Why is nitrogen superior to air in tires?

Answer 1

The above answer is wrong. Nitrogen gas molecules are SMALLER than oxygen gas (nitrogen has an atomic weight of 7 while oxygen has an atomic weight of 8, both molecules are "diatomic" weighing in at 14 and 16 respectively). However, nitrogen gas behaves less like an "ideal" gas than oxygen does, so it packs together more in order to create the same total pressure. Nitrogen gas at the same temperature and pressure as oxygen actually weighs more by volume. Nitrogen gas is DENSER than oxygen gas. Proponents of nitrogen for tires will say that this translates to improved heat dissipation. If you're running 200 mph around an oval track or landing an airplane, this has meaning, otherwise its trivial.

Nitrogen gas is commercially isolated from air by cooling. At -183 C, oxygen precipitates out of air as a liquid. What remains is almost pure nitrogen. Of course, long before the cooling process gets that far down, any included water vapor has fallen out as ice crystals into a system of filters. Nitrogen gas is therefore quite dry. When gas is at increased pressures, the corrosive effect of moisture is accellerated. Nitrogen proponents for tires will say that this retards the process of corrosion on the exposed metal surfaces of the wheel rim.

Without additional oxygen in the gas, there will be significantly decreased oxidative potential inside the tire. Is the oxidative potential eliminated? No, it is not! There is 21% oxygen at 1 atmosphere of pressure inside the tire when you put the tire onto the rim. Unless you draw a vacuum inside the tire before you fill it with nitrogen, the oxygen will always be there! It will then be pressurized up with the rest of the gas mixture when the tire is filled.

Is nitrogen superior to air in tires? Perhaps in extreme situations like NASCAR or aircraft, yes. In everyday life? - certainly not! Have you ever heard of someone having to replace their tires due to internal oxidative damage? NO! When people replace their tires, it's because they've used up the tread life or have damaged the tire beyond repair. Have you ever heard of someone who has had to replace their rims because of rust damage inside the tire space? Personally, I have not heard of this, but I could conceive of it happening only in very vehicle abusive environments with high humidity and frequent filling of the tire with poorly filtered air. Perhaps mud boggers in the deep south have this problem. I don't know. I live in Arizona!

I drive a modified 4x4 with large tires. I drive difficult offroad trails and air my tires up and down frequently. I go through tires like a kid goes through bluejeans! I've never seen damage to the inside of the tire or rim from inflation using unfiltered air.

Some people use a product called "PowerTank" which is actually carbon dioxide. The advantage of CO2 is that you can crush a huge amount of it into a small tank. It's even LESS "ideal" than nitrogen! Commercially available CO2 is wet compared to compressed air. I've seen tires come off the rim on rigs using powertank frequently with beads of moisture inside. Still, no damage!

Like I said, I'm sure you can find people who will tell stories of rust damage due to moisture inside the tire, but for the average user (and quite a few extremists) not only is air just fine, but moist CO2 is just fine also!

EDIT - Mountain Crusher! Thank you !!! If I am remembering correctly, N2 is a diatomic molecule with a triple bond and O2 is a diatomic molecule with a double bond. Does the difference in bonding characteristics create a different molecular (long axis) radius?

Answer 2

I was told by the people when I had it done that the tyre rubber is more permeable to air than nitrogen, so the nitrogen tyres stay up for longer. No obvious reason to me as to why that should be, though. The components of air don't have that different relevant properties that I can see.

Edit having seen the answer above - yes, but nitrogen isn't a large molecule!

Answer 3

Don't waste your money. Maybe N2 gives a modicum of improvement over air, but you won't be able to tell the difference - except in your wallet!

EDIT - Belly Doc - Great answer, but I'm a chemist and I must disagree w/ only the size portion of your answer. Even though oxygen has a larger atomic mass, it does have a smaller atomic radius (65pm vs. 92pm) This is because atomic radius decreases across the periodic table. But you're right otherwise. Average users, and even above average users, will see virtually no benefit.

Edit #2 BellyDoc - Great point! I was focused on the single atom, not the diatomic form, which of course is how its found.

According to my CRC handbook, the bond length for O2 is 1.208A, and for N2, its 1.09A, so yes, the triple bond is smaller. However, the atomic radii change based on the charge of the atom, meaning that the radii I listed aren't directly applicable, since they were for single atoms, not the diatomic molecule. Also, I haven't been able to located the size of either N2 or O2. Bottom line, I can't say I'm right, and I can no longer say you're wrong.

Answer 4

Kerifitz is spot on.

I have a mate that owns and runs a large tyre garage and he said nitrogen is not affected by temperature. I've worked in the car industry and have always been told to avoid compressed air lines because the air is too cold and you can't get an accurate PSI reading. Always use a foot pump and an accurate gauge to get the exact pressure right.

Answer 5

By reducing the percentage of oxygen, water vapor and other gases in your tires from 22% to 7% or lower, your tires will maintain proper pressure longer than if you use “plain old air.” For example, with 95% nitrogen in your tires, they retain optimal pressure three to four times longer

Answer 6

The oxygen in the air may react with the rubber in the tires.
This would weaken the tires, and decrease the pressure in the tires at the same time.
Okay, I admit I'm guessing.

Answer 7

big molecules do not permeate the rubber so easily so the pressure does not leak away so quickly.


Air is more likely to corrode wheels especially in aircraft

Answer 8

Nitrogen is used in aircraft tires because it doesn't expand or contract with temperature variables

Answer 9

while fillingg air in petrol bunk we hav to say our tyre pressure? what does this mean in english?