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Nitrogen filled tyres

graeme on Wed October 05, 2005 6:36 PM User is offline

Just been reading all the trash about filling tyres with nitrogen and the supposed advantages. As far as I could tell, the idea is to stop any water from getting into the tyre, which when it condenses will lower the pressure of the tyre or when it evaporates will increase the pressure of the tyre by a few psi. Using completely dry normal air would theoretically achieve the same thing.
This brings me to one claimed advantage in that nitrogen leaks through a normal tyre membrane at one third of the rate of oxygen and would only need occasional topping up with this expensive pure nitrogen. It was mentioned in a thread a while ago about how water molecules at 1 atm could seep into an ac system under much higher pressures until the amount of water inside the ac matched the outside concentration, admittedly a concept I have trouble with.
Anyway, applying the same principles to the tyre, wouldnt over time moisture and oxygen seep back into the tyre, requiring the need for the tyre to be evacuated and refilled with nitrogen to maintain its supposed virtues?
Would the ridiculous occur? If tyre was filled to 1atm(not 1atm above air pressure) with nitrogen and allowed to sit for a few years, then the pressure would build up 20% due to the invasion of oxygen and the remaining atmospheric gases and the tyre would then have a reading of 3psi when checked with a tyre gauge?

Karl Hofmann on Wed October 05, 2005 7:09 PM User is offlineView users profile

The density of Nitrogen changes to a lesser degree due to temperature fluctuations, and so the pressure does not change as much when in service

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Never knock on deaths door... Ring the doorbell and run away, death really hates that!

graeme on Wed October 05, 2005 8:08 PM User is offline

Dont know what you mean Karl?
The density of any gas inside the tyre is not going to change with temperature - as the same amount of gas(mass) is inside with basically the same fixed volume(the tyre case). Only the pressure can change with temperature, and I cant think of a good reason why nitrogen would be any different to any other gas in following the real gas laws. Its also claimed that nitrogen makes the tyres run cooler, theres not a lot of difference in the heat capacity of oxygen and nitrogen gas and basically the mass of gas inside the tyre is neglible compared to that of the wheel and tyre so I dont know how it could accomplish that either, somehow reduce friction with the road and tyre?

NickD on Wed October 05, 2005 10:50 PM User is offline

Ha, I know a lot of folks that would benefit by simply putting air in their tires, like Graeme, thought all gases followed the same laws, but would have to look that up in my physics book regarding the thermal expansion of oxygen versus nitrogen. Air is 80% nitrogen anyway, so not like comparing pure oxygen with nitrogen. What about filling your tires with hydrogen, would save some weight and let the wheel respond better to the countless bumps in the roads. Well, helium would be safer, right HC refrigerant guys?

Only thing I know of other than air is filling tires water with 28% of that weight with calcium chloride mixed in for a cheaper -60*F freezing point. Very common in my neck of the woods to fill driven tractor wheels with that solution to gain more traction, does work and the farmers were doing that for years.

Ha, I like filling my tires with my own air compressor, has a dryer on it, don't want water in my tires splashing around, car tires that is.

graeme on Thu October 06, 2005 5:09 AM User is offline

Nick, save you the trouble of looking up those text books, the theories of Charles and Boyle took care of the question over 200 years ago. There are no expansion coefficients etc for gases, they all obey one equation PV=nRT, all gases expand by the same amount when heated, nitrogen too.
Re other gases and weight, its not really worth the trouble, the mass of air inside a typical tyre is only 70grams. Insignificant compared to the mass of the tyre and wheel.

NickD on Thu October 06, 2005 6:51 AM User is offline

What clicked in this tired old head are the P-T curves for R-12 and R-134a that are also gases in the higher temperature ranges. PV=nRT is a linear equation and should produce a straight line graph when plotting pressure versus temperature, but not exactly the case with R-134a, at the higher end of the curve, the pressure of R-134a actually increases faster than the temperature producing a curved rather than a straight line graph. And perhaps oxygen mixed in with nitrogen was doing the same thing. R-12 pressures still swings upward with increases in temperature to avoid that straight line characteristic, but not as fast as a rate as R-134a. I am not aware of P-T curves for gases in their elementary form such as nitrogen nor oxygen.

