Nitrogen in tires

[CamarilloBrillo]

Thank you for correcting the misinformation. I think what I meant to say is that when moisture is combined with air (which contains oxygen) it is much more corrosive and can cause more oxidation that moisture combined with 100% nitrogen. If this is still not correct, please let me know.

It would be my understanding that iron, for example, would not rust in the presence of pure nitrogen and water - I believe this to be true. I doubt that any of this is pertinent to the inside of a tire as I doubt oxidation is a leading problem with tires over time unless it's long term storage.

I have nitrogen in my tires because the dealer put it there and I intend to keep it there but I seriously doubt that it will help preserve my tires for any length of time with the possible exception of better maintaining pressure.

 

[Mark_888]

It would be my understanding that iron, for example, would not rust in the presence of pure nitrogen and water - I believe this to be true. I doubt that any of this is pertinent to the inside of a tire as I doubt oxidation is a leading problem with tires over time unless it's long term storage.

I have nitrogen in my tires because the dealer put it there and I intend to keep it there but I seriously doubt that it will help preserve my tires for any length of time with the possible exception of better maintaining pressure.

I agree and mentioned that Genesis owners have aluminum alloy wheels which are not made of iron.

My replacement tires also came installed with Nitrogen for free (at Costco), and I refill them with air when needed. I have noticed that they "seem" to hold tire pressure better with 100% Nitrogen (or near 100%) than air, but that is not a scientific observation since the tires are different than the OEMs.

 

[UmALum1990]

If you need to add more "pressure"to your tires, you can add regular air. However, nitrogen filled tires do not lose pressure as quickly as regular air filled tires. I have used nitrogen in my tires for the last 5 years on different vehilcles, and have gone service to service without having to adjsut pressure. Also, the ride is better, tire life is improved, and there is less pressure fluctuation in low to high temperatures. If you prefer to have nitrogen in your tires rather than adding air for an adjustment, you will still have to go to your dealer.

 

[Philth]

Nitrogen does not expand with heat or contract with cold. The MPG gain is from the tires not changing in pressure.

 

[Mark_888]

Nitrogen does not expand with heat or contract with cold. The MPG gain is from the tires not changing in pressure.

Are you sure about that? If so, you should publish an article in a scientific journal for that discovery, as I am sure you will win the Nobel Prize in Chemistry for it.

 

[CamarilloBrillo]

Are you sure about that? If so, you should publish an article in a scientific journal for that discovery, as I am sure you will win the Nobel Prize in Chemistry for it.

I was going to post this when I got home:

Nitrogen Compressibility Factor (Z) (1.013 bar and 15 °C (59 °F)) : 0.9997
Oxygen Compressibility Factor (Z) (1.013 bar and 15 °C (59 °F)) : 0.9994
Air Compressibility Factor (Z) (1.013 bar and 15 °C (59 °F)) : 0.9992

Bottom line is that nitrogen/oxygen/air are all the same for all practical purposes - well, tires at least.

 

[Mark_888]

I was going to post this when I got home:

Nitrogen Compressibility Factor (Z) (1.013 bar and 15 °C (59 °F)) : 0.9997
Oxygen Compressibility Factor (Z) (1.013 bar and 15 °C (59 °F)) : 0.9994
Air Compressibility Factor (Z) (1.013 bar and 15 °C (59 °F)) : 0.9992

Bottom line is that nitrogen/oxygen/air are all the same for all practical purposes - well, tires at least.

Even if nitrogen and air behaved noticeably different, to say that nitrogen does not change in pressure at all when temperature changes, is obviously not true. At normal temps, the relationship between temperature and pressure is fairly linear, for both air and nitrogen.

The part that gets tricky is when water is introduced into the equation (more likely with compressed air), but I doubt there is enough water in most tires to make a noticeable difference.

 

[CamarilloBrillo]

Even if nitrogen and air behaved noticeably different, to say that nitrogen does not change in pressure at all when temperature changes, is obviously not true. At normal temps, the relationship between temperature and pressure is fairly linear, for both air and nitrogen.

The part that gets tricky is when water is introduced into the equation (more likely with compressed air), but I doubt there is enough water in most tires to make a noticeable difference.

I'm pretty sure we are in agreement.

 

[Philth]

Whew, you got me there. I should have elaborated more about expanding less than air, and not at all.

