Nitrogen Instead of Air in Tires

[YBLee]

A local TV station (from Boston) ran a story tonight about the use of Nitrogen in tires to help with gas milage and also prolong tire life. I searched this sight for threads on "Nitrogen" and only found one from 2004. Is this topic gaining legs again and is there anything to it?

[skruse]

Two gases make up 99% of Earth's atmosphere: Nitrogen and Oxygen. Atmospheric composition is relatively stable up to about 80 kilometers above the surface. The remaining 1% is mostly inert Argon (0.93%) plus tiny quantities of other trace gases. Carbon dioxide is present only in small amounts (0.039%). Variable components include water vapor, particulate matter and ozone. Nitrogen is unreactive at normal temperatures.

Filling automobile tires with Nitrogen may make you feel emotionally better, but does nothing for the tires.

Atmospheric composition:

Nitrogen 78.08%
Oxygen 20.94%
CO2 0.03%
Argon 0.093%
Neon 0.0018%
Helium 0.0005%
Krypton trace
Xenon trace
Ozone 0.00006%
Hydrogen 0.00005%

[aaf709]

Using nitrogen is supposed to help prevent leaking due to the molecule size (so I hear), plus it's not supposed to heat up as quickly in the tire as regular air. Costco will fill your tires with nitrogen, but IIRC it's $10 per tire.

FWIW, it's not something that's on my "gotta do" list of things to change on my Prius.

[auricchio]

Inflating tires to the correct pressure will do far more to improve MPG and tire life than using nitrogen. Forget the silliness of whether nitrogen will help. Inflate the damn tires properly!

[YBLee]

So the fact that Nitrogen is used in Race cars and Aircraft tires would have no benefit to the Hybrid driver? If the Nitrogen molecule is larger and the air is dryer and therefore there is less variation in "running temperature" tire pressure, why wouldn't there be a positive benefit to using it that might cost-justify the expense? There 's really only one way to get to the bottom of this for sure and that is a DOE, Design Of Experiemnts. I believe: "In God we trust", "Everyone else bring data"!

[mssmith95]

Yes, Costco is the one for that.

If you buy tires there (they can get just about any tire), they fill them for free...and continue to do so as many times as you like.

I disagree with the statement that just filling the tires to the correct pressure is better then Nitrogen, as Nitrogen is much more stable and the tire pressure does not have the significant fluctuations as it does with standard air. This would seem to lead to getting both a more consistent ride...and more consistent MPG.

The only problem is that it is a pain to only be able to go to Costco for it...so chances are until I have to get new tires, this is something that is too much trouble for too little gain.

[jbarnhart]

This is the best post I found on the subject, and it sums up my opinion. I found it in the thread linked here.

The question about nitrogen in tires has come up in other lists on the web as well. Let me clarrify a few points.

1. Air is 78% nitrogen, N2, and 21% oxygen, O2. So even if you put air in the tire, it's already 78% nitrogen. Many of the so called nitrogen generators don't produce much more than 90% nitrogen.

2. At relatively low pressures (ie tire pressures) N2, O2 and water vapor will all behave as ideal gases, and follow PV=nRT. Pressure will increase or decrease to the same extent as the temperature increases or decreases regardless of which gas is in the tire. (Even at 300 psi, which is about 20 atm, there is little deviation from ideality.) Therefore the comments about N2 not changing in pressure as the temperature changes are without merit.

3. The rate of effusion (or diffusion) of a gas through a porous membrane depends on the molar mass and to some degree on the molecular diameter. N2 and O2 are almost the same size and N2 is lighter than O2 (28 g/mol vs 32 g/mol) so if either gas were to effuse out of the tire, nitrogen would do it more quickly. Luckily, tires are designed not to be porous membranes.

4. N2 and O2 both have essentially the same specific heat capacity, about 1.0 J/gK, and thermal conductivity, about 0.00026 W/cmK. Water vapor has a specific heat capacity of about 2 J/gK. But remember, water vapor will constitute less than 1% of the air in the tire. So the idea that N2 has different heat handling properties is also without merit.

5. The ozone, O3, in the atmosphere, which is a ground level pollutant, will do a great deal more damage to your tires than the O2 inside the tire. For instance, don't leave a condom out in the air in Los Angeles for a few days. It will develop lots of tiny holes and weaken.

spdracer22 says that dry air is preferably to air with a lot of water vapor. As a tire heats up, the very small amount of H2O present will be in the vapor state which may contribute to the overall pressure very slightly.

Several have suggested that N2 in a high pressure tank is more portable and requires no electricity. That would make sense, particularly for aircraft tires.

I find no reason to believe that N2 is going to produce a "better ride" or "better handling".

The bottom line is that for general passenger car tires or truck tires there is nothing to be gained (other than portability) by using nitrogen rather than air. The biggest gain will be $$$ by the companies that sell nitrogen handling equipment and the tire merchants that appeal to ignorant customers. And who is the biggest loser? Yep, the consumer.
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[Scott_W]

As I see it the one BIG problem with filling your tires with nitrogen is that if you're being chased by bad guys and end up going in the water, you won't be able to out-smart SPECTA like James Bond did in that movie.

[qbee42]

One advantage to N2 in aircraft tires is that Nitrogen will not support fire, which is a risk at the speeds used for landing. This is also true of race cars, which are in much greater danger of setting tires on fire - kind of hard to do in a Prius with traction control.

I suppose much of the interest in using Nitrogen in tires comes from the use of dry Nitrogen in optics and other devices where water vapor will condense and cause fogging. We consumers tend to make funny leaps of logic: if it's good in telescopes, it must be good in tires.

Tom

[Tempus]

I always thought filling them with Helium would be best for mileage. :P