Are Tires Nitrogen-Filled?

$99.00 up charge for nitrogen, really?, you gotta go back and snap a pic of that sticker, so we all can have a good laugh at a dealer who thinks he is selling a "GOOD" deal! Then NEVER buy anything from that lot! There are really competent dealers out there, sadly clowns like this one give ALL dealers a BAD reputation!

 

HAHA! Sorry no one else seemed to have picked up on that...

 

It's an often-used joke around here. We laughed the first couple of times.

Tom

 

Oh, my goodness. The Earth’s atmosphere is composed of the following gaseous stuff: nitrogen (78%), oxygen (21%), argon (1%), and then trace amounts of carbon dioxide, neon, helium, methane, krypton, hydrogen, nitrous oxide, xenon, ozone, iodine, carbon monoxide, and even some ammonia. Lower altitudes, mostly where we live, also contain variable quantities of water vapor.

Knowing that tidbit of information... this is what I've heard about Nitrogen tire fill ups...

The air that is used to inflate tires comes from the same pool that we breathe (see contents above). The "nitrogen" fill air comes from drying this air (decreasing the water vapor) a significant amount. No other change is involved! This lowers the amount of expansion and contraction that normal tire "air" (with normal water vapor content) would be subject to as temperatures rise and fall.

Normal untreated tire "air" would have the about the same water vapor content found in the atmosphere on any given day. Way more in New Orleans and way less in Tucson. Water vapor is a major reason that your tires gain or lose about 1 PSI per 10 degrees of temperature change. The tire's pressure increases as it's heated, and goes down as it's cooled.

Drying the "air" allows this temperature dependent pressure variability to be somewhat lessened... but it really depends on how effective the moisture removal was. Our "normal" day usually includes a diurnal temperature change that moves up in the morning and then heads downward around sunset. The diurnal temperature spread can range from only a few degrees to 40, 50 or even 60 degrees, under certain rapidly changing weather conditions, especially in higher latitudes.

Extremes do happen once in a while. The greatest temperature change in a 24 hour period occurred in Loma, Montana, on the 15th of January, 1972. The temperature in Loma shot up 103 degrees, from 54 below zero Fahrenheit to +49 degrees Fahrenheit. That is actually a world record 24 hour temperature change.

I have experienced a -25 degree F morning warming to +45 degrees F in a 24 hour period when I lived in Whitefish, Mt back in the early '90s. Under that temperatures scenario, a tire inflated to 40 PSI at -25 degrees F could end up at around 46 PSI when the temperature reached 45 degrees F. Not a good outcome, if the max inflation pressure of the tire happened to be rated at 40 PSI. The drier "nitrogen" fill up would keep the pressure increase to a somewhat lower value.

That is what I think I understand about this Nitrogen deal. It really has little to do with nitrogen!

 

Given the fact that air is 78% nitrogen, let's consider the following:

Day 1: Tire is full - 78% Nitrogen + 21% Oxygen + 1% Misc.
Small Oxygen molecules leak out. So now ratio maybe as follows:
Day 2: 80% Nitrogen + 19% Oxygen + 1% Misc
So we put more air in - 78% of the new air is Nitrogen so air in tire will probably end up to be:
Day 3: 78.5% Nitrogen + 20.5% Oxygen + 1% Misc.
Then more Oxygen leaks out, so we put more air in. So on day 4 ratios maybe:
Day 4: 78.75% Nitrogen + 20.25% Oxygen + 1% Misc.
And so on...

You see where I am going with this? It is conceivable that after a number of years and regular fill ups, if one never has flats, tires can get to near 100% Nitrogen, for free...

 

:shocked::shocked:

 

So you're saying the nitrogen air still has normal levels of O2 in it? I've never heard that claim before, do you have something to back that up? Otherwise you'd think they'd call it "dried air", not "nitrogen".

 

Exactly the point I was trying to make. It would be pretty darned expensive to strip the O2 out of the mix... but it's very easy to dry out the moisture.

I happened to be at a local tire dealer a couple or three years ago, getting some valve caps and while I waited in line, I had a short and quite interesting conversation with the person that maintained their "nitrogen" air compressor equipment.

He was very informative, and I have no reason to doubt what he explained.

 

Yes. The product sold in tire stores goes by names such as "Nitronized" - they make no claim that it is pure nitrogen.

Dry nitrogen is used for filling airplane tires and race car tires. For these applications they use liquid nitrogen carried in small dewars, which is part of the attraction: it's easy to wheel out a small dewar as apposed to a big compressor.

The diffusion rate for nitrogen and oxygen is so close that it is practically the same - no advantage there. Dryness is the real advantage.

Tom

 

Here's the ultimate answer- Argon. It's expensive, but you can get it from anyone that welds. The advantage, quantum mechanically speaking, is that it only has one source or internal energy, rotation, and that is small because it's monatomic. Why is that good, the tires will maintain a more consistent temperature (same reason they pump argon between panes of glass, insulation). So if you want the absolute best, most expensive solution, there it is. Or, check your tires every morning for free.

 

Argon is the gas of choice for thermal pane windows for two reasons:

1) It is dry.

2) It is heavier than air.

#2 might not seem like much, but think of this: you have two panes of glass with a thin layer of air between them. You need to remove this air and replace it with a dry gas. How do you do it?

