Nitrogen Tires

[David Ragan]

What the deal with Nitrogen tires on wifes new Honda Pilot?

Less oxidation to the innerds of the tire?

How do you air up if needed?

Necessary for on-board pressure detection?

[Kent A Bathurst]

supposed to not expand/contract as much with temp changes, hence less overall issues with refilling/topping off.

tires stores have the nitro.

[Gordon Eyre]

I have been using it for years and rarely have to top off. Most tire store like Big O, etc. will have nitrogen. You usually have green valve caps on and tire stores recognize this as being pressured with nitrogen.

[Mike Lassiter]

another reason is nitrogen molecule is suppose to be slightly bigger than "air" molecule and cannot seep out as easily. I'm not sure I can agree with that (based on opinion only) in a class over the years someone stated that tires are porous. There is space between the rubber molecules that air can seep through. It's sounds feasible (I guess) but I have never researched it to see it that is accurate and factual or someone's opinion. With "air" also containing nitrogen but not 100% not sure myself what I believe.
I know if nitrogen is put in tires they are suppose to have a green colored valve stem cap to indicate it. I have had to add to low tires in the cold weather using a 12 volt pump, and just don't get concerned about it. I don't think it is anything to get anal about causing a problem. Running too low pressure in the tire is more cause for concern to me than if I put air in with the nitrogen.

[Dave Richards]

For years I've been using a mixture of gasses with nitrogen making up about 78% of the mixture. It seems to work fine in my tires.

FWIW, there's no such thing as an "air molecule." Normal clean air is comprised mostly of nitrogen molecules, oxygen molecules and trace amounts of some other gasses.

[Ken Fitzgerald]

For years I've been using a mixture of gasses with nitrogen making up about 78% of the mixture. It seems to work fine in my tires.

FWIW, there's no such thing as an "air molecule." Normal clean air is comprised mostly of nitrogen molecules, oxygen molecules and trace amounts of some other gasses.

Those biomedical engineers are brutal!

[Dave Richards]

Those biomedical engineers are brutal!

Especially when gas is the main focus.

[David Ragan]

For years I've been using a mixture or gasses with nitrogen making up about 78% of the mixture. It seems to work fine in my tires.

FWIW, there's no such thing as an "air molecule." Normal clean air is comprised mostly of nitrogen molecules, oxygen molecules and trace amounts of some other gasses.

I thought it was more like 80%

I thought that it was to protect the rubber from oxidation. Not true?

Those biomedical engineers are brutal!

Yep. It is all about the Science, though, aint it?

[Jerome Stanek]

It's a gimick to get you to pay more for air. If the oxygen escapes and you top it off you will keep putting in more nitrogen. When they first air a tire there is oxygen in it.

[Phil Thien]

Didn't we just have a similar thread in the last year?

I think the consensus was that repeated topping-off with atmosphere would result in oxygen leaking out and nitrogen staying in, so using a regular air compressor is the equiv. of using nitrogen, over time.

[John Stankus]

another reason is nitrogen molecule is suppose to be slightly bigger than "air" molecule and cannot seep out as easily. I'm not sure I can agree with that (based on opinion only) in a class over the years someone stated that tires are porous. There is space between the rubber molecules that air can seep through. It's sounds feasible (I guess) but I have never researched it to see it that is accurate and factual or someone's opinion..

There are a lot of misunderstandings when it comes to tires and inflation.

From a physical chemist's viewpoint (my day job is chemistry professor)

Dry Air is made up of 78% nitrogen 21%oxygen 1% Argon and other stuff

The real issue for pressure change is if there is a lot of moisture in the tire, enough that some can be liquid at lower temperatures. This will cause pressure changes as the liquid vaporizes as the temperature increases. But this pressure rise should be proportional to the vapor pressure of water, which means that it could be at about 4 psi for a tire temperature of 150 F.

There is a pressure change due to temperature difference from 70F to 150F should be a 15% increase in pressure.

The property of a gas passing through something like a tire wall is called effusion. The rate of effusion is proportional to the inverse of square root of the molecular weight of the gas. Nitrogen molecules and oxygen molecules are about the same size but oxygen is a heavier molecule(32 grams/mole vs 28 grams/mole for nitrogen) Nitrogen should effuse about 7% faster than oxygen, but I would venture to argue the rates are so low that this difference is not a practical concern. There are questions of the nitrogen and oxygen solubility in the tire rubber, but again I think the rate is so low to be of little consequence. My guess would be the loss of pressure in tires is more likely from seepage around the bead on the rim and the valve than effusion through the sidewall of the tire.

One of the last times the nitrogen in tires thing came up, I did a calculation as to how much oxygen was available to react and it was pretty small amount. Real rough back of the envelope indicated that if all the oxygen reacted with the rubber it would be about 90 milligrams of rubber that would be reacted, or about 0.0008% of the tire mass. Again I would think this is negligible.

I would say dry air should be just fine. From my autocross racing days the pressure growth due to liquid in the tire was a concern for some, but they were running slicks that may have been running at the 20 psi range.

Personally, I think the nitrogen in tires is for two reasons 1) marketing and 2) to provide more profit for the tire stores.

In high speed aircraft tires, nitrogen is specified not for leakage concerns but to reduce chance of fire during catastrophic tire failure.

John


p.s. As a related aside, most people don't realize that humid air is LESS dense than dry air. This is due to the water molecule having a much lower mass than oxygen or nitrogen molecules.

[Chris Padilla]

air-composition-pie-chart2.jpg

There ya go.

[Chris Padilla]

p.s. As a related aside, most people don't realize that humid air is LESS dense than dry air. This is due to the water molecule having a much lower mass than oxygen or nitrogen molecules.

Just to be a bit more rigorous, nitrogen and oxygen are usually bound together with another nitrogen and oxygen hence why we often see N2 and O2 written. The bond is quite strong as I understand it. So if the amount of water vapor increases, water being H2O of course, I can see that: O2 and N2 are heavier than H2O.

[Steve Peterson]

For years I've been using a mixture or gasses with nitrogen making up about 78% of the mixture. It seems to work fine in my tires.

That's what I use to top off also. All the stations around here fill up with nitrogen. It is perfectly OK to top off with a 78% nitrogen, 21% oxygen, 1% argon mixture.

Half of the reasons listed on their flyer are completely against the laws of physics. A properly inflated nitrogen tire will have exactly the same gas mileage and performance as a properly inflated "air" tire. All gasses experience the same amount of pressure change relative to temperature. The only true statement is that nitrogen filled tires loose pressure slower than an air filled tire, but the effects are very minor.

Steve

[Art Mann]

supposed to not expand/contract as much with temp changes, hence less overall issues with refilling/topping off.

tires stores have the nitro.

That claim is utterly false. Anyone who has completed a high school chemistry class and remembers anything about it will know that. Nitrogen, oxygen, carbon dioxide, water vapor and the trace gasses that make up what we call air all obey closely the predictions of the ideal gas law. The formula is PV=nRT, where P is pressure, V is volume, T is temperature and n and R are both constant numbers. What it says is that as temperature rises, either pressure, volume or both increase. Since the volume of a tire is pretty much fixed, the pressure goes up with the temperature, no matter what gas you are talking about. It doesn't matter whether the gasses are pure or mixed. The only time when this formula starts to fail is when the gas in question is so compressed that it becomes a liquid. The only reason why anyone who really understands what is going on would prefer pure N2 is that it is normally sold anhydrous.