For your reading pleasure:
http://www.popularmechanics.com/cars/how-to/repair-questions/4302788


I work aircraft maintenance and nitrogen has many advantages for aircraft tire use. One of those is that the tires heat up substantially when landing. They also cool down substantially when at cruise altitude (around -35C). The pressure doesn't swing all that much between the two scenarios. How can this be? Maybe I should go write that paper...

 

[STREETS]

Or we can use solid rubber tires or those Michelin Tweels and forget about air/ nitrogen altogether!

http://static.ddmcdn.com/gif/tweel-airless-tire-2.jpg

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[Mark_888]

Whew, you got me there. I should have elaborated more about expanding less than air, and not at all.

For your reading pleasure:
http://www.popularmechanics.com/cars/how-to/repair-questions/4302788

I work aircraft maintenance and nitrogen has many advantages for aircraft tire use. One of those is that the tires heat up substantially when landing. They also cool down substantially when at cruise altitude (around -35C). The pressure doesn't swing all that much between the two scenarios. How can this be? Maybe I should go write that paper...

I read somewhere that the FAA requires nitrogen in tires in order to prevent ice buildup as result of the typical amount of moisture in an aircraft tire filled with air. As you know, temps get very cold at cruising altitudes of aircraft. But I have no personal knowledge of this, and that is just what I read.

As to the pressure difference when a gas is heated or cooled, it definitely happens. Not sure why it doesn't happen as much with nitrogen filled tires, or if there is some other explanation. It may be that it is related to less moisture in a nitrogen tire, and less heat transfered from the tread to the gas inside the tire, rather than actual differences in the temp of the gas (perhaps the moisture transfers heat faster inside the tire than would otherwise be the case). There seems to be a lot of stuff on this subject on the Internet and it is hard to tell what is accurate vs folklore.

Some of the stuff, like nitrogen getting better MPG is definitely due to the fact that nitrogen filled tires are less likely to be under-inflated than air filled tires, but that fact often gets lost in translation and people think that the nitrogen itself gets better MPG than air even when both are at the same pressure (it doesn't).

The link you provided is not conclusive. Race cars and aircraft put extreme demands on tires that are not typical of the average automobile. When a race car or plane is traveling on pavement at 150 - 200 MPH, even a slight difference in pressure (the link mentions 1/2 PSI difference) makes a big difference in tire performance and handling predictability.

This link talks about aircraft tires and nitrogen, but says nothing about pressure changes:

Commercial Airlines – The Federal Aviation Administration (FAA) requires nitrogen in all commercial aircraft tires to eliminate the potential for water vapor (inherent in normal compressed air) from freezing at high altitudes.
http://getnitrogen.org/why/​

 

[Mark_888]

Here is an interesting quote about aircraft tires and pressure difference with nitrogen.

Aircraft tires are usually inflated with nitrogen or helium in order to minimize expansion and contraction from extreme changes in ambient temperature and pressure experienced during flight. Dry nitrogen expands at the same rate as other dry atmospheric gases, but common compressed air sources may contain moisture, which increases the expansion rate with temperature. Aircraft tires generally operate at high pressures, up to 200 pounds per square inch (14 bar; 1,400 kPa) for airliners, and even higher for business jets.
http://en.wikipedia.org/wiki/Tire​

It appears that this confirms what I previously said, that the moisture in typical air filled tires is what causes the more rapid increases in air pressure when heated, rather than the inate difference between and air and nitrogen.

 

[CamarilloBrillo]

Here is an interesting quote about aircraft tires and pressure difference with nitrogen.

Aircraft tires are usually inflated with nitrogen or helium in order to minimize expansion and contraction from extreme changes in ambient temperature and pressure experienced during flight. Dry nitrogen expands at the same rate as other dry atmospheric gases, but common compressed air sources may contain moisture, which increases the expansion rate with temperature. Aircraft tires generally operate at high pressures, up to 200 pounds per square inch (14 bar; 1,400 kPa) for airliners, and even higher for business jets.
http://en.wikipedia.org/wiki/Tire​

It appears that this confirms what I previously said, that the moisture in typical air filled tires is what causes the more rapid increases in air pressure when heated, rather than the inate difference between and air and nitrogen.

In aircraft temperatures and pressures which is not necessarily analogous to automobile temperatures and pressures.

 

[Philth]

Here is an interesting quote about aircraft tires and pressure difference with nitrogen.

