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Nitrogen in tires..something occurred to me


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Took my F350 in for service today and had the tires rotated. The truck came with nitrogen filled tires and while I wouldn't order a truck that way, I don't necessarily mind having nitrogen filled tires, at least not until today. I have found in the past that the pressure loss seems much less than with air filled tires.

 

So here's the thing. Tire pressure on the F350 is 65 front, and 80 rear. When the tires are rotated, the rear tires go to the front, and must be adjusted to the 65 psi rating. That means letting out about 20% of the gas in the tire to go from 80 to 65psi. So over the course of time, I will eventually lose all the nitrogen in the tires. So I either forget having nitrogen filled tires, or pay to get them refilled.

 

So if you ever need an argument to not pay for that dealer add-on, here's a good one!

 

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You will have a difficult time getting below 78% nitrogen concentration due to the air you are breathing is 78% nitrogen.

Enough said.

 

 

By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere.

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I am cheap but want my tires full of nitrogen anyway and I have a crafty plan to get there without parting with any of my money.

 

Given:

Nitrogen leaks through rubber tires slower than oxygen.

Air is 78% nitrogen.

 

So I'm filling my tires with regular air and letting the oxygen leak out. As it leaks I refill with plain compressed air. As time passes most of the oxygen will leak out and since I'm only adding 21% oxygen as I refill the tires will keep getting closer and closer to pure nitrogen.

 

:rolleyes:

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Nitrogen is used in aircraft tires because they operate from +100 degrees on the ground to -70 degrees in the air. And aircraft tires are subject to blowouts and fires on landing since Nitrogen doesn't burn.

 

If your truck fits those needs, then spend the money for Nitrogen fills.

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GeorgiaHybrid, you hit the nail on the head. While working tires on that circuit, we always pulled the Schrader valve out after picking up the tires from Goodyear or when Hoosier was providing tires, to get the air out, then refill them with nitrogen. This was done to keep the build-up of pressure to a minimum in order to keep the chassis setup close as possible. I run Michelin XPS Ribs on our fiver with air in them. On our dually I also run air simply because if we set a month or more at one spot I bleed off pressure to smooth out the dually ride. And of course the 78% factor. I'm not racing or flying the rig.

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So a tire is mounted and then filled with nitrogen. Inc it is not mounted in a sealed room filled with nitrogen and the worker is not wearing a breathing device sealed from the room it is impossible to obtain a 100% nitrogen fill. Just a gimic as far as I am concerned.

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Pure nitrogen will also expand less at extreme temps

 

Nitrogen, like all other gases, obeys the so-called Ideal Gas Law where PV = nRT. As a result it expands exactly the same as does oxygen and the trace gases in our atmosphere. The change in pressure of a tire filled with "air" will be virtually indistinguishable from the change in pressure of a tire filled with 100% nitrogen.

 

If you're a geek like me, you can use your TPMS to analyze the change in tire pressure from afternoon when you topped off your tires to the next morning when you started on your trip. The change in pressure can be calculated using T2/T1 where T2 and T1 are the two temperatures (in degrees Kelvin). Not too surprisingly, it comes out pretty close.

 

If the air in the tire has water vapor it is possible to see a decrease in pressure at temperatures below those at which water will crystallize out of the air, but most tires in routine driving will operate in a temperature regime in which the water is in its gaseous state in which case it will behave like other gases. On cold mornings you may be able to see effect of water going from liquid to gaseous states if you look closely at your tire pressures. The tires may exhibit a fast couple of psi increase due, I think, to this phase change occurring.

 

IMHO I see no purpose for nitrogen filling of automotive tires except for increasing the profit margins of tire retailers.

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The real advantage to nitrogen filled tires is that before the air refiner can separate the O2 from the N2 it must be dry so the resultant gas BEFORE the refiner is dry. That will prevent the above pressure changes on cold morning startups due to phase change of water from solid - liquid - gas. It will also reduce or eliminate internal corrosion of the rims, if you are concerned with that sort of thing.

 

Dry gas in the tire is a must if you are using any of the balance bead systems to prevent clumping.

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Nitrogen, like all other gases, obeys the so-called Ideal Gas Law where PV = nRT. As a result it expands exactly the same as does oxygen and the trace gases in our atmosphere. The change in pressure of a tire filled with "air" will be virtually indistinguishable from the change in pressure of a tire filled with 100% nitrogen.

