Have you ever seen a car with green valve stem caps?
If so, then you’ve seen a car with nitrogen filled tires.
In fact, you may have a car with nitrogen filled tires sitting in your garage or on your driveway right now.
But what is the truth about nitrogen in car tires?
Is nitrogen filling worth the extra cost? Are there any benefits to nitrogen filling? While some motorists swear by it, others claim that the only thing a nitrogen fill will do is “lighten your wallet” (we have heard one service technician refer to nitrogen filling as a “wallet flush”!)
In this edition of Car Facts we take a look at the pros and cons of nitrogen-filled tires and what you need to know about them.
We’ve researched the top questions that people have about nitrogen tires, and laid out simple answers below so you can determine if nitrogen is right for your car.
Why Are My Tire Caps Green?
Your tire caps are green because your tires are nitrogen filled (or at least were nitrogen filled at some stage).
Tires filled with regular air tend to have black or grey “vale stem caps”, but if you’ve got green caps and you’re wondering why, then it’s because of the nitrogen in your tires.
What Are The Benefits Of Nitrogen Tires?
The main claimed benefits of nitrogen filling tires are:
- Reduced pressure loss – The main benefit of using nitrogen in your tires is that nitrogen will result in a slower rate of pressure loss. All tires gradually lose pressure over time, due to molecules escaping from the tire. However, nitrogen molecules are larger than oxygen molecules, which means they should theoretically take longer to escape out of the minute “pores” in the walls of your tires. This, in turn, leads to more stable and long-lasting inflation.
- Reduced moisture and risk of “rot” – Another argument for using nitrogen in tires is that it helps to reduce moisture inside the tire, lowering the rate at which the tire decays. This is achieved through the process of pumping dry nitrogen into the tires and driving out oxygen and water. The jury is out as to whether there is any real benefit to this for normal use; you’ll be replacing your tires due to tread wear long before they will rot from the inside out.
- Improved fuel economy – This being a consequence of reduced pressure loss – a tire inflated to the correct pressure will improve fuel economy versus an under-inflated tire. If you want to improve the fuel economy of your car, then ensuring the right pressure is definitely an important step to take.
Will Nitrogen Tires Improve Your MPG?
The mere fact of having nitrogen-filled tires on your car will not save you gas or improve your mpg.
The potential MPG and fuel economy gains of nitrogen come from having more consistent, correct tire pressure.
However, if you have correctly inflated tires on normal air (and keep them at the right PSI) and compare that with nitrogen tires at the same correct PSI, then there will be no difference in performance.
What Are The Downsides Of Nitrogen Tires?
The downsides of nitrogen tires are:
- Cost – while you can fill your tires with regular/compressed air for free just about anywhere (most gas stations have tire pumps, for example) you will need to pay for nitrogen filling. This can vary from a few dollars per tire to upwards of $20 per tire.
- Availability of filling options – as per our comment above, you can get regular air in almost any service station in the developed world. However, if you have nitrogen filled tires and want to refill them with nitrogen again, then you will have to find a proper tire shop.
- Limited/conflicting evidence as to the benefits – alongside cost, this is another element to consider. There is very conflicting evidence as to whether or not nitrogen filling provides any perceivable benefit for regular motoring use. It does seem that the benefit for day-to-day usage is rather marginal.
Are Nitrogen Valve Stems Different?
No, nitrogen valve stems are exactly the same as regular air valve stems. The only difference is the cap colour, which is merely to indicate the nitrogen fill.
You do not need green caps for nitrogen either, so if you do fill with nitrogen and lose a cap or want to change them for appearance reasons, feel free to do so.
Do You Need Special Tires For Nitrogen?
No, you can use any regular car tire with nitrogen. From cheap tires through to performance tires, there is no need for special tires for nitrogen filling.
Is Nitrogen PSI The Same As Air PSI?
Yes, 30 PSI (for example) of nitrogen is exactly the same as 30 PSI of air.
The only difference is that nitrogen molecules are larger, but at an equal pressure there is no difference in the “nature” of nitrogen and air PSI.
Will Nitrogen Affect My Car’s Tire Pressure Sensors?
