Nitrogen in Prius Tires?

[ge49erfan@hotmail.com]

Hi, I am a new Prius owner and I see a lot of talk about changing the tire pressure for better MPG. Will running nitrogen either help or hurt this?

[avdavsim]

<div class='quotetop'>QUOTE(Georgia @ Jul 2 2007, 03:49 PM) [snapback]471755[/snapback]</div>

Hi, I am a new Prius owner and I see a lot of talk about changing the tire pressure for better MPG. Will running nitrogen either help or hurt this?
[/b]

Seeing that the air we get for free is 78% nitrogen and the other major gas, oxygen (21%), is similar in density, I would seriously doubt that the hassle you have to go through to get pure nitrogen in your tires would be worth it.

That's my guess.

[NoMoShocks]

<div class='quotetop'>QUOTE(avdavsim @ Jul 2 2007, 02:02 PM) [snapback]471771[/snapback]</div>

Seeing that the air we get for free is 78% nitrogen and the other major gas, oxygen (21%), is similar in density, I would seriously doubt that the hassle you have to go through to get pure nitrogen in your tires would be worth it.

That's my guess.
[/b]

Thank God, the nitrogen in the tires scam has not made it's way to my region yet, I don't think. I have never heard of it before, other than on Priuschat. And I agree, stay with the free 78 percent nitrogen available from any air compressor near you.

[Betelgeuse]

The conclusions I've come to from reading this site is that nitrogen is better, but the differences are much smaller than the nitrogen hawkers would have you believe. From what I've read, people say that the nitrogen molecule is larger than the oxygen molecule, so it won't leak out through the rubber tires. This means that you don't have to fill up your tires with air as often.

So, if not checking your tire pressure every month is worth the cost of the nitrogen, go for it. If not, then keep filling up with regular air. As far as I can tell (again, this is just gleaned from reading stuff here), there is no additional advantage for "street driving" of the Prius.

[JimN]

<div class='quotetop'>QUOTE(Betelgeuse @ Jul 2 2007, 06:06 PM) [snapback]471825[/snapback]</div>

The conclusions I've come to from reading this site is that nitrogen is better, but the differences are much smaller than the nitrogen hawkers would have you believe. From what I've read, people say that the nitrogen molecule is larger than the oxygen molecule, so it won't leak out through the rubber tires. This means that you don't have to fill up your tires with air as often.

So, if not checking your tire pressure every month is worth the cost of the nitrogen, go for it. If not, then keep filling up with regular air. As far as I can tell (again, this is just gleaned from reading stuff here), there is no additional advantage for "street driving" of the Prius.
[/b]

If "air" leaks out of the tire but nitrogen doesn't then it must be the oxygen leaving. By this reasoning, if you keep your tp up, sooner or later you will have only nitrogen in the tire anyway. Pure nitrogen will help if you drive at 150mph or at 50,000 feet. But Joker gas (from Keaton's BATMAN) is the best.

[qbee42]

<div class='quotetop'>QUOTE(Betelgeuse @ Jul 2 2007, 06:06 PM) [snapback]471825[/snapback]</div>

The conclusions I've come to from reading this site is that nitrogen is better, but the differences are much smaller than the nitrogen hawkers would have you believe. From what I've read, people say that the nitrogen molecule is larger than the oxygen molecule, so it won't leak out through the rubber tires. This means that you don't have to fill up your tires with air as often.

So, if not checking your tire pressure every month is worth the cost of the nitrogen, go for it. If not, then keep filling up with regular air. As far as I can tell (again, this is just gleaned from reading stuff here), there is no additional advantage for "street driving" of the Prius.
[/b]

Oh no! Not another Nitrogen thread!

The diffusion rates for nitrogen and oxygen are very similar, and as already posted, if it was a diffusion problem then the oxygen would diffuse out of the air and diffuse back into nitrogen until an equilibrium was reached. All tires would end up with the same nitrogen/oxygen mixture after a short period of time, regardless of their original fills (if this doesn't make sense to you, look up the term "partial pressure" as it relates to gasses). The real issue is water vapor, which has a considerable volumetric change when it condenses into liquid water. Dry nitrogen contains very little water vapor, so tires filled with dry nitrogen will show less pressure fluctuation verses temperature. Dry air will do the same thing. The "nitrogen" offered by the tire shops is not pure nitrogen, nor is it any drier than air from a good compressor with a water separator. Nitrogen from the tire shops will not hurt your tires, nor will there be any measurable gain. Don't pay extra for it.

Tom

[Betelgeuse]

<div class='quotetop'>QUOTE(qbee42 @ Jul 2 2007, 10:02 PM) [snapback]472019[/snapback]</div>

The diffusion rates for nitrogen and oxygen are very similar, and as already posted, if it was a diffusion problem then the oxygen would diffuse out of the air and diffuse back into nitrogen until an equilibrium was reached. All tires would end up with the same nitrogen/oxygen mixture after a short period of time, regardless of their original fills (if this doesn't make sense to you, look up the term "partial pressure" as it relates to gasses). [/b]

Are you sure about this? What you said sounds plausible, but my little bit of Wikipedia-ing leads me to "Dalton's law of partial pressures" which states that the total pressure of a bunch of ideal gases is the sum of the pressures that the gases would have on their own. OK. But the tires are at a much higher pressure than the surrounding air, so it seems to me that there should be no diffusion into the tire (which would INCREASE the total pressure in the tire and seems completely opposite the direction that diffusion should happen.) But, I'm willing to be proven wrong if you're willing to explain it to me.

