That was I question I received from a friend who reads this blog. Further he mentioned that he had been told that nitrogen would:

• Not leak like compressed air does
• His vehicle would get better gas mileage
• Perform better because race cars use nitrogen
• Be safer because airplanes use nitrogen
• The tires and wheels would last longer

I’m not a scientist but was once considered a tire industry expert before I retired. So we need to first look at the difference between compressed air and compressed nitrogen, and then recognize who is advocating nitrogen filled tires. We will also explore the answers to the bullet points above.

Nitrogen is, well, nitrogen. When installed in a tire that is already filled with air, the air has to be purged before nitrogen is added. This isn’t just releasing the air but removing it.

Compressed Air is Mostly Nitrogen

Oops. Dry air is 78% nitrogen already. Also almost 21% oxygen, and some other trace gases. At sea level, about 1% of air is water vapor, decreasing as one goes up in altitude.

Won’t Leak Like Compressed Air Does

Nitrogen doesn’t leak out of a tire as much as air does. Tires are slightly porous and over time both nitrogen and air will leak out. Because nitrogen molecules are slightly larger than oxygen molecules, tires filled with compressed air will loose tire pressure a little more quickly than a nitrogen filled tire. So what is the difference between the two? How much more air will leak out?

About 10 years ago Consumer Reports did a study. They took 30 tires already mounted on wheels and left them outside for a year. The tires had been taken off some test vehicles that had been used for simulated driving experiments in a lab. All the tires had around 16,000 miles on them and had been in service under the almost exact conditions. All the tires were set to 30 psi. After a year the nitrogen filled tires has lost an average of 2.2 psi per tire, the air filled tires 3.5 psi on average. A difference of 1.3 psi over an entire year.
We can point out that the tires were not driven and subject to real-world road conditions, a test that would have been difficult and expensive to perform.

Tire manufacturers and a vehicle’s Owner Manual usually recommend that tire pressures should be checked once a month. If a nitrogen tire is low, the owner will need to locate a shop that can add nitrogen. Compressed air is available almost everywhere. So you would be better off to buy a quality tire gauge instead of spending a bunch of money for nitrogen. Plus you can use the tire gauge on any vehicle you choose.

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An example where nitrogen availability would be problematic is when we go camping in the summer. We live in a desert and often the overnight low is 90F. When I check the tires prior to a trip, I often add a couple extra pounds of air in each tire above the manufacturer’s cold inflation specification. We have 8 tires between the tow vehicle and the trailer. If we are camped in the Sierra Nevada for a few weeks, where the overnight lows can get into the low 40’s at times, I often find that our cold pressure (yes I check the tires before leaving) can be 5 PSI below the manufacturers’s specifications. Tire pressure increases and deceases as the ambient temperature changes. We may drive through the desert on the way to the mountains in 120F weather and the hot asphalt makes the tires even hotter. With the cold nighttime mountain air, we are looking at almost an 80 degree differential. How would I add nitrogen at the campsite? I don’t want to drive down a winding mountain road with low tire pressures. So I add air to the tires with this portable compressor:

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Now retrieving the rating.

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Vehicles Get Better Gas Mileage with Nitrogen

This thought comes from the idea that tires lose pressure over time and air filled tires lose more than nitrogen. This is true. However if you check your tire pressure once a month, it won’t happen. The tire doesn’t care what kind of gas is in it. Pressure is the only determinate of how a tire will affect gas mileage.

Race Cars Perform Better Because they Use Nitrogen

This is true also – with qualifications. Some claim that nitrogen doesn’t expand as much when a tire gets hot. That is not true. Boyle’s law tells us that gases in a fixed vessel (the tire) and a fixed pressure react exactly the same when temperatures change.

Race cars operate under conditions that none of us will ever approach in our cars and light trucks. The slightest change in pressure in any tire is not a good thing on a race track. The benefit of nitrogen versus compressed air is primarily that there is some liquid in compressed air.

Remember I mentioned air at sea level is 1% water vapor? This is why nitrogen works better in a race car. 1% doesn’t seem like a lot, but it is.

Over the years I have used many industrial air compressors. If the oil is changed when recommend and the air drained each night, these compressors can last 30 or 40 years. They won’t if they aren’t drained each night. A lot of water drips out when the tank is drained. At home I have a 33 gallon air compressor. After each use I turn it off and drain the tank. There is always a tiny puddle of water on the floor after the compressor drains.

You won’t gain any noticeable performance improvement with nitrogen in your car, light truck, or camper tires.

Be Safer Because Airplanes Use Nitrogen

Airplanes use nitrogen to reduce any potential fires should the tire explode, especially during landing. Both nitrogen and oxygen are not flammable. Oxygen is a gas that can readily oxidize with other materials and then cause a fire if a spark is present. Should a tire blow with sparks in the area around other combustible materials, you will have a fire and a big one if there is a lot of oxygen available. This is why there are always warning signs not to smoke when bottle oxygen is in the vicinity.

The Tires and Wheels Will Last Longer

Nope.

Here the thought is that water in compressed air will degrade the wheel and the inside of the tire. I have never seen this happen in a tubeless tire. Almost all tires’ treads wear out before the sidewalls. An exception is when a vehicle is rarely driven. After several years, think 7 or more years, the outside of the tire will begin to noticeably degrade due to exposure to UV and smog.

I have removed tires from wheels that have seen hundreds of thousands of miles of use (a few with over a million) and the inside of the wheels look just fine.

This wasn’t necessarily true decades ago when we used tube-type tires before tubeless tires became common. The tire/wheel combination wasn’t leak proof, especially where the bead was in contact with the wheel. The tube inside the tire contained the compressed air. It was common for water to get inside the tire between the tire and the tube, and between the wheel and the tube. This wasn’t water vapor; it was a lot of water. So yes, years ago the inside of the tires could degrade quickly and wheels could rust-out.

So Who is Advocating Nitrogen Replacement?

Why of course, it’s the nitrogen equipment makers and the shops that repair cars and sell tires. Every year cars are more reliable and the required maintenance work are decreasing, while the required intervals are increasing. Shops are running out of work. Nitrogen is called an “up sell” or an “add on sale” and it is very profitable. Some large outfits can recoup their equipment costs in a few months and unskilled workers can do the job. It’s all about profit and there can be a lot of profit selling nitrogen tire fill service.

Is Nitrogen Better?

Yes it is.

But here’s the caveat – if you check your tire pressure every month they are almost equal. I don’t know of any tire company that recommends nitrogen (there may be some) as the best option. Some do come to the same conclusion as me, and say it is marginally better if you want to spend the money, but it is not necessary.

At the beginning of this post I inserted a picture I found Discount Tires’ website. I like this company – a lot. In California their stores are called America’s Tire. Their stance is the same. They will fill your tires with nitrogen if you request it, but they don’t market it, nor do they try to “up sell” customers. In fact, their marketing includes the message that they will check your compressed air filled tires for free, whether you bought the tires from Discount Tire or not.

If you want to spend the extra money, go ahead. It’s simply a personal decision. Plus your green valve stem caps will look cool and tell the world you spent a bunch of money for nitrogen. You can even post pictures of you caps on Facebook or Instagram 😉