![]() |
The use of Nitrogen for tires is because it is an inert gas that is dryer than the air that comes out of your compressor. We don't worry about the rubber in the tire because it will be replaced long before the moisture breaks down the tire. What we are worried about is the wheel and the bolts that hold the wheel together. The less moisture we can introduce to this area the better... I imagine if you're using a tire with a tube, it really wouldn't matter.
As for the pressure consistency, when I fly from an airport at sea level and land in Denver (let's say), the pressure outside of my tire has changed, there by changing the pressure reading inside of the tire. What kind of gas you use to fill the tire at sea level really doesn't matter... Bottom line, if you have a tube in your tire, it really doesn't matter what you use. If you have tubeless, you may be better off going with nitrogen... IMHO! |
0.02 cents FYI
Large planes: Nitrogen is used because its less of a fire hazard. It not only builds less heat (20% cooler), it's non-combustible, does not feed a fire like air/oxygen will. Not a big factor in a RV's small tires. (There was a loss of a B727 in Mexico because they used air to fill the tire, it blew in the wheel well and created a fatal fire.)
Race cars: With Nitrogen the tire temp stays more stable and therefore pressure is more stable. The other benefits mentioned was drier than air/oxygen and less loss of pressure (leakage is less larger molecule). Also with out the oxidizer (oxygen) it will decay and corrode less. Nitrogen is far better. NASCAR, NASA Space Shuttle and Jet Aircraft can't be wrong, but air is far more convenient. If I had Nitrogen source I'd use that. Nitrogen of course is not NO2 or Nitrous Oxide. NO2 would make bombs out of your tires. Here is a site that is selling Nitrogen for tire filling: http://www.innovativebalancing.com/Nitrogen.htm I remember my old 67 Camaro with steel rally rims got pretty corroded inside. Big fleet operators report tire life increases by 26% and improve fuel economy! I'd say its more of a benefit for your car than your RV. A Nitrogen filling generator station start at about $5,000. You could go buy (rent) a steel tank and fill it with nitrogen at an industrial supply house that would last a long time. |
I have a 1941 9N Ford tractor the rear tires are filled with salt water and air.The tires were replaced in the mid-sixties after 25 years, I now have over 40 years on this set of tires no leaks no problems. So I am not going to worry about a very very small amount of water or oxygen in my small RV tubes.
|
Quote:
|
Quote:
Not hacking on you - but it's true - to a degree. You won't ever actually get to zero oxygen content, but you'll get lower than atmospheric. The mix will asymptotically approach a value of 9% given enough time (assuming 30 psi tire pressure). Remember, the rubber is not one-way - oxygen (and nitrogen, for that matter) can flow BOTH ways. It's the same principle as a reverse-osmosis water membrane. Higher pressure on one side drives the molecules through the membrane (tube/tire) but some molecules flow easier than others. At some point you reach a partial pressure balance where the partial pressure of oxygen in the tire equals that outside the tire, and diffusion is equal in both directions. The nitrogen inside the tire still has net flow out, since it's all under pressure it's partial pressure way exceeds atmospheric, so you'll keep adding more N2/O2 mix. Common rubber compounds used for tires will eventually produce a mix (given enough time) of 89% nitrogen, ~9% oxygen, and 2+% argon (tends to accumulate) with other trace gases. If you have leaky tires the O2% will be higher, because you are introducing more oxygen in your "makeup" air, very airtight tires/tubes will be a lower oxygen percentage. Aircraft (and the space shuttle) that inflate their tires with 100% nitrogen will still have a trace of oxygen in them, due to diffusion INTO the tire from outside air. The partial pressure of atmospheric oxygen is greater than the partial pressure of oxygen in the tire (zero) which results in a net diffusion inflow of oxygen (and argon, CO2, etc etc). |
Nice analysis. I never even thought about the inflow, but I wasn't saying it doesn't happen, just that the business about molecule size is a red herring with regard to our application.
|
If it makes you feel better, Size does not matter?
Quote:
Yes, I grant you molecule size is probably not the reason, as I said, my bad, but it sounded good to me at the time. However for fun, the size (Atomic radius) of AIR's top three elements are: Oxygen 60 pm; Nitrogen: 65 pm; Argon: 71 pm. I confess total ignorance and apathy. :rolleyes: In the case of the tire filtering elements, the Helium, Neon and Hydrogen would be the first to pass out of the tire, if your theory or premise where true. There may be a small truth to it. Clearly Hydrogen and Helium are much smaller molecules, but how they are bonded to the 'air' compound and react with rubber may be another issue. I know one tire company sells "low leak" tubes. People report it keeps pressure better. So the 'AIR' DOES get through the rubber. What elements I don't know, probably as the complete compound minus the water and may be the CO2. However it's a fact 'N' does lose less pressure over time by about a 30% to 40%, compared to "Air". Why, I'll leave that to the chemist but its a fact. I'll buy airguy's explanation, although when it comes to words like osmosis, my eyes glaze over. The distilling property of rubber to turn "Air" compound into constituent gases is a mystery or probably non-existent. However commercial Nitrogen generators use a filter/membrane, taking regular AIR and extracting the N out, partly based on element size. An example membrane: Picture of Nitrogen Generator Filter (Note: If you read how it works, it uses the size of very small micro tubes and inertia to separate air into its elements. Its a flow through process, unlike a tire where the gas is held under pressure in rubber envelope or membrane if you will. So size does matter? Isn't chemistry fun! - not)Does the air pressure in your tire change over time? Yes, but do different elements of the gas compound "Air" escape at different rates, changing the compound? Probably not or not in any significant ratio. Not withstanding airguy's explanation which I have no reason to disagree with, lets say a tire did leak out by elements, a little; you'll never get to the point it becomes 99% nitrogen. If it where to work like that, you would likely end up with CO2 and water left, not Nitrogen. People do report their mounted tires end up full of water, not withstanding "Tractor-man" (with tires that have 3 inches of rubber). There is something there. Clearly the water is getting in but not getting out, and clearly air is leaking out. BTW I am not saying Nitrogen or BUST, I use air. But the properties clearly have benefits. I guess a good second place would be DRY air. |
Tractor tires are filled with water intentionally, to add wieght to the wheels so they don't slip - many, if not most, tractors have the ability to put more power into the wheels than the wheels can transfer to the ground. Additional weight increases the amount of torque you can apply without spinning the wheels. Salt is commonly added to the water to keep it from freezing - trying to drive a tractor with frozen water in the tires will destroy the tires within seconds. Sometimes you will also see large circular weights attached to the axles just outboard of the main tires - same concept.
Most commercial nitrogen generators operate by adsorption (not ABSorption - there is a chemical difference) - they flow pressurized air through a bed of molecular sieve. The molecular sieve adsorbs the nitrogen preferentially onto it's surface, all other gases flow through. When the pressure is dumped on the chamber containing the seive, the nitrogen is released. For oxygen concentrators, the flow-through air is enriched in oxygen (as the nitrogen is stripped off) and is the product, while the nitrogen purge dumps to vent. For nitrogen generators, the oxygen-enriched flow-through gas is dumped to vent, and the nitrogen purge is the product. Same bed of molecular sieve, same process, slightly different plumbing. |
How about using CO2 for tires??
|
Quote:
|
| All times are GMT -6. The time now is 07:11 AM. |