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Should You Fill Your Car's Tires With Nitrogen?

Edmunds.comEdmunds.com Posts: 10,059
edited November 2014 in General
imageShould You Fill Your Car's Tires With Nitrogen?

Some car dealerships and tire chains claim that filling your tires with nitrogen will save you money on gas, not to mention offer better performance than air. But is this true?

Read the full story here


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Comments

  • 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.
  • 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.
  • 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 [email protected]% 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.
  • bwms1bwms1 Posts: 1
    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_tankrusty_tank Posts: 1
    edited December 2014
    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.
  • steverstever Posts: 52,462
    edited January 2015
    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.
  • richardburnsI can not duplicate your findings. If an automobile gets .6% better mileage, based upon 15,000 miles and $3 gas, the savings would be just $10.75. It would cost $28 to fill all 4 tires plus the cost and hassle of procuring nitrogen. Add to the fact that with or without nitrogen, temperature changes will necessitate that tires be frequently topped. Compressed air is easy to find. Nitrogen is not. Many owners may drive longer on under-inflated tires totally negating any advantage.
  • avs007avs007 Posts: 100
    The best thing about filling with N2, is not that the molecules are bigger and you leak less air... The best thing, is that the N2 in the filling station's tank, is pure N2, which means no water vapor... Water vapor is actually what is responsible for the wide fluctuations in tire pressure with temperature.

    With that being said, I have my own air compressor at home, and I installed an in-line line dryer, which removes moisture from the air... Since I did this, I only have a couple pound variance with termperature in my tires, unlike before when I filled with gas station air... (Last time I got gas station air, if I sprayed my hand with air, my hand became covered in water....)
  • texasestexases Posts: 8,832
    If N2 is free, fine, get it, otherwise it's not worth the cost. N2 and air are IDENTICAL whey it comes to temperature effects. The web sites that promote N2 are 90% BS. Water vapor is a minor difference. Major problem- folks with N2 might wait getting their tires filled if N2 isn't available, negating all benefits.
  • thecardoc3thecardoc3 Posts: 4,995
    I fill every tire that I replace with approximately 78% pure nitrogen, no extra charge.
  • Sandman6472Sandman6472 Coral Springs, FLPosts: 4,860
    From my experiences with it, just pure nonsense!!!

    The Sandman :) B)

    2015 Audi A3 (wife) / 2015 Golf TSI (me) / 2019 Chevrolet Cruze Premier RS (daughter #1) / 2008 Hyundai Accent GLS (daughter #2)

  • Thinker5, you need to revisit your calculations. 15,000 x 0.6% = 90 x $3.00 = $270. Although the last part should now be modified to 90 x $2.00 = $180
  • Nitrogen has very real and measurable benefits for some. I was getting up to a 16 psi change driving from a cold morning in Chicago to a warm day in Dallas. If my tires were at rated pressure in Chicago they would be over the max inflation in Dallas. If I averaged it out, I would either have a harsh ride or poor mileage, depending on the temperature. I'm not fond of stopping at poorly lit gas stations outside of Memphis at 3 a.m. just to mess with my tires.

    I had nitrogen put in and the fluctuation dropped to 6 psi under the same conditions. This makes sense when you use the ideal gas law. You should only see about a 2% to 3% change in tire pressure for every 10 degrees of temperature change. The large pressure fluctuation is caused by vapor pressure from moisture inside the tire. Dry air will also fix this issue, it doesn't need to be nitrogen. Any shop with tools should have a dry air source. Just have them drain and refill your tires a couple of times with dry air if you're having problems like the ones I described above.

    Generally, cars with low profile tires designed for performance will be affected the most. Their volume doesn't change much due to the stiff construction of the tire, and the grip of the tire causes more friction and heat during operation. Most trucks, SUV's, and regular vehicles won't benefit much from dry air / nitrogen. However, don't let people tell you it's a myth. There are too many variables going on for the average idiot to understand. Just because Bubba's farm truck never had an issue doesn't mean your Mercedes won't.
  • texasestexases Posts: 8,832
    Pure nonsense. Air and nitrogen behave IDENTICALLY with respect to temperature changes. Can't change physics: PV=nRT
  • Sandman6472Sandman6472 Coral Springs, FLPosts: 4,860
    Funny how one hears such conflicting stories on this issue, never know what to do. Have tried it a few times on both vehicles but honestly, haven't seen much benefit from nitrogen to be honest. But that's just me, one sample in such a large group. I just don't know but if offered it, I will definitely chose the nitro.

