Tire Pressure - Nitrogen vs. Air ?

[Zandy595]

If you have nitrogen in your tires, should the pressure be higher than if you have plain air?

 

[FlightlessDuck]

How much nitrogen should I put in my tires?

Simply inflate your tires with nitrogen to the vehicle manufacturer's recommended psi for air. There is no conversion factor necessary for filling tires with nitrogen vs air. GNI recommends inflation pressures as stated in the vehicle owner's manual or posted inside the driver's door of the vehicle, and maintaining this pressure in order to optimize your fuel economy, tire life, and vehicle handling.

http://www.getnitrogen.org/sub.php?view=getTheFacts&subpage=psiconversion

After all, psi is still psi, regardless of the gas. It might take MORE nitrogen for the same psi. Or less (I'm not a chemist...)

 

[bcla]

If you have nitrogen in your tires, should the pressure be higher than if you have plain air?

Should be no difference.

That being said, paying for nitrogen seems like a waste to me and is heavily oversold by tire dealers. Ordinary air is 80% nitrogen, and there's really no cost-effective way to purge a tire of all its air. They get filled with nitrogen at Costco, but I like to be able to top off wherever I need it. There's also nothing particularly damaging about oxygen inside a tire. Modern tires have an inside sealing layer that is separated from the rubber and that doesn't oxidize. Oxygen from the tires leaks so little into the rubber compared to atmospheric oxygen.

Aircraft tires need nitrogen to reduce the risk of fire, but they don't use the relatively cheap equipment that are used at tire dealers. They use canister nitrogen from gas supply houses. There's pretty much no risk of a car tire catching on fire because it wasn't filled with nitrogen.

 

[Zandy595]

I would rather not have nitrogen in our tires (it's a pita when something like this happens), but DH will believe anything a salesman or mechanic tells him.

It's been in the 80°s here, but we had a couple nights where the low got down to 50° and my son's tire indicator light came on. All four tires were low, so I told DS we could fill them up with regular air. He didn't have time to go get nitrogen. We put 30 psi in them because that's what it says on the inside of the car door. DH says the mechanic recommends 35 psi and wants DS to go have more nitrogen put in them because he says every time it gets cold now the light will come on. DS thinks it's a waste of time and doesn't want to do it. I agree with him, but DH won't let it go.

 

[Cannot_Wait_4Disney]

I would rather not have nitrogen in our tires (it's a pita when something like this happens), but DH will believe anything a salesman or mechanic tells him.

It's been in the 80°s here, but we had a couple nights where the low got down to 50° and my son's tire indicator light came on. All four tires were low, so I told DS we could fill them up with regular air. He didn't have time to go get nitrogen. We put 30 psi in them because that's what it says on the inside of the car door. DH says the mechanic recommends 35 psi and wants DS to go have more nitrogen put in them because he says every time it gets cold now the light will come on. DS thinks it's a waste of time and doesn't want to do it. I agree with him, but DH won't let it go.

There is no way 50 degrees is causing the moisture in your air to condense and freeze at such a rate as to lose that much pressure. Airliners use nitrogen because any moisture content in it won't freeze at the altitudes they fly and for fire safety because of the intense heat generated by take offs and landings. Mexicana Flight 940 crashed because a tire was filled with regular air instead of nitrogen.

 

[Gumbo4x4]

Air pressure decreases with colder air. The advantage of nitrogen vs "air" is that this effect is much less dramatic with nitrogen.

 

[SkaGoat]

Air pressure decreases with colder air. The advantage of nitrogen vs "air" is that this effect is much less dramatic with nitrogen.

but this also means that people who live in areas that don't have drastic shifts in temperature don't see as much benefit from Nitrogen in their tires.

The temperature in my part of the world is up and down like a toilet seat this time of the year (Can drop 20 degrees in one day), and it can cause issues. I use regular old air in both my vehicles, but that's more because I'm cheap, than whether it's effective or not.

But your mechanic has given bad advice, you shouldn't over-inflate your tires, this can cause handling issues with your vehicle.

 

[bcla]

Air pressure decreases with colder air. The advantage of nitrogen vs "air" is that this effect is much less dramatic with nitrogen.

Not really. The pressure difference between the 98% nitrogen and a typical air mixture (especially dry air) will be virtually linear with any kind of reasonable temperature. The only possible difference is that the input from water vapor will go to zero once it turns to liquid and/or ice. The amount of water vapor isn't going to cause a dramatic loss in pressure.

The ideal gas law is PV = nRT - or pressure * volume = amount of gas * universal gas constant * absolute temperature. Unless it's getting so cold that this gas is turning to liquid (or solid) it's not going to cause anything dramatic to happen.

The main benefit of generated nitrogen may be that it's relatively free of moisture. However, it's possible to get "dry air" that's been more or less purged of water vapor.

