re: Nitrogen filled tires- Does it help with pressure loss in changing temperatures

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The Truths and Myths of nitrogen

Lately there seems to be more and more hype about nitrogen gas for tires offered by tire companies and nitrogen services. Some services will "purge" your tires of air and replace it with near pure nitrogen for $20 per tire. Some tire shops are charging as much as $5 -10 per tire to fill them with nitrogen claiming everything from improved fuel mileage to a more comfortable ride. Is there any truth to this? Here we will take a close look at some facts and let you make up your own mind. At the bottom we show the results of our real-world gas comparison test that you might find interesting. In this article we refer to "gas" which includes air, nitrogen, and CO2.

Claim #1. "N2 doesn't expand with heat like air because it's drier so your tire pressures stay more constant through tire temperature changes." Here's a claim that we've heard more times than we';d like to admit. Bottled nitrogen is dry, drier than typical air, and it is said that a drier gas will exhibit less pressure change to temperature changes. This would mean that as my N2 filled tires heat up, the pressure will not go up as much as if they were filled with air. The dryness of CO2 is also put into question since it is a "liquid" gas under pressure. CO2 vapor is very dry. Don't forget that N2 is also a liquid gas under certain pressure and temperature. The truth is, the differences in thermal expansion values (TEV) between N2, air, and CO2 at automotive tire pressures is virtually undetectable to a driver. In our own tests we compared the pressure changes of N2, air, and CO2 through a wide temperature range and found that they all expanded (increased in pressure) at virtually the same rate (see Gas Test).

Claim #2. "N2 permeates (leaks) through tires slower than air therefore your tires will maintain their pressure longer and require less maintenance."
Although it is true that nitrogen does permeate through tire rubber slower than oxygen and CO2, there are two things to know. First, the gas permeation difference between oxygen, CO2 and nitrogen through a tire wall is very minute. Second, this difference is made even more insignificant for N2 since oxygen only makes up 17% of air and most of "air" (78%) is nitrogen. Diffusion speed through the walls of your tires has more to do with the quality, the wall thickness, and the age of your tires. More often, tire deflation is due to a leak in the stem core, the stem seal, cracks in the stem, a bad tire to wheel bead seal, cracks in the tire wall, or objects like nails stuck through the tire tread. Also, did you know that your tires may grow during the first 1-2 days as it gets used to being inflated which would reduce the tire pressure. Tire manufacturers recommend checking your tire pressures often no matter what type of gas you';re using to fill your tires. Bottom line: If gas permeation was the only way a tire would lose its "air" there would be very little detectable difference between air (which is already 80% nitrogen), nitrogen, and CO2.

Claim #3. "N2 is safer because it is non-combustible and therefore less likely that your tires will catch on fire."
This is true and is one reason aircraft tires are filled with nitrogen. But when was the last time your tires had to skid on pavement from 150 mph carrying 75 tons of vehicle, passenger and cargo weight? The chances are your tire is not going to burst into flames because of the additional 17% oxygen content inside your tires especially since your tires are surrounded by air anyway. If you have ever seen a tire smoking on the freeway chances are the tire was overheating from under-inflation. Putting nitrogen inside your tire will not prevent a tire from overheating. "But didn't I read that nitrogen will make my tires run cooler?" This statement is false. N2 cannot dissipate heat from a tire any faster than air or CO2 nor can it decrease heat producing friction between your tire tread and the road.


Claim #4. "N2 is safer for my tires because air contains oxygen and oxygen corrodes the inside of my tires."
Although it is true that oxygen permeating through the tire';s carcass may cause a certain level of oxidation, tire failures are typically not due to corrosion from the air inside. Don't forget, the outside of a tire is also exposed to oxygen not to mention harmful UV rays and ozone, the occasional curb bump, random road hazards, road salt and even dog urine. In fact, the leading cause of premature tire failure is tread separation caused by overheating; the overheating caused by friction from insufficient tire pressure. Premature tire failure is typically not caused by tire deterioration from the inside. CO2 vapor is dry and inert and also poses no corrosion issues to your tires. There is, however, one other possible cause for corrosion of tires that sit for long periods and that is moisture permeation from the ground. It is recommended that a moisture barrier (plastic sheet) be placed beneath each tire before long term outdoor storing.

Claim #5. "N2 is inert and therefore will not corrode the inside of my metal wheels."
This is TRUE, but who cares? Air won't corrode your wheels to the point of failure either, neither will CO2. Metal wheels Don't commonly fail due to corrosion from the inside of the rim. Wheels are well engineered parts of your car and for good reason. They support tons of moving weight over uneven terrain and obstacles. Have you ever heard of swapping out old wheels for new ones because the rims were made unsafe due to corrosion?

Claim #6. N2 in tires provides a smoother ride.
Yes, this is an actual claim in a nitrogen supplier's literature. Since nitrogen is no "softer" than air or CO2 our assumption for the claim is that if the nitrogen pressure doesn't increase as much as air the tires stay softer as the tire heats up. This is false (see Gas Test).

Claim #7. "N2 is used in aircraft tires and the NASA space shuttle tires so it must have advantages for me too."
Aircraft tire manuals state that oxygen content in the tires must not exceed 5%. This is to minimize combustibility. These tires also see extreme temperature and altitude swings that your car or RV tire will never experience.

Claim #8. "N2 in my tires will save me in fuel costs."
Fuel savings from tires depends on tire pressures. As long as tires are kept up to their proper pressures it does not matter which "gas" is in them. And no matter which gas you choose you should keep up a regular and frequent tire pressure check procedure because you never know when you may have picked up a nail or other tire damage that could be causing a leak.

Claim #9. N2 will make my tires last longer.
Tread longevity depends on tire pressure maintenance, alignment, and a properly working steering and suspension system. The only difference N2 makes in the interior of the tire is that there is no oxygen being diffused into the tire';s rubber. Interior carcass deterioration from an air filled tire is not an issue to be concerned about especially when compared to the affects of heat, UV, moisture, ozone, and road hazards that the tires are constantly exposed to.

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