[kdlynn (OP)]

I have heard a lot lately about filling your car tyres with nitrogen, and i was wondering if anyone knows how this makes a difference in gas mileage. also, are there any risks?

[another_someone]

Cannot see that this would make the least difference - air is 80% nitrogen anyway.  If you have something in the wheel that is susceptible to oxidation, then you might want to remove the oxygen, leaving about 99% nitrogen - but I cannot see that as an issue, and using natural air is a lot lot cheaper (even though nitrogen is cheep, but air is free).

[kdlynn (OP)]

hmmm... i wonder why they are trying to say that this improves your gas mileage. probably to make money. they advertised it at $30

[Cut Chemist]

This is from:

http://ezinearticles.com/?Selling-Nitrogen-In-Tires---Is-It-All-A-Lot-Of-Hot-Air?&id=38142


The earths atmosphere is composed primarily of Nitrogen (78%), the remaining balance is a mixture of Oxygen (21%) and a small percentage of Ozone, Argon and Carbon gases. Isn’t it ironic that the very gas (oxygen) that sustains life also causes organic materials to decompose and metals to rust?

Remove The Oxygen And Stop The Rot

To stop this decomposition you simply need to remove the oxygen from the ‘air’. (Incidentally, removing oxygen also means that you remove water because water is two parts Hydrogen gas, and one part Oxygen gas.)

Removing Oxygen from products is not new, we do it all the time with our food and drink. In fact, if we did not remove the oxygen our food would not likely last long enough to make it into the hands of the consumers – or it would taste stale and unappealing.

Nitrogen In Tires

Here are a few other benefits of using Nitrogen in tires:

[1] Nitrogen is denser than Oxygen: This means the larger molecules escape less easily from tires resulting in a more gradual loss of pressure over time. According to the Michelin Tire Manual, a tire that is inflated with Nitrogen loses its pressure 3 times slower than if it were inflated with air.

[2] Nitrogen is moisture free: Pure Nitrogen inflated tires experience less steel belt and rubber degradation. Nitrogen use also reduces valve and wheel corrosion.

[3] Nitrogen provides longer tire life: Nitrogen inflated tire run cooler and require less maintenance according to the Goodyear application bulletin.

[4] Nitrogen is non-flammable: Nitrogen technology has been used in aircraft, military and race car technology for over thirty years.


In this article they quote tire companies, so who knows if their information is valid.  It makes sense that it would cause less corrosion by removing the oxygen, and that they stay inflated longer.  However, they don't mention that it gives you better gas mileage.

I think that might have been false advertising ...  What about trying Helium??

(No oxygen, Nonflammable, and Lighter than Air) 

[another_someone]

I am not aware of many people having had problems with wheel corrosion within the tyre.

That the aircraft industry might want to remove moisture from tyres, that is conceivable, given the high altitude and low temperatures they fly in - not a problem for the average motors car.  Otherwise, I can see reasons why nitrogen might be used in aircraft or racing cars in the fuel tanks to stop explosions, but not in the tyres.

I am also rather dubious that oxygen has much influence on the aging of rubber - thermal cycling is likely to have a greater influence on that.

Then again, snake oil sells well too.

[lightarrow]

This is from:
http://ezinearticles.com/?Selling-Nitrogen-In-Tires---Is-It-All-A-Lot-Of-Hot-Air?&id=38142
The earths atmosphere is composed primarily of Nitrogen (78%), the remaining balance is a mixture of Oxygen (21%) and a small percentage of Ozone, Argon and Carbon gases. Isn’t it ironic that the very gas (oxygen) that sustains life also causes organic materials to decompose and metals to rust?
Remove The Oxygen And Stop The Rot
To stop this decomposition you simply need to remove the oxygen from the ‘air’. (Incidentally, removing oxygen also means that you remove water because water is two parts Hydrogen gas, and one part Oxygen gas.)
Removing Oxygen from products is not new, we do it all the time with our food and drink. In fact, if we did not remove the oxygen our food would not likely last long enough to make it into the hands of the consumers – or it would taste stale and unappealing.
Nitrogen In Tires
Here are a few other benefits of using Nitrogen in tires:
[1] Nitrogen is denser than Oxygen

No, it's lighter: N₂ molar mass = 28; O₂ molar mass = 32.

This means the larger molecules escape less easily from tires resulting in a more gradual loss of pressure over time. According to the Michelin Tire Manual, a tire that is inflated with Nitrogen loses its pressure 3 times slower than if it were inflated with air.
[2] Nitrogen is moisture free: Pure Nitrogen inflated tires experience less steel belt and rubber degradation. Nitrogen use also reduces valve and wheel corrosion.
[3] Nitrogen provides longer tire life: Nitrogen inflated tire run cooler and require less maintenance according to the Goodyear application bulletin.
[4] Nitrogen is non-flammable: Nitrogen technology has been used in aircraft, military and race car technology for over thirty years.[/color]
In this article they quote tire companies, so who knows if their information is valid.  It makes sense that it would cause less corrosion by removing the oxygen, and that they stay inflated longer.  However, they don't mention that it gives you better gas mileage.
I think that might have been false advertising ...  What about trying Helium??
(No oxygen, Nonflammable, and Lighter than Air)

It would be a better idea, if it wouldn't diffuse through the tire, reducing pressure. I don't know how much, however.
Also, see this:
http://en.wikipedia.org/wiki/Nitrogen:

Modern applications
...
Filling automotive and aircraft tires[1] due to its inertness and lack of moisture or oxidative qualities, as opposed to air, though this is not necessary for consumer automobiles.[2][3]

I assume it could be useful for races only, where tires undo very high friction and strains.

