Monday, February 05, 2007

Nitrogen for tires?

Now I am not a physicist or chemist but this article, "Nitrogen for Tires just hot air?" by Dave Toplikar in Sunday's Lawrence Journal World caught my attention. Apparently tire places are hawking nitrogen for tires rather than regular compressed air. One of Lawrence's tire places has recently installed equipment for filling tires with nitrogen at $5.00 a pop claiming that nitrogen filled tires hold their pressure three times longer than when filled with regular air. Tires filled with nitrogen also supposedly run cooler in the summer and since nitrogen is relatively inert, less corrosive to the innards of a tire than regular air.

Toplikar was rightfully skeptical of these claims because, recalling one of those facts that one should have learned if one was paying attention in school, or else watched the Discovery Channel, namely that "air" is about 78% nitrogen gas 21% oxygen gas with the balance being argon, water vapor, carbon dioxide methane and various other gasses. Since of the advantage of nitrogen supposedly rests with it being a bigger molecule, Toplikar asked the chair of KU's chemistry department about this and the chair gave an apt description of the relative sizes of a nitrogen molecule namely the difference is like a Chipotle burrito with lettuce vs one without lettuce. If there is any advantage to using pure nitrogen then is ought to rest with the reduction in corrosiveness but the chair was skeptical of that.

Molecular size is a bit tricky. As a quick comparison, we can use the covalent radius defined as 1/2 the distance between to identical covalently bonding nuclei. This is measured in picometers (1 pm= 1x 10-12 m). Nitrogen's covalent radius is 73pm so the length of a nitrogen molecule ought to be 4 X 75pm or 300 pm. A molecule of oxygen ought to be just a shade smaller 4 X 73pm or 292pm. So an oxygen molecule ought to be a little less than 3% smaller than a nitrogen molecule.

The companies that process nitrogen and make equipment for doing this tire filling are all for using nitrogen and there is even a Get Nitrogen Institute to promote nitrogen use including in tires. This site has a little link to "Deep Science" so let's see what is there. First is a "gas permeability table" ( Now this gets the geek juices flowing. But the table makes absolutely no sense. It is basically a ranking of permeabilities with no units and no explanation of how the data were collected. Nitrogen gas and methane are both shown as having equally slow permeabilities and water vapor the worse, but beyond that there is no way to assess what these rankings mean. How much more rapid is the permeability of water vapor than nitrogen gas?

This "table" is typical of how promotional literature often times uses misleading graphics. Here is another promotion ( showing a huge apparent size difference between oxygen and nitrogen atoms when the real difference is a lot smaller.

Fortunately the site does provide some quantitative looking reports, for instance part of a thesis ( on the use of nitrogen in tires suggesting from theoretical considerations that the permeability differences between nitrogen gas and oxygen that tires inflated with nitrogen gas should lose pressure at half the speed that tires filled with regular air.

So it's back to the web to look for articles relating molecular size to permeability through various sorts of films and found some interesting tidbits. For example at Stanford, scientists are attempting to use membrane separation to extract carbon dioxide based solely on molecular diameter which is the main determinant of diffusion if the pores in the membrane are at the nano scale, in line with the molecular sizes. (

The idea is to use these membranes as a sieve to sort out the carbon dioxide produced by fossil fuels and the sequester it. There is a nice picture illustrating the concept. This suggests the tire rubber must have a complex of pores in the molecular size range of oxygen or smaller. Further it's likely that the nanoscale structure of these pores is makes the effect more like a series of sieves analogous to the sort of cascade of gas centrifuges used to sort out different isotopes of uranium by small differences in mass. So it is possible that small differences in molecular size lead to differences in permeabilities of a tire.

Getting back to tires, there apparently is benefit for freight truck tire longevity as described in this article ( This article notes that a truck tire properly inflated might loose 2 pounds per square inch in three months as opposed to 2 pounds per square inch per month. But these are big semi tires. For space shuttle and other sorts of high performance tires maybe using nitrogen gas makes sense. These tires operate at much greater extreme of temperature and pressure than passenger car tires.

The car talk guys...and that's where I get my limited knowledge about cars have this to say about racing tires and nitrogen:

"One (i.e., Indy 500) racers use nitrogen in their tires because when you're traveling around an oval track at 200 mph, you want your tire pressure to be entirely predictable. They even "stagger" the tire pressure on those cars, making the outside tires a little fuller than the inside tires to keep the car turning inward. And at those speeds, an eighth of an inch in tire height can make a huge difference."


I suspect the predictability the car guys are referring to arises from the fact that regular air has water vapor in it so when the wheels cool, some of that vapor changes phase making the change in tire volume less regular.

Some of the advantage of nitrogen is also allegedly due to the fact that it is relatively inert compared to oxygen and one exhibit ( at the Get Nitrogen's "deep science" link attempts to address this. The study authors found that using nitrogen gas does indeed reduce the aging of tires and this seemed most pronounced for peel strength, the force required to separate the belts in the radial tires tested. But these tires were not run on passenger cars but 'cooked' for up to 12 weeks at 60 degrees centigrade. Indeed the study's authors note:

"Nonetheless, it is perhaps a fair assumption to say that there would be some improvement in tire durability if nitrogen was used as the inflation media, but it is too soon to speculate as to how much of an improvement it would be."