If you have a modern car with tire pressure sensors, then you might be worried that nitrogen will possibly affect the sensors and prevent them from working.
However, you don’t need to worry about this at all – nitrogen will have no effect on your tire pressure monitoring system or its correct function.
Can You Mix Nitrogen And Air In Tires?
Yes you can. It is perfectly safe to fill a “nitrogen tire” with air from a air compressor at a gas station, or foot pump, or whatever you need to use.
Remember that the air we breathe is 78% nitrogen anyway, so filling a tire that was originally nitrogen filled is just going to dilute the “purity” of the nitrogen in the tire.
While diluting the nitrogen in your tires will obviously result in a loss of the benefits that nitrogen brings (to the extent those benefits are actually noticeable in day to day driving) it is certainly no going to cause any harm.
Therefore, if you are out on a road trip or something like that and notice your nitrogen-filled tires need pumping up, don’t be afraid to use regular air as it will not cause any harm whatsoever.
What Happens If You Put Oxygen In Nitrogen Tires?
Nothing bad, you simply lose the claimed benefits of “pure” nitrogen filling (slower loss of pressure and reduced moisture).
In an emergency or due to cost reasons, it is totally fine to put oxygen in nitrogen tires.
Are Nitrogen Tires Worth It?
This is perhaps the most important question of all.
Are nitrogen tires actually worth it?
Realistically, they are not, and are an unnecessary expense for the regular motorist.
Nitrogen tires can make a difference in Motorsport, where anything that gives you even a split second of performance advantage over a competitor is worth the extra investment.
However, if you are driving a car around town, on the freeway etc, you really don’t need nitrogen.
The only circumstance in which we would say it is worth it is if you don’t mind spending the extra money, and you’re the kind of person who cannot be bothered to periodically check their tire pressure and fill their tires with air while at the service station or at home.
Furthermore, you would want to ensure that the place you are taking your tires to have the air swapped for nitrogen will do free refills in the future.
Only if those criteria are met, should you bother considering nitrogen in your tires.
However, in this case you still need to periodically check your tire pressure and have the tires refilled, just potentially not as often.
If you buy a second hand car with nitrogen filled tires, then make a call as to whether the extra investment is worth it for you.
How Much Do Nitrogen Tires Cost?
The price of filling your tires with nitrogen varies greatly depending on where you live, and whether you are getting new tires filled with nitrogen for the first time, swapping air for nitrogen in existing tires, or getting a refill tires already filled with nitrogen.
Prices can vary from nitrogen filling being free (some shops will refill tires that they sold and filled with nitrogen for free as a customer service play) through to upwards of $15 per tire depending on the dealership or service center you go to.
While the cost is not exactly a fortune, it all adds up. If you are trying to save money on your motoring, then you are far better to have air filled tires (filled to the right specification for your car) and then check and re-inflate as required every time you fill your car.
How Can You Tell If You Have Nitrogen In Your Tires?
The easiest way to tell if you have nitrogen in your tires is to look at your tire caps. If they are green, then your tires likely have nitrogen.
If you need to “double check” then a tire shop will be able to do this for you. However, in the first instance simply look out for the green caps.
Can You Check The Pressure Of Nitrogen Filled Tires?
Yes, you can – and you should!
While one of the arguments of nitrogen filling is that it reduces the rate of “natural loss” of pressure in your tires, it is important to periodically check nitrogen filled tires anyway.
Having incorrectly-inflated tires can lead to reduced fuel economy, worse tire wear, and even altered handling and safety characteristics.
Just because you have nitrogen, it doesn’t mean you should never check your tires.
Do You Need A Special Tire Pressure Gauge For Nitrogen Tires?
No, you can use any tire pressure gauge with nitrogen – you do not need a special one . We always recommend investing in a quality gauge that you can keep in your car, so that you can get accurate and dependable pressure readings.
View our guide to recommended tire pressure gauges here.
Why Do Aircraft Tires Use Nitrogen?
One of the arguments we have seen for the use of nitrogen tires is that aircraft tires are filled with nitrogen, and if it is good enough for the highly-regulated world of aviation, then it must be good enough for your car.