Regardless of whether this is correct, I think we both agree that the advantage to using nitrogen is somewhere between zero (you) and very slight (me).

<div class='quotetop'>QUOTE(JimN @ Jul 2 2007, 08:49 PM) [snapback]471972[/snapback]</div>

If "air" leaks out of the tire but nitrogen doesn't then it must be the oxygen leaving. By this reasoning, if you keep your tp up, sooner or later you will have only nitrogen in the tire anyway. Pure nitrogen will help if you drive at 150mph or at 50,000 feet. But Joker gas (from Keaton's BATMAN) is the best.
[/b]

Yes. Assuming that my idea of diffusion across the porous rubber membrane is correct, I think this is true; the nitrogen concentration will increase with time if you just keep adding air.

[Swanny1172]

If you buy your tires at Costco, then they will automatically fill them with nitrogen. However, I don't know how they respond to requests to fill your tires to 42/40 or 44/42 for improved MPG.

If you are getting your nitrogen for free or it is included in the price of new tires, then I say go for it. But, if it is something that you have to pay for, then I say take a pass, because there is absolutely no tangible benefit from running nitrogen in the tires on a passenger car.

[qbee42]

<div class='quotetop'>QUOTE(Betelgeuse @ Jul 3 2007, 12:09 AM) [snapback]472050[/snapback]</div>

Are you sure about this? What you said sounds plausible, but my little bit of Wikipedia-ing leads me to "Dalton's law of partial pressures" which states that the total pressure of a bunch of ideal gases is the sum of the pressures that the gases would have on their own. OK. But the tires are at a much higher pressure than the surrounding air, so it seems to me that there should be no diffusion into the tire (which would INCREASE the total pressure in the tire and seems completely opposite the direction that diffusion should happen.) But, I'm willing to be proven wrong if you're willing to explain it to me.
[/b]

Absolutely sure. What you just quoted is true: the diffusion rate of individual gases is completely independent of the total pressure or the partial pressures of the other gases in the mixture. Looking at our example, increasing the pressure of the nitrogen in the tire only increases the rate at which the nitrogen diffuses out of the tire. It does not reduce the rate at which oxygen diffuses back into the tire (or out, for that matter). Only the relative pressures of oxygen inside and outside of the tire, and the permeability of the tire, control the diffusion rate of the oxygen. Once the partial pressure of oxygen is the same inside and outside of the tire, oxygen stops diffusing through the tire, or more correctly, oxygen diffuses at the same rate into and out of the tire, resulting in zero net diffusion. Double the amount of nitrogen and it makes no difference to the oxygen. The converse is also true, as it is with any ideal gas (in this environment, oxygen and nitrogen both behave as an ideal gas). Water vapor is a non-ideal gas at common temperatures. It easily condenses into water causing large volumetric changes. This is where most of the trouble comes from with using "air" in tires. Air from compressors and tire pumps may contain a fair amount of water.

Now before I get beat up by the nitrogen supporters, let me state that there are advantages to using dry nitrogen in tires in some circumstances:

1) Dry nitrogen contains very little water vapor. As a consequence, it is easier to predict pressure changes as a function of tire temperature. Note that the pressure still changes with temperature, but it does so at a known rate. Race car drivers use this advantage to allow them to tune their tire pressures to withing a fraction of a PSI. They are able to predict tire temperatures based on previous racing experience, which allows them a fine degree of control over tire inflation. They could do the same thing with a gas containing water vapor, but they would need to know how much water vapor the gas contained. It's the uncertainty of the mixture that causes them problems with air (some days are more humid than others).

2) Aircraft also use dry nitrogen to avoid ice build up on the inside of tires. Aircraft tires go through temperature extremes, with hot tires sitting in freezing conditions, leading to off balance ice if any water is present.

3) Nitrogen does not support combustion, which can be important with aircraft and race cars. Normal car tires are not subjected to these extremes.

4) Nitrogen does not promote corrosion. Once again, this is not a big issue with car tires and wheels, which seldom if ever rust or rot from the inside out.

5) Dry nitrogen is readily available as liquid nitrogen. It is easy to have a large amount of high pressure nitrogen on hand. This is one of the biggest reasons it is used in high pressure tires.

The "nitrogen" supplied by tire stores is almost never dry nitrogen from a liquid nitrogen tank. Most stores use a "nitronizer" which increases the nitrogen content of ordinary air. It's still air, just with more nitrogen. We can hope they do a good job filtering out the water vapor so that there is some benefit from running it through the "nitronizer". Plain compressed air from a good system will work just as well, but you don't get the cool green dust caps.

Tom

[Tempus]

Nitrogen is still too reactive.

I recommend using only ARGON for your tires.

And, with a molecular weight of 39.948 for ARGON versus 28.0134 for lowly Nitrogen it will diffuse through the tire walls much more slowly.