Nitrogen in tyres

[swbarnett]

Thought I'd start a new thread rather than clog the one this came from.


Pure nitrogen apparently varies in density much less over typical tyre temperature ranges, making it well-suited to inflating tyres when cold and then keeping them at the correct pressure throughout a race meeting, etc.

As far as I know, anyway.
Here's one for the chemists out there.

The ideal gas equation is:

PV = nRT

where P=pressure, V=volume, N=number of moles of gas, R=universal gas constant and T=absolute temperature.

So, for an ideal gas kept at a constant volume (i.e. any gas in a tyre as all gases act pretty much like an ideal gas, so I'm told) as temperature rises so does pressure (at the same rate whatever the gas).

From this it should make no difference which gas is used in a tyre. Or does it? Are people mislead in thinking that Nitrogen expands less than air or am I missing something?

[jrandom]

From this it should make no difference which gas is used in a tyre. Or does it? Are people mislead in thinking that Nitrogen expands less than air or am I missing something?

The key thing, I think, is that the gas equation works on mass as an input variable, not volume, and nitrogen is fairly low mass.

A gas formed entirely of a low-atomic-weight element will obviously require less mass to pressurise a given volume to a certain point than a gas formed of the usual atmospheric mix, which has a fair amount of heavier elements spread throughout.

So if you have a lighter gas at a certain pressure in a certain volume, a given change in temperature will result in less expansion or contraction than what you'd get from a heavier gas which started at the same pressure in the same volume.

[R6_kid]

doesnt each gas have its own expansivity constant? Hence why the equation works for an 'ideal gas' which is theoretical.

[jrandom]

doesnt each gas have its own expansivity constant?

Yeah.

It's in direct proportion to how heavy it is.

[jrandom]

... why the equation works for an 'ideal gas' which is theoretical.

The only difference between the 'ideal' gas and a real gas is the fact that the 'ideal' gas equation doesn't consider friction, which would be a vanishingly small term in the equation in any case.

The ideal gas equation still works on the mass of the gas as an input, which makes it applicable to anything.

[vifferman]

Air is 78% nitrogen anyway.
The critical thing with using nitrogen rather than compressed air may be the dryness of the air. From memory, I think the nitrogen used has a lot less moisture and other crap in it than your average compressed air. The moisture heating up and becoming gaseous or cooling down and condensing will possible affect things more than minor elements like hydrogen or methane or whatever misbehaving and wandering off to have a carcase meeting of the executive or whatever the naughty little molecules get up to.

[CookMySock]

Air is 78% nitrogen anyway.LOL Chawp!!! :Pokey:

DB

[jrandom]

The moisture heating up and becoming gaseous or cooling down and condensing will possible affect things more than minor elements like hydrogen or methane or whatever misbehaving and wandering off...

Damn your practicality, sir. We were having fun considering that particular spherical cow.

[Badjelly]

Here's a few links found with Google:

http://www.racq.com.au/cps/rde/xchg/racq_cms_production/hs.xsl/Motoring_Maint_Repairs_Foun_factsheet_nitrogen_tyr es_ENA_HTML.htm
http://www.tyresave.co.uk/nitrogen.html
http://www.blackcircles.com/general/technology

The last one says "oxygen permeates three times faster than the nitrogen". That's the only explanation that makes any sense to me.

[Badjelly]

The only difference between the 'ideal' gas and a real gas is the fact that the 'ideal' gas equation doesn't consider friction

...and finite size of the molecules, but nothing that matters for oxygen or nitrogen at ordinary temperatures and pressures.

[ManDownUnder]

Filling automotive (http://en.wikipedia.org/wiki/Automotive) and aircraft (http://en.wikipedia.org/wiki/Aircraft) tires (http://en.wikipedia.org/wiki/Tire)<SUP class=reference id=_ref-4>[5] (http://en.wikipedia.org/wiki/Nitrogen#_note-4)</SUP> due to its inertness (http://en.wikipedia.org/wiki/Inertness) and lack of moisture (http://en.wikipedia.org/wiki/Moisture) or oxidative (http://en.wikipedia.org/wiki/Oxidative) qualities, as opposed to air (http://en.wikipedia.org/wiki/Air), though this is not necessary for consumer automobiles (http://en.wikipedia.org/wiki/Automobiles).<SUP class=reference id=_ref-5>[6] (http://en.wikipedia.org/wiki/Nitrogen#_note-5)</SUP><SUP class=reference id=_ref-6>[7] (http://en.wikipedia.org/wiki/Nitrogen#_note-6)</SUP>
Nitrogen molecules (http://en.wikipedia.org/wiki/Molecules) are less likely to escape from the inside of a tire compared with the traditional air mixture used. Air (http://en.wikipedia.org/wiki/Earth%27s_atmosphere) consists mostly of nitrogen and oxygen (http://en.wikipedia.org/wiki/Oxygen). Nitrogen molecules have a larger effective diameter (http://en.wikipedia.org/wiki/Diameter) than oxygen (http://en.wikipedia.org/wiki/Oxygen) molecules and therefore diffuse (http://en.wikipedia.org/wiki/Diffuse) through porous (http://en.wikipedia.org/wiki/Porous) substances (http://en.wikipedia.org/wiki/Chemical_substance) more slowly.<SUP class=reference id=_ref-7>[8] (http://en.wikipedia.org/wiki/Nitrogen#_note-7)</SUP>