Aircraft tires are usually inflated with nitrogen or helium in order to minimize expansion and contraction from extreme changes in ambient temperature and pressure experienced during flight. Dry nitrogen expands at the same rate as other dry atmospheric gases, but common compressed air sources may contain moisture, which increases the expansion rate with temperature. Aircraft tires generally operate at high pressures, up to 200 pounds per square inch (14 bar; 1,400 kPa) for airliners, and even higher for business jets.
http://en.wikipedia.org/wiki/Tire​

It appears that this confirms what I previously said, that the moisture in typical air filled tires is what causes the more rapid increases in air pressure when heated, rather than the inate difference between and air and nitrogen.

I agree. Compressed air = moisture in air. Nitrogen = no moisture. I'm not too sure compressed air can even have no moisture in it, or we would be using it on aircraft long ago.

So back to the end result of air in vehicle tires. I regularly have seen around a 5-10 psi shift from hot to cold climates in my tires, and vice versa. I believe it is because compressed air is used to inflate them, whether its moisture inside the compressed air or not.

 

[CamarilloBrillo]

I work aircraft maintenance and nitrogen has many advantages for aircraft tire use. One of those is that the tires heat up substantially when landing. They also cool down substantially when at cruise altitude (around -35C). The pressure doesn't swing all that much between the two scenarios. How can this be? Maybe I should go write that paper...

I have a question ... is it a normal maintenance procedure to regularly test the nitrogen level in the tires? I ask because I have read, as a response to this thread, that after around 3 months the oxygen level in a nitrogen filled tire can come back to near normal atmospheric levels. This seems counter-intuitive but I know permeation can happen from lower to higher pressure situations.

Since water seems to be the real culprit I suspect that the nitrogen level wouldn't be all that important but was just curious.

 

[Mark_888]

I have a question ... is it a normal maintenance procedure to regularly test the nitrogen level in the tires? I ask because I have read, as a response to this thread, that after around 3 months the oxygen level in a nitrogen filled tire can come back to near normal atmospheric levels. This seems counter-intuitive but I know permeation can happen from lower to higher pressure situations.

Since water seems to be the real culprit I suspect that the nitrogen level wouldn't be all that important but was just curious.

I have read that permeation does occur, but they were not clear about the rate of permeation. I have also heard that once you get to 96%+ nitrogen, that is as about as high as one can get without rapid permeation back to that value.

However, I just got my tires rotated today at Costco (no charge), and the receipt says they refilled them with nitrogen, so maybe permeation is a bigger issue than I thought.

 

[CamarilloBrillo]

I have read that permeation does occur, but they were not clear about the rate of permeation. I have also heard that once you get to 96%+ nitrogen, that is as about as high as one can get without rapid permeation back to that value.

However, I just got my tires rotated today at Costco (no charge), and the receipt says they refilled them with nitrogen, so maybe permeation is a bigger issue than I thought.

I have a mechanic that I like that maintains my Toyota and he put nitrogen in the tires I bought from him around a year ago. I called him to ask if he had a nitrogen analyzer and he said that he had just borrowed one this week because they were expensive to test his nitrogen source - apparently he buys compressed nitrogen and doesn't have a separator. He was shocked when I suggested that oxygen could permeate back into the tires because it was under pressure. I told him that it difficult to understand but it could happen and he agreed to test the tire content to see the concentration. It will be interesting to see.

 

[Philth]

I have a question ... is it a normal maintenance procedure to regularly test the nitrogen level in the tires? I ask because I have read, as a response to this thread, that after around 3 months the oxygen level in a nitrogen filled tire can come back to near normal atmospheric levels. This seems counter-intuitive but I know permeation can happen from lower to higher pressure situations.

Since water seems to be the real culprit I suspect that the nitrogen level wouldn't be all that important but was just curious.

We check pressures, but don't check for oxygen levels. We service the struts with n2 as well. We change the strut pressures corresponding with aircraft gross weight.

 

[Mark_888]

We check pressures, but don't check for oxygen levels. We service the struts with n2 as well. We change the strut pressures corresponding with aircraft gross weight.

How do you know what the pressure of the tires are at cruising altitude (significantly colder than at landing altitude).

 

[Philth]

How do you know what the pressure of the tires are at cruising altitude (significantly colder than at landing altitude).

We don't know; I'm sure the engineers do. However, I can't see the tires warming up completely to the ambient temp at landing. Then, after landing, the brakes heat up the tires quite a bit. What most would consider a pretty big shift in temperature.