cannot escape, only N2 should be left in our leaker after all the Non-N2 molecules(oxygen, argon, CO2, etc) escape. Once this happens, you have a low tire that is @78% of full volume and is filled with pure N2. So you fill it back up with air, 78% of which is pure N2. And now you have a tire with 78% volume fill@100% N2 concentration, that has been topped off by adding back the lost 22% of volume with air that is 78% pure N2 and 22%'impurity'. So how much impurity is now in the tire? It is 0.22(22% of total volume) X 0.22(22% impurity in air)=0.0484, or 4.84% of the total volume that is now Non-N2 molecules in the tire. This small amount of impurity should then escape and the process repeats, but on the next go, you wind up with only 1.06% impurity. So you started at 22%, then went to 4.84%, then down to 1.06% Each drain/refill cycle the amount of total impurity drops, until after a half dozen adjustments, you are left with only ~0.01% impurity in the tire. So why do Mfr's bother? My hunch-- and that's all this is-- is that in the extremely automated world of auto manufacturing, they want consistency from vehicle to vehicle and they probably run automated tire fill processes. Now when it comes to consistency, all Detroit jokes aside, they STUDY this stuff at a level where most of us could not even comprehend the math. And since compressed air systems are notoriously oily(contaminant), with variable moisture content dependent on atmospheric conditions when the air was compressed, maintenance conditions on drying equipment, etc, they probably got some inconsistency in results that they did not like. So for January-built cars to be the same as August-built cars, the results of automatically filling a tire are more consistent if the mfr just buys commercial grade N2. Commercial N2 is oil free, dry, and reasonably pure so every vehicle built gets a more precise/consistent fill with almost no contaminants. And if using pure N2 slows the pressure loss rate on a scale of hundreds of thousands of cars, then that's probably a good (albeit infinitesimally small) thing for the country from an oil consumption standpoint.

  • bwms1 bwms1 Posts:

    I maintain some cars for my work, we have 2 brand new Expeditions and other new vehicles. Guess what? The Nitrogen tires do nothing, when it gets cold, the low pressure light still comes on and they need a top-off. It has happened with me personally (2 new vehicles) and with work vehicles. Nitrogen tires are a SCAM. Just keep track of your tire pressure, and make the dealer remove the charge when you buy a new car. Some charge up to 200 bucks! Dealer are not your friends.

  • rusty_tank rusty_tank Posts:

    I have had N2 in my tires since I purchased them 3 and a half years ago and I have only had to add air when I got a nail stuck in one of them. For the first 3 months I'd check the pressure every time I filled up my gas tank, with 0 change in psi, I started checking them less and less, only 1 to 2 psi max difference in pressure from when I had them installed. I suppose that different tires may have different results given that manufacturing and materials may vary, but I'm a believer in N2 if only for the idea that I don't ever have to fill up my tires again. One other note is that I live in the south so when it gets cold it's not supper cold. For the extra 20$ I paid when I had them installed I feel like it was worth it.

  • I am not satisfied that the methodology used in the 2007 Consumer Reports article represents a typical daily drive, but even using their data, a 50% difference in air loss is significant. A 0.6% difference in mileage over a typical 15k mile year at $3 or more per gallon is more than enough all by itself to justify the average cost of about $7 per tire. Real world fleet tests have found that air filled tires lost 1 PSI or more per month with pickups, vans and SUVs losing up to 2 PSI per month while 100% nitrogen filled tires lost 1 PSI every 4 months regardless of vehicle type. The NHTSA says that 30% of all vehicle in the US have at least one tire that are under-inflated by 6 PSI or more. The NHTSA survey you quoted found that most people check the air in their tires only when the vehicle goes in for service or when they have a problem with the tire. It came out to an average of every 4 months. The survey found that those that indicated they did their own oil changes and minor service checked the air in their tires even less frequently compared to those that took their vehicles in for service, an average of every 7 months. Over a year a typical passenger car tire will lose 9 PSI in city driving. If you spend more time on the highway with your tires heating up much more from the friction of higher speeds, then that air loss will be even more pronounced. A single 300 mile trip at highway speeds in a passenger vehicle will result in an average air loss of 2.1 PSI according to the US DOT. TPMS equipped cars account for 16.9% of passenger vehicles on the road in the US as of the end of 2013 and the majority utilize indirect TPMS that cannot directly measure air pressure. Most work on wheel rotational speed. That is why they only inform you that your tire may be significantly under-inflated. Under-inflated tires are the #1 cause of tire failure according to the NHTSA. That alone is enough reason to use Nitrogen. How many tires do you have to replace to account for a $7 per year nitrogen cost? One major reason for tire failure is oxidation. As your tire heats, the oxygen in the air reacts with the compounds in the tire and oxidation occurs. This oxidation effects the seal, not the wheel, it increases the porousness of the tire wall and hastens air loss. There is no oxygen in 100% N2 filled tires. I could go on with the studies, but the bottom line is at an average of $7 per tire, nitrogen is well worth the cost.

  • stever stever Posts:

    Good points, @richardburns. In theory, tire pressure monitor sensors would cover most of your issues. In real life, few TPMS systems offer real time read outs of each tire and many only illuminate the idiot light when the psi falls to a preset amount. Meanwhile you are driving around on tires that aren't optimally inflated.

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