[Badjelly]

Looking up Wikipaedia, that's cheating!

[jrandom]

Right, Google tells me that the molar mass of atmospheric air is about 29 g/mol, and nitrogen's is about 14 g/mol.

In other words, Earth's atmospheric mix is, on the whole, twice as dense as pure nitrogen. Intuitively, I'd think that that would make quite a difference in rates of expansion.

I have to do some proper work now, so if anyone wants to pull some other numbers out of their arse, plug those into the gas equation and find out what the differences in rates of expansion over typical tyre operating pressures are for typical motorcycle tyre volumes, be my guest.

Otherwise I'll do it when I get home tonight...

[Badjelly]

Right, Google tells me that the molar mass of atmospheric air is about 29 g/mol, and nitrogen's is about 14 g/mol.

The second figure is for monatomic nitrogen (N), not diatomic nitrogen (N2). Diatomic nitrogen is the form that occurs in the atmosphere.

Air is a mix of 80% N2 (28 g/mol) and 20% O2 (32 g/mol), hence its molar mass is roughly 29 g/mol. So the difference between air and pure N2 is not large.

I think ManDownUnder has answered the question for us.

[jrandom]

The second figure is for monatomic nitrogen (N), not diatomic nitrogen (N2). Diatomic nitrogen is the form that occurs in the atmosphere.

Ah. I didn't realise that we were talking about filling tyres with N2.

OK, moisture is the culprit...

[Badjelly]

Ah. I didn't realise that we were talking about filling tyres with N2.

It's pretty hard to get any other sort!


OK, moisture is the culprit...

Yeah, but in that case you could use any dry gas, including dried air.

I think the lower diffusion rate is the main thing.

[jrandom]

It's pretty hard to get any other sort!

Oddly enough, having just last year written some control software for a simulated altitude training machine, you'd think I'd remember that little detail, wouldn't you?

:o


I think the lower diffusion rate is the main thing.

But I thought thermal stability was a big selling point, which, if it's not due to density, must be due to dryness?

[swbarnett]

WOW! KB is more learned than I thought (although with 10,000 members I guess you might expect a brain cell or two).

Thanks heaps for the replies.

My wife lectures Thermal Physics (among other things) at Auckland Uni. and we came to a stalemate on this. Never thought of the moisture!

Guess our minds must be too highly trained, Magicthies!

[Forest]

There's a Ferrari touring car racing team in the warehouse next to me.

According to the head mechanic they use nitrogen to prevent moisture getting into the tyres.

He also said that when they go racing, they use nitrogen tanks to power their workshop air-tools.

[Hitcher]

What causes all of the air in a tyre to suddenly rush to the top? Is that Henry's Law at work or something altogether more sinister?

[R6_kid]

What causes all of the air in a tyre to suddenly rush to the top? Is that Henry's Law at work or something altogether more sinister?

I thought it was 'nail in the tyre syndrome'?

[jrandom]

What causes all of the air in a tyre to suddenly rush to the top?

That would, of course, be due to the lower half of the wheel rotating faster than the upper half.

[Badjelly]

But I thought thermal stability was a big selling point
Yes, but what do you (or the people selling the nitrogen) mean by thermal stability?

[GSVR]

Filling your tyres with Nitrogen is a good way to get better performance and safety from your tyres. Nitrogen will leak three or four times more slowly than compressed air, which can lead to some pretty useful benefits like:

Stable tyre pressure.
Improved road grip.
Safer all-weather performance.
Increased fuel economy.
No internal oxidisation through the elimination of moisture.
Increased tyre life.
Harder Longer erections.
Better Sex life.
Higher income.


http://www.firestone.co.nz/services/detail/nitrogen

[jrandom]

Yes, but what do you (or the people selling the nitrogen) mean by thermal stability?

A low coefficient of thermal expansion; big temperature change = small pressure change.

I'd imagine that having water suspended in the mix, alternately condensing and vaporising, would be a pretty effective way of raising that term.