    The Sandman :) B)

    2015 Audi A3 (wife) / 2015 Golf TSI (me) / 2019 Chevrolet Cruze Premier RS (daughter #1) / 2008 Hyundai Accent GLS (daughter #2)

  • texasestexases Posts: 8,832
    Trust freshman physics. Both nitrogen and oxygen are ideal gases at road temperatures and pressures. And air is 78% nitrogen - why should it act any different than nitrogen?
  • @texases Besides the obvious(because by very definition they are different -duh) I'm a girl and I can tell ya nitrogen and oxygen act different in different temperatures. (Grinning) It's not because of Freshman physics (i take it you missed that class or else you could answer your own question) that I know the answer, either. I read the article and comments above (I'm referring to the article above the text box you commented in.) -smiles
  • texasestexases Posts: 8,832
    Actually they don't. Honest. I make my living understanding these things. Anyone who says they expand differently with temperature is either sadly mistaken or lying because they sell nitrogen equipment. 
  • thecardoc3thecardoc3 Posts: 4,995
    texases said:

    Actually they don't. Honest. I make my living understanding these things. Anyone who says they expand differently with temperature is either sadly mistaken or lying because they sell nitrogen equipment.

    You should see the reactions that I get when teaching the right way to inflate tires.
    https://en.wikipedia.org/wiki/Boyle's_law
  • texasestexases Posts: 8,832

    texases said:

    Actually they don't. Honest. I make my living understanding these things. Anyone who says they expand differently with temperature is either sadly mistaken or lying because they sell nitrogen equipment.

    You should see the reactions that I get when teaching the right way to inflate tires.
    https://en.wikipedia.org/wiki/Boyle's_law
    I can only imagine. Just for grins I looked up the "Z" factor (deviation from ideal gas) for nitrogen and for air. At 100 psi it's 0.998 for nitrogen, 0.997 for air, a one tenth of one percent difference. So, OK, if someone wants to claim a 30 psi tire that increase to 33 psi with air when heated, and 0.003 psi different (3 psi X 0.001) with nitrogen, well, I wouldn't argue...
  • steverstever Posts: 52,462
    That difference goes away if you use dexos air. ;)
  • capriracercapriracer Somewhere in the USPosts: 877
    A couple of comments:

    First, not only is there an Ideal Gas Law, there is also the Law of Partial Pressure of Gases - which states that you can treat a mixture of gases as though they were not mixed. So the pressure at sea level for oxygen in air is 3.1 psi (14.7 X 21% = 3.1) AND if you fill a tire with 100% N2, that 3.1 psi O2 will be trying leak back INTO the tire. This has been demonstrated to occur. So you can not keep a 100% N2 mixture in a tire.

    Second, water vapor behaves like a gas (which is what it is), so unless there is liquid water in the tire, the inflation pressure follows the Ideal Gas Law.

    Further, water vapor can diffuse through the tire just like N2 and O2 do, so eventually there will be no water in the tire. As proof, I offer that when tires are removed from service, you don't find puddles of water inside, even though they may have used liquid mounting lube when mounted.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    You might also hear the pitch about 02 molecules being smaller than nitrogen molecules (true), and thus they can "escape" more easily through the porosity of the tire. However, like most "bad science", what sounds plausible really isn't, because the different in size is only 3%.
  • thecardoc3thecardoc3 Posts: 4,995

    You might also hear the pitch about 02 molecules being smaller than nitrogen molecules (true), and thus they can "escape" more easily through the porosity of the tire. However, like most "bad science", what sounds plausible really isn't, because the different in size is only 3%.

    http://www.getnitrogen.org/pdf/graham.pdf

  • Sandman6472Sandman6472 Coral Springs, FLPosts: 4,860
    O K folks, so bottom line...is it worth it or not? Have tried it and didn't find a difference...at all. Seems like nonsense to me, just a way to make a buck on folks. Anyways, hasn't regular air been o k for years now???
    My money's on that it doesn't make any difference at all.

    The Sandman :) B)

    2015 Audi A3 (wife) / 2015 Golf TSI (me) / 2019 Chevrolet Cruze Premier RS (daughter #1) / 2008 Hyundai Accent GLS (daughter #2)

  • kyfdxkyfdx Posts: 120,532

    O K folks, so bottom line...is it worth it or not? Have tried it and didn't find a difference...at all. Seems like nonsense to me, just a way to make a buck on folks. Anyways, hasn't regular air been o k for years now???
    My money's on that it doesn't make any difference at all.

    The Sandman :) B)

    I wouldn't pay extra for it, but it can't hurt anything.

    No one around here charges extra for it.

    Did you get a good deal? Be sure to come back and share!

    Edmunds Moderator

  • Sandman6472Sandman6472 Coral Springs, FLPosts: 4,860
    Personally, I wouldn't pay for it either.

    The Sandman :) B)

    2015 Audi A3 (wife) / 2015 Golf TSI (me) / 2019 Chevrolet Cruze Premier RS (daughter #1) / 2008 Hyundai Accent GLS (daughter #2)

  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,490
    I'd take it for free.
  • thecardoc3thecardoc3 Posts: 4,995
    I've said it before, I fill every tire with approximately 78% pure nitrogen. N/C.
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