 

If you're a geek like me, you can use your TPMS to analyze the change in tire pressure from afternoon when you topped off your tires to the next morning when you started on your trip. The change in pressure can be calculated using T2/T1 where T2 and T1 are the two temperatures (in degrees Kelvin). Not too surprisingly, it comes out pretty close.

 

If the air in the tire has water vapor it is possible to see a decrease in pressure at temperatures below those at which water will crystallize out of the air, but most tires in routine driving will operate in a temperature regime in which the water is in its gaseous state in which case it will behave like other gases. On cold mornings you may be able to see effect of water going from liquid to gaseous states if you look closely at your tire pressures. The tires may exhibit a fast couple of psi increase due, I think, to this phase change occurring.

 

IMHO I see no purpose for nitrogen filling of automotive tires except for increasing the profit margins of tire retailers.

 

docj, you are correct for pure, dry gasses but atmospheric gas includes water vapor of varying degrees. That is the main culprit in the expansion compared to pure, dry nitrogen.

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The real advantage to nitrogen filled tires is that before the air refiner can separate the O2 from the N2 it must be dry so the resultant gas BEFORE the refiner is dry. That will prevent the above pressure changes on cold morning startups due to phase change of water from solid - liquid - gas. It will also reduce or eliminate internal corrosion of the rims, if you are concerned with that sort of thing.

 

And we have a winner!!! Also aircraft use nitrogen for the same reason (it's dry) AND because they bottles of nitrogen to charge the landing gear struts and hydraulic accumulators can provide the common 400-1500 psi needed.

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Nitrogen is used in aircraft tires because they operate from +100 degrees on the ground to -70 degrees in the air.

 

Aircraft tires are seldom used "in the air", at any temperature.

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Sure got an interesting education from this post!

 

As I said, I didn't ask for the nitrogen, it was already there as one of those ridiculous dealer addons. Seems like from what everyone has said, it really is a waste of money.

 

So then I wonder why the whole concept hasn't failed. (in the auto industry)

 

Thanks all.

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Oh hell, is it that time again for this tread.

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Pure nitrogen will also expand less at extreme temps which is the reason NASCAR teams use it. I plan on keeping our rig under 100 mph so I think I will be OK.

Nope not true. Boyle's Ideal Gas Law disproves that, you can also believe NASA.

 

OOPS. I just realized I'm being redundant, sorry.

 

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docj, you are correct for pure, dry gasses but atmospheric gas includes water vapor of varying degrees. That is the main culprit in the expansion compared to pure, dry nitrogen.

 

I did take water vapor into account in my post. Water vapor is just a gas and obeys the gas laws. The only consideration about water is that it will condense at lower operating temperatures. The fact that the percentage of vapor vapor varies is irrelevant to the fact that the mixture of it and the other atmospheric gases obeys the gas laws like all other gases.

 

If the only thing you wanted to do was eliminate water vapor you could do that without going to pure nitrogen. A dry "air" mixture would be easier and cheaper to achieve than going to pure nitrogen.

 

If you want to pay extra to have nitrogen put in your tires, be my guest. It's surely not going to do any harm and it will make you tire dealer happy.

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If you want to pay extra to have nitrogen put in your tires, be my guest. It's surely not going to do any harm and it will make you tire dealer happy.

If you really want to use it, Get Nitrogen Institute will help you to find it and also to justify it. :P

Good travelin !...............Kirk

Full-time 11+ years...... Now seasonal travelers.
Kirk & Pam's Great RV Adventure

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This old turkey again!

DRY nitrogen is the key.

Not all bottled nitrogen is dry, I have hard bitter experience of this testing delicate systems on ships that required dry nitrogen. The contractor bought nitrogen assuming it was all the same and filled the system up. We soon had strange pressure variations and then corrosion.

So beware, all nitrogen is not dry.

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  • 2 weeks later...

OK, off-topic a bit. Aircraft tires question. Last week the news talking head said airplanes were being diverted from Phoenix airport because it was too hot to land.

I know very little about aircraft, but that sounds questionable to me. If true, would that be because of the tire pressure expansion rate upon landing?

 

2000 Winnebago Ultimate Freedom USQ40JD, ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG retired;Good Sam Life member,FMCA ." And so, my fellow Americans: ask not what your country can do for you--ask what you can do for your country.  John F. Kennedy 20 Jan 1961

 

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