So, why do aircraft tires use nitrogen?
Basically, because nitrogen is less likely to expand or contract due to temperature changes and high pressure loads that can be placed on an aircraft during takeoff and landing.
Water droplets that exist in air can vapourize (i.e. turn to gas) due to the heat generated by tires during take off and landing, owing to the extreme forces exerted by the aircraft and the speed at which it is travelling.
Plane tires run at high pressures anyway, and even the smallest deviation in pressure (such as additional pressure from water droplets turning into gas) can risk causing explosions or other problems, which can have disastrous consequences.
Tragically, there has been at least one documented case of plane tires being filled with air instead of nitrogen causing a crash.
Mexicana Flight 940 crashed on March 31, 1986 with the death of all 167 occupants due a center landing gear tire being filled with compressed air instead of nitrogen.
An overheated landing gear brake caused the air-filled tire to explode (as the water droplets turned to gas) which ruptured important systems on the plane and led to a loss of control.
One thing to note is that not all aircraft tires are filled with nitrogen. “General aviation” aircraft (e.g. planes used for personal use) are often filled with air.
Bear in mind that planes operate in far more challenging conditions than cars do; just because nitrogen is important for plane safety and performance, doesn’t mean it is a requirement for cars.
Are Nitrogen Filled Tires A Gimmick?
Ultimately, we think that nitrogen filled tires are a gimmick.
Unless you have a specific need (i.e. high performance track driving) it probably isn’t worth the extra money.
For race driving, nitrogen is worth it and not a gimmick as anything that provides even a fraction of a second’s advantage per lap (due to consistent tire pressures and temperatures) is going to make a big difference.
However, for the average motorist you are better to put the savings towards a good tire pressure gauge, and then check your tire pressures regularly and inflate them.
Any of the benefits of nitrogen filling can be had with regular air by checking and properly inflating your tires on a frequent, consistent basis.
Conclusion – Are Nitrogen Tires Worth It?
Hopefully this article has helped you to understand whether nitrogen tires are worth it for you, as well as the pros and cons of using nitrogen.
We welcome your feedback as well. Are you a a fan of nitrogen in tires, or do you believe it is a waste of money?
Let us know in the comments below.
4 thoughts on “Nitrogen Tires – Your Questions Answered”
Even when you fill a tire with 99.999999% Nitrogen from a cilinder , there is still the 1.013bar/ 14.7psi normal air inside the tire.
Its possible to fill and let out all the gascompound, and fill again with Nitrogen, to come close to 100% Nitrogen filling in tire, but this is not done in practice, and first vacuüm the tire is not done because it damages the tire.
Then Oxigen difuses out of the tire ( or even into the tire) 3 times as fast as Nitrogen, not only by the sise of the molecule, more factors play a part .
But because 4 times as much nitrogen then oxigen in air, more Nitrogen then oxigen goes out in the same time.
And then only in the beginning.
In the long run, the partial pressure of oxigen will be the same as outside air , 0.2 bar/ 3 psi and then yust as much oxigen goes into the tire as is going out.
Look up Daltons law for that.
Very interesting, thanks for the comment!
Personally, I never saw the value in using nitrogen in tires as I I have always been pretty good at maintaining my vehicles. Then I purchased new tires at Costco four or five years ago and They fill the tires with nitrogen.
Sure enough, as fall rolled around we had one of those big drops in temperature typical for the season. Soon after I kept hearing “dad my tire pressure light is on “and “Hon my tire pressure light is on “several times over. So I would dutifully go out and fill all of my kids and my wife’s tires to the appropriate setting. But amazingly, my truck tires were just fine. I am now sold. If my tire pressure gauge light comes on it means that I have a nail in my tire.
Costco now has free nitrogen refilling stands in their parking lots. You cannot fill an empty tire, but I routinely check to make sure my tire pressure is good. If it is free, I definitely recommend it
Thanks for your comment Richard.
As you say, if it’s free there is no reason to say no. For example many tire shops seem to do free nitrogen fills on new tires etc. In that case there is no downside to taking it (as you can always fill with “normal” air in an emergency)