The most sensible thing to do is get a tire pressure gauge and check the pressure regularly.

 

[bcla]

but this also means that people who live in areas that don't have drastic shifts in temperature don't see as much benefit from Nitrogen in their tires.

The temperature in my part of the world is up and down like a toilet seat this time of the year (Can drop 20 degrees in one day), and it can cause issues. I use regular old air in both my vehicles, but that's more because I'm cheap, than whether it's effective or not.

But your mechanic has given bad advice, you shouldn't over-inflate your tires, this can cause handling issues with your vehicle.

Actually - temperature shifts don't really affect nitrogen any better or worse than air - especially dry air that's been purged of water vapor. All gases follow the ideal gas law except to some minor effect unless it condenses to liquid/solid. Also - water vapor barely has an effect on the pressure of a tire. It's probably not even measurable within the 0.5 PSI tolerance of most pressure gauges.

http://en.wikipedia.org/wiki/Ideal_gas_law

This is pretty close to what you'd see in a tire. The temps will never get cold enough for there to be a dramatic difference in pressure between ordinary air and nitrogen. The ideal gas law breaks down in certain extreme conditions, but not in any conditions where a human being could survive.

 

[Gumbo4x4]

Not really. The pressure difference between the 98% nitrogen and a typical air mixture (especially dry air) will be virtually linear with any kind of reasonable temperature. The only possible difference is that the input from water vapor will go to zero once it turns to liquid and/or ice. The amount of water vapor isn't going to cause a dramatic loss in pressure.

The ideal gas law is PV = nRT - or pressure * volume = amount of gas * universal gas constant * absolute temperature. Unless it's getting so cold that this gas is turning to liquid (or solid) it's not going to cause anything dramatic to happen.

The main benefit of generated nitrogen may be that it's relatively free of moisture. However, it's possible to get "dry air" that's been more or less purged of water vapor.

The most sensible thing to do is get a tire pressure gauge and check the pressure regularly.

But you're no typically going to get "dry air", especially in places of high humidity.

 

[Squirlz]

Cold most certainly does reduce air pressure. Take a sealed empty 2 liter pop bottle. Put it out in the cold and see what happens

I would never pay for nitrogen. I think they are just fleecing NASCAR fans

 

[Farps]

I had nitrogen in all of my tires when I bought my new vehicle a few years ago, and the pressure barely fluctuated in the tires from summer to winter. When I had to purchase new tire they did not put in nitrogen so now I need to add air quite a bit more when the temp drops. That being said I definitely think that with nitrogen filled tires the pressure does not fluctuate as much.

 

[bcla]

Cold most certainly does reduce air pressure. Take a sealed empty 2 liter pop bottle. Put it out in the cold and see what happens

I would never pay for nitrogen. I think they are just fleecing NASCAR fans

Of course it does. Driving on the freeway heats up tires enough that there will be a pressure increase of a few PSI.

However, the difference between nitrogen and just air is minimal. They'll change in pressure with temperature the same to any meaningful amount around where we're likely to drive. It certainly doesn't produce the purported fuel economy, reduced wear, or longer tire life that is claimed by those wanting people to pay $10 a tire to inflate with generated nitrogen. You simply can't get around the fact that regular air (about 20% oxygen, 80% nitrogen, and small amounts of other gases) and generated nitrogen operate pretty much according to the ideal gas law.

There might be some reduced leakage, but nitrogen still leaks. If you regularly check your tires, regular air is fine and you don't have to worry about topping off. Also - many places will charge to top off with nitrogen.

 

[manning]

Air pressure decreases with colder air. The advantage of nitrogen vs "air" is that this effect is much less dramatic with nitrogen.

The idea behind this is that nitrogen molecules are larger than air molecules and suppose to stop leakage.

 

[tvguy]

DH says the mechanic recommends 35 psi and wants DS to go have more nitrogen put in them because he says every time it gets cold now the light will come on. .

The Michelin dealer I go to says the failure rate of those low pressure sensors is about 100% after 3 years no matter what you put in your tires. They stopped carrying nitrogen.

 

[bcla]

The idea behind this is that nitrogen molecules are larger than air molecules and suppose to stop leakage.

I didn't think that's what was being discussed. I thought the claim is that the amount of pressure decrease from a colder ambient temp is lower with nitrogen. The pressure decrease is linear with absolute temperature regardless of the composition of gas.

Now "size" is really tricky when talking about gas molecules. There's no real physical size to a gas molecule, although I'm not really all that well versed on quantum mechanics. There are some numbers thrown around, but they're kind of oddball since gas molecules aren't exactly hard spheres - more like balls that can deform and "squish". At those sizes, it's kind of an approximation based on experimental data. I have heard of crazy stuff like bike tires inflated with helium, which apparently will leak like crazy.