[Cut Chemist]

No, it's lighter: N2 molar mass = 28; O2 molar mass = 32.

You're right
density of Nitrogen = 1.25 g/L
deinsty of Oxygen   = 1.43 g/L

I guess it is just a marketing scheme.
   -but I bet they'll make tons of money.

Can anyone think of any other reason why nitrogen would leak out of tires slower than air (other than density, obviously)??

[limitboy]

I can't think of a reason, unless its because it is a larger diatomic molecule or has a larger heat of formation.
 
But I have worked in the automotive industry on-and-off for 10 years and I haven't ever seen a case of corrosion or degradation due to air.  Most rims are aluminum or steel alloys which are made to be resistant to oxidation.  Usually iron alone is subject to oxidation and only when there is an electric potential or electrolytic solution.

Now from a physics point of view, the moment of inertia of the tire might decrease with pure nitrogen since it has less mass, but not enough to make a big difference.

I think it is probably a scam by the company.

[DrDick]

[4] Nitrogen is non-flammable: Nitrogen technology has been used in aircraft, military and race car technology for over thirty years.[/color]

 

Air isn't flammable, either.  In order to be flammable, a substance has to react with oxygen.  Air does not combust - it supports combustion of other substances.

Dick

[anthony]

I think I have heard something about filling tyres with noble gases. Diffusion is not the problem on car tyres that it is in inflatable balloons. A noble gas behaves more like a "real gas" making it more elastic and less "lossy". This may make the car more economic over distance.

[Cut Chemist]

I think I have heard something about filling tyres with noble gases.

Nitrogen is not a noble gas.  Noble gas molecules are much larger molecules than nitrogen or oxygen (other than helium), but they are not diatomic. 

My brother is a mechanic, and he said that nitrogen filled tires are claimed to remain at a constant pressure, they do not necessarily stay inflated for longer periods of time. 

For gases, pressure is proportional to temperature.  Perhaps the absence of water vapor might increase the stability of pressure at changing temperatures. 

[loucasa]

You're right that nitrogen is not a noble gas, however, noble gases are smaller, not larger than N₂ or O₂.

 I rather doubt that there are any physical differences between air and pure N₂, since N₂ and O₂ are very similar in size and shape (both diatomics, with N having a slightly larger atomic radius). Thus, both should respond to temperature changes virtually identically. Even the pressure in tires (sorry, American spelling  [] ) is only 2-2.5 times atmospheric pressure, not enough to cause deviations from almost-ideal behavior.

The only advantage I can think of is reduction in chemical oxidation from removal of oxygen, but that seems unlikely to have much effect when the rest of the car is fully exposed to air.

[lightarrow]

You're right that nitrogen is not a noble gas, however, noble gases are smaller, not larger than N₂ or O₂.

It depends on which ones.

I rather doubt that there are any physical differences between air and pure N₂, since N₂ and O₂ are very similar in size and shape (both diatomics, with N having a slightly larger atomic radius). Thus, both should respond to temperature changes virtually identically. Even the pressure in tires (sorry, American spelling  [] ) is only 2-2.5 times atmospheric pressure, not enough to cause deviations from almost-ideal behavior.
The only advantage I can think of is reduction in chemical oxidation from removal of oxygen, but that seems unlikely to have much effect when the rest of the car is fully exposed to air.

As it's already been said, I assume a great advantage is the absence of water wapour.

[Bored chemist]

"As it's already been said, I assume a great advantage is the absence of water wapour."
How come? What harm will water do?
Personally I assume someone is out to make a fast buck.

[lightarrow]

"As it's already been said, I assume a great advantage is the absence of water wapour."
How come? What harm will water do?
Personally I assume someone is out to make a fast buck.

Probably.
However, water vapour, as Cut Chemist already said, causes pressure variation with temperature; in the limit, even because of liquid water condensation.

[Bored chemist]

Could be, particularly if you use a foot pump to fill the tyre normally, but most of the compressors I have seen would provide air that had been somewhat dried (if only because the storage pressure would be higher than the delivery pressure).
At any rate that's an argument for dry air, rather than nitrogen. Dry air is a lot cheaper than N2.

[lightarrow]

Could be, particularly if you use a foot pump to fill the tyre normally, but most of the compressors I have seen would provide air that had been somewhat dried (if only because the storage pressure would be higher than the delivery pressure).
At any rate that's an argument for dry air, rather than nitrogen. Dry air is a lot cheaper than N2.

Is it totally dry?

[Bored chemist]

No, it's "somewhat  dried (if only because the storage pressure would be higher than the delivery pressure)."
But then again, practically nothing is totally dry.

[lightarrow]

No, it's "somewhat  dried (if only because the storage pressure would be higher than the delivery pressure)."
But then again, practically nothing is totally dry.

Ok, however I haven't understood "somewhat dried (if only because the storage pressure would be higher than the delivery pressure)". What do you mean?