Driving on Nitrogen-Pumped Tires

[snopes]

Nitrogen is a gas that some automotive-service outlets and parts suppliers are promoting as a superior alternative to common compressed air typically used to inflate tires.

http://online.wsj.com/article/SB119327758675270816.html

[Mycroft]

Nitrogen is better-suited to use in tires than compressed air in part because its larger molecules don't seep or "migrate" through the tire's rubber skin as quickly.

The three main components of dry air are Nitrogen, Oxygen and Argon, of which Nitrogen has the smllest molecules.

[Troberg]

Nitrogen is better-suited to use in tires than compressed air in part because its larger molecules don't seep or "migrate" through the tire's rubber skin as quickly.

Yep, and practically all of the leakage happens between the rim and the tire when hitting potholes or curbs.

The only reason I could possible think of is that nitrogen would slow down the aging of the rubber, but even that is far fetched, as I've yet to throw out a tire because it gets old on the inside first...

Just a clever marketing scam, imho.

I work at an auto dealer. The owner of my company wanted to test Nitro Fill. We filled two of his tires with Nitro and the other two with normal compressed air. After 6 months there was no appreciable difference inthe pressure loss. We checked the pressures once a month and did our best to keep this as a real world experiment. Nascar, the airline industry and NASA all make use of nitrogen in their tires mainly due to the fact that pure nitorgen has a more predictable expansion and contraction rate which is helpful for aircraft and spacecraft which handle extreme temperature and pressure changes due to altitude changes. Nascar uses it since their tires handle massive pressure and temp changes due to the very high speeds they travel.

Just my two cents worth....

[Hero_Mike]

There is, actually, a good argument for nitrogen-filled tires. The "air" from the compressor at your garage will probably contain both moisture (as the moisture traps are not all that good), and oil (because they are used for air tools). Neither of these things are good, but it's especially the moisture in the air that can cause problems if you live somewhere where the temperature drops below freezing. Moisture in the air inside a tire can accumulate and re-freeze, or more importantly, cause your rims to corrode.

It may not be worth the extra expense, but there is a marginal benefit to "dry" air in your tires.

[KirkMcD]

Car Talk's Tom and Ray's Take on it:
http://www.cartalk.com/content/colum...bruary/02.html

TOM: And finally, both the oxygen and the small percentage of moisture in the atmospheric air can contribute to degradation of the inside of your tires and wheels. But think about it: The outsides are exposed to the air all the time, so what are you worried about the insides for?

[Roadsterboy]

Originally Posted by bear68

Nascar, the airline industry and NASA all make use of nitrogen in their tires mainly due to the fact that pure nitorgen has a more predictable expansion and contraction rate which is helpful for aircraft and spacecraft which handle extreme temperature and pressure changes due to altitude changes. Nascar uses it since their tires handle massive pressure and temp changes due to the very high speeds they travel.

Formula One and, I believe, Champ Cars also use nitrogen for tires, for exactly the same reason you state. I think the "dryness" helps in this instance as well, as the less moisture in whatever's in the tire (herewith called "air"), the less expansion and increase in pressure (I think. Feel free to correct me if wrong).

-D.

Originally Posted by bear68

the fact that pure nitorgen has a more predictable expansion and contraction rate

Basic physics of gases states that the volume pressure and temperature of gases is determinted by the equation: PV = nRT, where

P = Pressure
V = Volume
n = number of moles of gas (moles is a certain number fo molecules)
R = Universal Gas Constant (same for all gases)
T = Temperature (on an absolute scale such as Kelvin)

n does not change for gas in a closed system (such as a tire with no leaks) and R does not change at at (it is a universal constant)

So, for any closed system, the amount a gas expands or contracts (i.e., the volume) is directly variable with temperature and inversely variable with pressure. It doesn't matter whether you have air, pure oxygen, pure nitrogen or poo gas. If you have a fixed amount in a closed vessel, the volume changes by exactly the same amount.

The only reasonable explanation I've seen as a nitrogen benefit is that it doesn't leak as readily. But as was pointed out above, it occurs in smaller molecules than oxygen, the next most likely element in air, so it's hard to see how that is a benefit. There is a very small weight benefit since N weighs less than air, and in the microscopic margins of airline profits and space travel economies, it makes some sense to use it, but on a car I can think of no reason why nitrogen is better than air.

[A Turtle Named Mack]

Originally Posted by Mycroft

The three main components of dry air are Nitrogen, Oxygen and Argon, of which Nitrogen has the smllest molecules.

Quibble: Argon does not form molecule, being an inert gas. However having the same number of shells as nitrogen, but more protons, its electron are more tightly bound and hence have a slightly smaller outer orbital. As for oxygen, the molecule might be a tiny bit smaller, but the more important fact for leakage is that both nitrogen and oxygen molecules are essentially tiny rods, so that they have to strike end-on at just the right place to leak through.

But basically the leakage claim is just stupid.