It's not as easy as you might think. If you pull a vacuum you break the glass. If you just pump in the gas it will mix with the air, leaving moisture.

This is where argon comes into play. Being heavier than air, all you do it vent the window at the top and slowly pour the argon into the space between the panes. The lighter air lifts up and floats out of the window.

If you try the same with nitrogen it will mix, being the same density as the major components of air. If you use helium it will float out, although you might be able to reverse the process.

Despite the previous post, argon is not terribly expensive. Being inert and dense, argon gets used over and over. When you let it loose, it stays in the lower atmosphere, where it is eventually extracted and reused.

Not so with helium, which floats up into the upper atmosphere and eventually escapes into space. Because of this, all helium is extracted from the earth. Once it is released, it is lost forever. This makes it fairly expensive.

Tom

 

That's interesting! My last car had green caps as well and was the first car that I'd ever owned with the TPMS and I just thought the green caps had to do with that.
Learn something new all the time...:noidea:

 

This might sound stupid... but can you fill up a tire with green caps with regular air? i.e: mix them? Thanks guys.

 

yes.

 

Costco says the main benefit of nitrogen is the temperature fluctuation over the usage cycle is more stable, (as tires wArm, nitrogen expands less than air would,)
I do not know' what to think!

Costco does not charge extra for this, they just do it sI dont think its a scam. (At least for costco)

 

Do we really think having air on the inside of a tire makes a difference in terms of corrosion? Here is a hint, the outside of the tire and wheel would love to be trapped on the inside with a bit of air that at most has a bit of moisture in it. Now, yes, dry air is better. Nitrogen, Argon, Xenon if you just have insane money to blow, whatever you want, they all make the inside dry.

Here is the easy way to think about water inside the tire. Imagine you have enough water inside so that it is in equilibrium and there is just a touch of liquid sitting at the bottom of the tire. This is not unreasonable, as I've had ice form in some tires on very cold days. (not in years, but way back when I didn't pay attention to this kind of thing.) Okay, so now let's imagine this tire being filled at 0°C to 40 PSI. Of that 40 PSI, .09 PSI is from the vapor pressure of the water. Now heat that tire up to 80°C (I was going to say 100, but I'm sure that people would think something special happens at the "boiling point" when it doesn't.) 80°C is 353K and the pressure of the air goes up the ratio of the beginning and ending temperatures - 353/273 = 1.29 = 51.7 PSI. That is what would happen if the air is completely dry. However, that's not what happens here. The air, which takes up most of the room, brings it up that far, but the vapor pressure of water, assuming there is enough in the tire to keep it saturated adds another 6.9 PSI, bringing the total pressure to 58.6 PSI. That is a 13% increase in pressure. Bringing the tire up to 100°C gives 54.7 and 68.4, for dry and saturated air respectively. Note that the difference is...14.7 PSI, because that is the vapor pressure of water at 100°C. It is also a huge 27% pressure difference when the tires get that hot.

Now, in most cases, you aren't running around with enough water for the air inside to be saturated, at least not when the tires are hot, so this is worst case and depending on the, let's call it dew point for the tire, the effect will be proportionately less. But, it does show why the key thing here is to key the air relatively dry. Emptying your tires of any water that may have accumulated when the weather is cold is a good idea. As is the series trap on your pump, as is draining the compressor's tank, as is not filling your tires in a rain storm if you can avoid it.

I would never pay for Nitrogen in my tires. And if drying the air is called Nitronized, that is pure BS and I'd sue if I had paid money for that. Any decent shop should be keeping the air tank dry. And if the tank is at 140 PSI, the relative amount of water vapor is much less than at 40, so you are most of the way there anyway. (Right? Assume the tank is at 25°C, 140 PSI and saturated, so of the 140, .5 is from the water vapor. The air expands into your tire and you now have 40 PSI. or 1/3.5 the pressure. So the water is not saturated, and can only contribute fractionally. Interestingly, it would be saturated once the temperature got down to about 5°C, hence the point of draining your tires when it is cold.)

I hope that all makes sense. I also hope I didn't make any errors as this was off the top of my head.

Water vapor table via Wikipedia, btw. Vapour pressure of water - Wikipedia, the free encyclopedia

 

Well, I don't know who you talked to at Costco, but the correctly stated benefit of N2 is mainly slower leak rate.
It's nice to have nitrogen but its not worth paying extra for it.

Race car drivers and trucks have additional benefits of fire-proofing. Race car drivers also cannot tolerate moisture, so they could use either dry air or dry N2. But since N2 comes dry that is the choice. Both air and N2 are ideal gases so they have exact same temperature response, but water if present can cause excess pressure at racing tire temperature.

So N2 is good but not for the reason they gave you.

 

Oxidation of tires occurs mostly on the outside where temperatures are greater due to sulight and rotation flexing.
Unless racing, nitrogen has absolutely no benefit to tire life and virtually no effect on permeability. And in racing the coefficient of expansion is noticeably less for pure nitrogen so less changes in tire pressure with increasing speed; unless you want to run at speeds over 100 mph or corner hard the only advantage of nitrogen is profit to the dealer.

 

Costco fills their cars up with nitrogen and I've never had an issue putting normal air in. Some people say the nitrogen handles weather changes better but who really knows?!

 

But at least Costco does not charge extra for it.