If I had to choose between filling my tires between R-12 and R-134a, would be R-12 as R-134a could explode the tire at higher temperatures, but both would be dead flat at -20*F. Suppose if a guy were bored, could really make an issue of what to fill a tire with.

Guess this can get to be a complicated issue when one considers atmospheric pressures and ambient temperature conditions particularly in aircraft tires that experience board ranges in both parameters. Heat causes both the tire to expand that decreases volume and likewise the rubber becomes more flexible allowing for a further increase in volume. But they just say, check your tire pressure under normal conditions before taking off. And to the best of my knowledge, they just use air.

Ha, knew people that wanted their tires deflated and fresh air put it, claimed it gave a smoother ride.

JJM on Thu October 06, 2005 3:15 PM User is offline

I too have been hearing a lot of hype about filling tires with nitrogen, and frankly I don't see the benefit. As NickD pointed out, air is about 80% nitrogen anyway... and it doesn't cost anything! I too agree if you have a filter/vapor seperator on your compressor, you're fine, so what's the benefit -- other than fattening the wallets of those selling this "service."

It is amazing just how much temperatures affect tire pressures. Tire pressure can be 30 PSI on all the wheels first thing in the morning, but after extended driving high speed driving on a hot afternoon, it's kind of odd to see the "Check Tire Pressure" message on the dash, then scrolling down to see that some of the tires are at 38-39 PSI. I understand tire pressure monitoring is mandated on all 2006 vehicles, though this Chrysler minivan I was driving was constantly flashing a tire icon at me, even though all the tires were filled to spec. Then there's the problem of getting tire shops that don't destroy the sensor when dismounting the tire, and having a scan tool to reprogram the wheel positions.

Joe

graeme on Thu October 06, 2005 5:51 PM User is offline

regs for passenger airlines, state no more than 5% oxygen for the tyres. Aircraft tyres catching fire are a reality if brakes are overloaded, rough landings etc, so it pays not to have too much oxygen around that could be released to fuel the blaze.

HerkyJim on Thu October 06, 2005 6:54 PM User is offline

Quote
Originally posted by: graeme
regs for passenger airlines, state no more than 5% oxygen for the tyres. Aircraft tyres catching fire are a reality if brakes are overloaded, rough landings etc, so it pays not to have too much oxygen around that could be released to fuel the blaze.

Hmmm, don't see anything about nitrogen inflation of airplane tiresin my old FAA "Airframe & Powerplant MECHANICS AIRFRAME HANDBOOK". Is this something recent? Must be in the FARs. Wonder which one?

Theep Dinker on Fri October 07, 2005 12:45 AM User is offline


Well, the mech and powerplant handbooks were written when? 1950? Things have changed. Landing weights and speeds are much higher these days. The airline I work for uses N2 fills due mainly to the fire hazard mentioned above. Also used in struts. There are other factors involved too, like weather-checking and oxidation. O2 is bad news for almost everything excpet keeping us alive. Just proves God has a sense of humor. Also TSO'ed or certified tires are usually tubed and have lots more latex in thier compounding than other types. There is lots of petroleum in automotive tires for example. I also use N2 on my C177RG and L39. I could get away with air in the RG as most do but I'd never use it in the Albatros. I use N2 in the Cessna because I have it around for other things and because the Cessna doesn't use Skydrol for the gear and brakes. Using it for cars seems more trouble than it's worth though.