[Wolf333]

Nitrogen is used in aircraft tires because it does not expand or contract to the same extent as common air. Until we began using nitrogen, there was a waiting period before tire pressure checks could be accomplished (4 hours) due to the tires still being heated from the landing, which would cause the tire to seem over-inflated (or under-inflated tires would read normal). Also, in very cold conditions, tires could easily be over-inflated.

With nitrogen, the tire pressure will remain within 1 or 2 psi within a very wide temperature range.

Consumer Guide did a test on this. They left one tire inflated for a year with air, and one with Nitrogen. The tire filled with air had leaked out about 4psi, and the Nitrogen tire leaked out about 2psi. Not much of a difference, especially for a year's span of time.

[Troberg]

Nitrogen is used in aircraft tires because it does not expand or contract to the same extent as common air.

Aircraft tires also work under much tougher conditions. They are slammed down while cold with 50 tons above them into a runway at several hundred km/h. Nowadays, they are spun up to speed before landing, but on older aircraft, they had to perform this feat from standstill. It's no wonder they have a need for more advanced solutions.

[Richard W]

Originally Posted by Doohickie

So, for any closed system, the amount a gas expands or contracts (i.e., the volume) is directly variable with temperature and inversely variable with pressure. It doesn't matter whether you have air, pure oxygen, pure nitrogen or poo gas. If you have a fixed amount in a closed vessel, the volume changes by exactly the same amount.

This isn't quite true - the Ideal Gas Law is an approximation that assumes you have an "ideal gas" where all the molecules are point masses. In reality, and especially under pressure, the size of the molecules does have an effect, and so it's not unreasonable that it might be easier to deal with molecules that are all the same rather than a mixture. The approximation assumes monatomic molecules, which is true for nitrogen but not oxygen. Nitrogen also has the smallest molecules, as mentioned above, so of the components of air, it will be the one that behaves closest to an ideal gas.

I don't know whether that makes an appreciable difference in practice or whether the motor racing teams are just imagining it, but they do tend to measure performance pretty accurately and milliseconds make a difference to them, so I'm guessing it will be a real effect.

[A Turtle Named Mack]

Originally Posted by Richard W

The approximation assumes monatomic molecules, which is true for nitrogen but not oxygen

This thread inspires quibbling so here goes: Nitrogen is virtually never found monatomic. In the atmosphere in particular it is almost entirely in the form of N-N triple-bond molecules. I would think actually that in monatomic form, it would be light enough to bleed into space as argon does (but is continually replaced by uranium decay). Probably some does escape anyway, butnot near so much as it would.

[snopes]

Q: What are the pros and cons of using nitrogen in tires? I have a brochure from my local dealer which I received when I put the nitrogen in my tires. The brochure indicates increased tire service and better gas mileage. I am not challenging the accuracy of the brochure; however, I will appreciate your thinking on the use of nitrogen in automobile tires.

http://online.wsj.com/article/SB1000...060905304.html

Nitrogen is simply air with the oxygen and water vapor removed.

Oxygen is a problem since it is under pressure and reactive - it can cause steel wheel rims to rust, which removes gaseous oxygen and hence lowers the pressure. It also isn't good for the rims. If you have steel wheels make sure the paint is intact on the interior, if you have alloy wheels this isn't a concern. Oxygen will also oxidise the tire rubber which isn't good - but I think this is a minor concern.

Water vapor is a problem since it can condense at low temperatures, causing larger pressure changes with temperature changes than dry air or nitrogen.

Nitrogen permeates though rubber approximately 3 times more rapidly than oxygen. (Graham's Law not withstanding - it doesn't apply to permeation.) But my experience is that permeation happens so slowly that is isn't a big concern.

My opinion is that if nitrogen is available for free or a reasonable cost when you install a tire, then go for it, but don't worry if you have to top it up with compressed air. I wouldn't pay $10 per tire, that's extortion. $1 maybe.

It's much more important to make sure your tires are properly inflated than to worry about what they are inflated with.

My mechanic recently began injecting some nitrogen into my tires, because the oxygen combined with the wet climate of the northwest had created quite a bit of rust and the wheels had actually been at risk of getting stuck in an emergency situation. I wish it didn't get to this point, but so far so good.

[snakeseare]

Originally Posted by RumorMilling

the wheels had actually been at risk of getting stuck in an emergency situation.

That makes absolutely no sense at all. If your mechanic is charging you for nitrogen, he is ripping you off.

Race teams use nitrogen because there is no water in it. Water can condense or boil, causing changes in tire pressure. Race teams measure tire pressure to 1/4 psi, so small changes from water are undesirable.

But for passenger cars, nitrogen is useless. All those claims are outright lies to steal your money.

Besides, how much water is there really in regular compressed air?

Personally I'd be more worried about the corrosion from the outside.

[RichardM]

Yes, wheels can rust in place causing great difficulty in getting them off. BTDT. But no matter what gas is inside the tire, it will not affect this rusting in any way, shape or form. The gas is inside the tire. The rusting occurs on the outside of the wheel.