But does using nitrogen vs air in car tires make any difference for us as consumers? Probably not at $5.00 per tire when just periodic checking of pressure is sufficient, assuming of course we happen to have two quarters on us when we think about it to pay for the air. But this whole controversy illustrates how organizations can exploit a partial truth and through a little sleigh of hand can produce a new perceived need for the consumer.

By the way, in my searches I encountered a fascinating 19th century scientist who is not well known to non chemists, namely Josef Loschmidt who was the first scientist to estimate the size of molecules using the kinetic theory of gasses. There is a wonderful scientific biography for Loschmidt in Physics Today March 2001 which is online at

Balder, Afred and Leonard Parker (2001) Joseph Loschmidt, Physicist and Chemist. Physics Today Vol 54(3) p 45.

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Anonymous said...


I found some useful independent additions regarding the Nitrogen in Tyres issue, in the diffusion cases stories section at:

Here, there is also a discussion on this subject, see the following threads:


Anonymous said...

Great post, thanks for compiling this information!

Anonymous said...

There is an old saying - "those that can do -do and those who can't do teach". The real world is that nitrogen and the physical properties of nitrogen in improving the perfomance of tires is well documented by the tire manufacturers. But the real savings here is that most people simply do not routinely check their tire pressures (about 85% of us are driving on underinflated tires according to a DOT study) and nitrogen would be a safety benefit to a majority of the population. But the fuel savings is real and psuedo scientist like you help prevent the conversion to nitrogen which could save our country hundreds of millions of dollars a year and be a part of reducing our nations dependency on foreign oil.

Paul D. said...

Gee Norman,

You must be really touchy if all you can do is slam someone you don't even know. Not only that...resorting to old sayings rather than logic. hmmmm.

I agree with you about under inflated tires. But if you think nitrogen is such a great thing for the average driver such as me the data!

Anonymous said...

Some changes with regard to my first post (see above):

Check the following sources for Nitrogen in tyres:

plastics discussion forum

Nitrogen diffusion through tyre materials


Anonymous said...
This comment has been removed by a blog administrator.
tyre changers said...

I learn a lot from this article.I read other writings about nitrogen for tires but i can't find the specific advantage than using a normal air until i figure out here.Thanks for the useful input.

Anonymous said...

I think Pure Nitrogen has benefits over Compressed air because of the Water vapor which can settle on the insides of tires, possibly corroding them from the inside. Humid Air has different composition than dry air.

wheel alignment equipment said...

With nitrogen tire inflation,improvements can be noted in a vehicle's handling,fuel efficiency and tire life through better tire pressure retention,improved fuel economy and cooler tire temperatures.

wheel balancing machine said...

I've been too curious about this issue.Nitrogen in tires is becoming a popular replacement for standard air.With nitrogen tire inflation,improvements can be noted in a vehicle's handling,fuel efficiency and tire life through better tire pressure retention,improved fuel economy and cooler running tire temperatures.

Tyre Changer said...

Nitrogen became so popular due to many advantages it has for tires.Nitrogen improves handling and road holding.It reduce rolling resistance which improves miles per gallon.

Enjoy Gas said...

Coke or Pepsi, bottled water or tap, generic or name brand? The questions over the trivial remain.

In the crash of an aircraft or race car, perhaps limiting the sudden release of more oxygen from an exploding tire may have some safety implications. For the rest of the world, just check your pressure more frequently especially as the seasons change.

With each oil change, have tires rotated and set the their pressures to factory recomended levels. Then you can save your money for a Pepsi or bottle of water while you wait ... no joke, you may need two, :-).

tyres in Redditch said...

Wow.. this is great! I can say that Nitrogen tires will also run cooler then tires inflated with air, which keeps tire pressures more constant.

stainless coil said...

It's getting more interesting to learn nitrogen components and how it's becoming an advantage to modern cars.Nitrogen makes your tires achieve much cooler running temperatures.Other advantages were stated but also keep in mind to make sure your tires were properly inflated,either by nitrogen or ordinary air.

Double Glazing said...

Nitrogen on tires discovery makes a lot of difference on auto industry.When the handling and performance improve,it means longer tyre life.Thus,saving money for each customer in changing their tyres.

garage equipment said...

Yes,a hot topic especially last year.I read reviews and analysis from different articles talking about the positive and negative impact of nitrogen on tyres.Some says it leaks from tires at a slower rate than air, so tires stay inflated longer at full capacity, which helps a vehicle attain maximum fuel efficiency.

Anonymous said...

Nitrogen works far better than AIR because of identical property of gas

Redditch tyres said...

I became interested with this topic since i first read an article talking about its advantages.It's a great addition to save fuel and money nowadays.Whereas,tires is one main part to help your car run good.

unite tyre changing machine said...

Nitrogen is compact where it doesn't escape on tires more often.It provides longer tire life that saves your money from buying a new one.

tyre machines said...

Nitrogen leaks less than air on your tires.This makes it more compact and gives longer tire life.It will turn out to improve gas milegae.

party bags said...

Great read! I figured out the specific advantage of using normal air for tires. You explained it in the easiest way.

jay said...

After reading both articles and the Consumer Reports study, I am convinced that there is a small benefit to nitrogen. I wouldn't pay $5 for a fill, but since I buy my tires at Costco, and they don't charge for nitrogen, it's kind of a win-win situation. Now if I would just remember to check my tire pressure, and maybe drive more consistently.

Anonymous said...

I thought the whole reason for filling tires with nitrogen was to reduce or eliminate corrosion in the TPMS parts.