[martybabe]

That would, of course, be due to the lower half of the wheel rotating faster than the upper half.
is that true if the lower half had nitrogen and the upper half had air?:confused:


Yes, but what do you (or the people selling the nitrogen) mean by thermal stability?

Not Rotorua. :shifty:

[Badjelly]

A low coefficient of thermal expansion; big temperature change = small pressure change.

OK, well that's one thing nitrogen (or any other gas) definitely doesn't offer, because of the ideal gas law.


I'd imagine that having water suspended in the mix, alternately condensing and vaporising, would be a pretty effective way of raising that term.

Does moisture ever condense in tyres? I'm not sure. If it did, it would have the effect of raising the thermal expansion coefficient. It might also rust the steel belts (if any). Condensed moisture in your tyres could hardly be a good thing.

[spudchucka]

Firestone tried to sell me nitrogen recently when I put a couple of new tyres on the coon, $5 per tyre, thanks but I'll just stick to the free stuff from the servo thanks.

[Badjelly]

Firestone tried to sell me nitrogen recently when I put a couple of new tyres on the coon, $5 per tyre, thanks but I'll just stick to the free stuff from the servo thanks.
Good call. The $5 charge is a tax on gullibility.

[Mikkel]

Here's one for the chemists out there.

Hmm, thermodynamics are just as much the playing field of physicists and engineers mind you...


The ideal gas equation is:

PV = nRT

where P=pressure, V=volume, N=number of moles of gas, R=universal gas constant and T=absolute temperature.

P*V = mass.

In a tyre you have to consider the mass constant. The volume is close to being constant. The effect of raising the temperature will mainly be an increase in pressure -> smaller contact patch -> less rolling resistance.

Of course there are numerous assumptions included in that equation as has been outlined in previous posts. For most intents and purposes it describes the behaviour of gasses rather well.


From memory, I think the nitrogen used has a lot less moisture and other crap in it than your average compressed air. The moisture heating up and becoming gaseous or cooling down and condensing will possible affect things more than minor elements like hydrogen or methane or whatever misbehaving and wandering off to have a carcase meeting of the executive or whatever the naughty little molecules get up to.

I'm thinking you hit the nail spot on there! Water expands about 1400 times when going from liquid to gas phase. However, the phase transition takes a fair amount of energy and may actually help to cool the tyre - for a while.

Another thing to bear in mind is that modern soft compound race slicks are quite porous and will leak air, and nitrogen for that matter, very quickly. You would always check your tyre pressure before hitting the track in any circumstance. Thus, the use of nitrogen to reduce leakage for performance tyres is a bit redundant.


Right, Google tells me that the molar mass of atmospheric air is about 29 g/mol, and nitrogen's is about 14 g/mol.

In other words, Earth's atmospheric mix is, on the whole, twice as dense as pure nitrogen. Intuitively, I'd think that that would make quite a difference in rates of expansion.

Molar mass and volume specific mass density are not the same thing mind you. Besides for gasses (due to the above equation) density depends very much upon their pressure and temperature.


That would, of course, be due to the lower half of the wheel rotating faster than the upper half.

DO NOT GO THERE!


(no mention of rotating bodies)

Phew, I think we dodged that one ;)


Does moisture ever condense in tyres? I'm not sure. If it did, it would have the effect of raising the thermal expansion coefficient. It might also rust the steel belts (if any). Condensed moisture in your tyres could hardly be a good thing.

There's likely to be some water in liquid phase in your tyre. Albeit, it will not be in a pool in the bottom of the tyre - just tiny droplets suspended in the air. When the temperature increases a fraction of this is going to undergo a phase transition to gas phase and expand those ~1400 times...
Don't worry about it ;)

[jcupit69]

if memory serves correct the new nissan GTR had special tyres designed for it that are filled with nitrogen???

[boman]

We used to fill our transam light tyres up with nitrogen. We found that the pressure did not increase as much when the tyre was hot, as it did when using compressed air. This was handy so you did not have to worry about the pressure altering the tyres contact patch during a race. On a road car, ,if my memory serves me correctly, the pressure can increase by around 5 - 10 psi during normal driving. Which is why you should always check tyre pressures COLD not after they have been driven on.


:done:

[vifferman]

Nitrogen in tyres kills baby fur seal whales and causes globular yawning.
It's chock full of carbon, y'know, which is why tyres are black. :baby:

[Badjelly]

We used to fill our transam light tyres up with nitrogen. We found that the pressure did not increase as much when the tyre was hot, as it did when using compressed air.

Are you sure about that? Because the ideal gas law tells us that the change in pressure due to a given change in temperature is the same for any gas. (Well, any ideal gas, but air and nitrogen are pretty much ideal gases.) So either your observation is incorrect or there's something else going on. And the only something else that I can think of, that's been mentioned on this thread and might be relevant, is that an increase in temperature causes condensed water to evaporate.

