Nitrogen in tyres

[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?

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:Me]

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?

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

Not Rotorua.

[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