Edited: Fri October 07, 2005 at 12:48 AM by Theep Dinker

graeme on Sat October 08, 2005 3:02 AM User is offline

Quote
Originally posted by: JJM
I too have been hearing a lot of hype about filling tires with nitrogen, and frankly I don't see the benefit. As NickD pointed out, air is about 80% nitrogen anyway... and it doesn't cost anything! I too agree if you have a filter/vapor seperator on your compressor, you're fine, so what's the benefit -- other than fattening the wallets of those selling this "service.

It is amazing just how much temperatures affect tire pressures. Tire pressure can be 30 PSI on all the wheels first thing in the morning, but after extended driving high speed driving on a hot afternoon, it's kind of odd to see the "Check Tire Pressure" message on the dash, then scrolling down to see that some of the tires are at 38-39 PSI. .



Joe

An increase of 9psi?(well you didnt specify any temperatures) but if the tyre started at 77F and finished 9psi higher then the temp of the tyre would be 171F. This would be way too hot hold a hand against, do the tyres feel that hot? On possibility is that you are experiencing this large change of pressure(about 3psi of it) due to the vaporisation of water within the tyre, rather than overall temp increase of the tyre.

NickD on Sat October 08, 2005 7:57 AM User is offline

Even up here, on a hot sunny day, black asphalt can easily hit 180*F, can fry an egg on it, so 170*F tire temperature does not sound unreasonable. Many of our roads are being blacktopped, concrete doesn't like the huge temperature changes and really hates road salt. One very simple solution would be for everyone to work and go to school at night and sleep during the heat of the day.

brickmason on Sat October 08, 2005 9:31 PM User is offline

Quote
Originally posted by: NickD
Even up here, on a hot sunny day, black asphalt can easily hit 180*F, can fry an egg on it, so 170*F tire temperature does not sound unreasonable. Many of our roads are being blacktopped, concrete doesn't like the huge temperature changes and really hates road salt. One very simple solution would be for everyone to work and go to school at night and sleep during the heat of the day.

Did you know that asphalt,(especially asphalt driveway's), when having coastal bermuda grass adjoining them will crumble the sides in a couple years time because of the root mass being so strong?

Have seen them destroy as far as a foot or more in from each side because of this. So if you plan on having a driveway asphalted and have a yard full of bermuda, better keep it's root system from getting under it.

As far as everyone working at night may work for city folk but would be kinda hard to do down here in farm country.

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Just another brick in the wall

Had a little mule I fed him castor oil and every time he jumped the fence he fertilized the soil

NickD on Sat October 08, 2005 9:59 PM User is offline

How many farmers do you know that drive to work? LOL

brickmason on Sat October 08, 2005 10:35 PM User is offline

Quote
Originally posted by: NickD
How many farmers do you know that drive to work? LOL

Quiet a few of them drive to work Nick.
If a farmer owns a thousand acres, then it would be foolish to walk to the farther edge of his property when he can drive his tractor or truck along the roadway to get there.

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Just another brick in the wall

Had a little mule I fed him castor oil and every time he jumped the fence he fertilized the soil

brickmason on Sat October 08, 2005 10:43 PM User is offline

We also have insurance companies called Farm Bureau where farmers can insure their trucks for half price or less than what it would cost for typical road errand use.

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Just another brick in the wall

Had a little mule I fed him castor oil and every time he jumped the fence he fertilized the soil

JJM on Sat October 08, 2005 11:41 PM User is offline

It was on a trip to NY from south FL. By mid afternoon, the temps were in the mid-90's, and with four lanes of I-95 wide open, it was hard not keep speeds out of the triple digits... sometimes to the point where this "Top Speed Fuel Cut-Off" message (130 MPH) appeared a few times on the dash. I suppose this was a bit too much for the factory H-rated tires. I also understand that this threshold can be bumped up with a Tech2 if higher speed rated tires are installed, like V or Z, but you don't buy a car like that for high performance.

Never really realized just how much tires pressures vary until this little gizmo, especially going into the winter months! That thing is always bothering me, until we stabilize at sub freezing temps.

Now if only they can devise a system that automatically adjusts tire pressure also...

Joe

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