[Mikkel]

Are you sure about that? Because the ideal gas law tells us that the change in pressure due to a given change in temperature is the same for any gas. (Well, any ideal gas, but air and nitrogen are pretty much ideal gases.) So either your observation is incorrect or there's something else going on. And the only something else that I can think of, that's been mentioned on this thread and might be relevant, is that an increase in temperature causes condensed water to evaporate.

Air is pretty much nitrogen...

If you read some of the earlier posts it seems that moisture in air compared to clean dry nitrogen is what makes the difference. Water expands a lot when it evaporates.

[Badger8]

ergh, it's late, i'm tired... 5 minute try...

PV = nRT, assume ideal gas law holds (which at the pressures we're talking about, is near enough to true), Less mass to cause sufficient pressure. Look up coefficient of thermal expansion in Perry's Chemical Engineering Handbook, compare it to that of typical atmosphere (or calculate it out at ratios if needs be) even at the not-atall-accurate 80-20 N2 O2 mix (78-16 off the top of my head?) ya can see the difference. it may be sod all, but to some people it's enough to justify it.
Plus there were other benefits mentioned, cant be bothered reading it all. There's some real crap in the air comin outta gas station compressors too.

Ergh, if i dont wanna think about this crap at work when i'm gettin paid to do it, why on earth am i doing it now for free? :eek5:

[98tls]

Simple really,anyone that rides a road bike on a public road in this country that thinks there is anything to be gained by inflating there tyres with it deserves to move themselves to the states and have the pleasure of being dumb enough to pay for someone else to fill there tyres with it.

[Mikkel]

Saw the thread and thought. "Today is indeed repost day." Turns out today is thread necromancy day...

I'm pretty laid back, 78-80% nitrogen is good enough for me.

[Hitcher]

Turns out today is thread necromancy day...

Indeed there's nothing like a bit of romantic foreplay to get one's day off to a good start.

[Kickaha]

Simple really,anyone that rides a road bike on a public road in this country that thinks there is anything to be gained by inflating there tyres with it deserves to move themselves to the states and have the pleasure of being dumb enough to pay for someone else to fill there tyres with it.

So how do you know without trying it that there is nothing be gained from it?

There is tens of thousands of dollars spent each month in this country putting it in cars, if all those people moved to the States the country would empty reasonably quickly

[98tls]

So how do you know without trying it that there is nothing be gained from it?

There is tens of thousands of dollars spent each month in this country putting it in cars, if all those people moved to the States the country would empty reasonably quickly And that would be a bad thing?:shutup:After reading many threads on many bike forums the world over with many posts by some pretty clued up buggers ive never yet seen one post mentioning any benefit to filling tyres in vechicles used under everyday road going conditions so to pay for such a service would seem to me anyway a waste of $

[imdying]

So how do you know without trying it that there is nothing be gained from it?Because he's not a retard.

There is tens of thousands of dollars spent each month in this country putting it in cars, if all those people moved to the States the country would empty reasonably quicklyYep, that would be the aforementioned retards.

[Crazy Steve]

You are all wrong ya bunch of muppets.....

And you dont need to be a chemist to figure it out...

Im a truckie and have the answer...:2guns:

Crazy Steve..

Ps...you are all a bunch of slaves...:wacko:

[MaxCannon]

From what I've read in magazines and the like the key benefit with Nitrogen is the lack of water vapor compared to normal air.
In a racing situation water heats to boiling point.
Usefull for hot water bottles, not useful inside tyres.

If you are riding hard enough on the road to get the water vapor in your tyres boiling then changing it for Nitrogen will probably get you more consistent pressure and therefore a better gripping / feeling tyre.

Although you'd probably need it since going that hard is going to get some blue and red lights on your tail.

[98tls]

From what I've read in magazines and the like the key benefit with Nitrogen is the lack of water vapor compared to normal air.
In a racing situation water heats to boiling point.
Usefull for hot water bottles, not useful inside tyres.

If you are riding hard enough on the road to get the water vapor in your tyres boiling then changing it for Nitrogen will probably get you more consistent pressure and therefore a better gripping / feeling tyre.

Although you'd probably need it since going that hard is going to get some blue and red lights on your tail. :Oi:FFS there will be all these late model Ducati owners up all night squeezing themselves into billon dollar leathers convinced they have to have some,be a hell of a thing to park up and have a latte without nitrogen in your rubberbands.:rolleyes:oh the humanity.

[Gixxer peter]

hmm if oxygen leaks out faster than nitrogen then if you fill it with air and some leaks out then, the oxygen is most likely to come out leaving the nitrogen, do this several times and then you mostly have nitrogen in your tires.
Yahoo i got it???
right?/