does using nitrogen instead of air really work in tires? i have low profile tires on all my cars and i sometimes dont drive them months at a time so sometimes when i get to them the tires are low on air. thanks

 

I'd say the real advantage of using nitrogen is that it is dry, because it is purified, bottled gas that has no water vapor. If you used bottled air it would work just as well.

 

I reposted this last year. I hope you find it helpful:

First, the claim that pure N2 provides more "stable pressure" than air over a change in temperature. Not true. Here's why: as a consquence of Avogadro's law, The ideal gas constant has the same value for all gases. This means that the constant k = P*V/T
where:
P is the pressure of the gas, V is the volume and T is the temperature of the gas has the same value for all gases, independent of the size or mass of the gas molecules. In other words, it doesn't matter what the gas is, the pressure change is going to be the same for a given change in temperature.

So let's apply this to the real world. If you're at a track day, and your tire temperature goes from up from ambient, e.g. 20C to 100C, the pressure is going to go up by the ratio of absolute temperature, i.e. (100 + 273) / (20+273), or a factor of 1.27. So if you start at 30 psi, you're going to be at 38 psi. Might be time to take a break in the pits! This pressure rise is going to be the same whether you've got air, pure N2, or any gas you choose in your tires.

Ok, with that settled, let's look at the benefit in terms of how often you need to add air (or pure N2) to your tires. There actually is a small benefit here, but it's not as big as the nitrogen proponents would have you believe.

N2 and O2 have similar molecular weights, but it turns out that even though O2's weight is higher, it's actually a slightly smaller molecule. This has to do with electron orbits, van der Waals forces, and so on. There some other factors at play such that the permeability rate of O2 through rubber is actually quite a bit higher than N2, namely 10 for O2 vs. 3 for N2. This usually where the marketing scams start for the N2 guys, but let's take the next step.

Air is 78% N2 to begin with, so it's not going to leak out 10/3's faster. For pure N2 the rate is 3...how about for air? It's going to be .78*3 + .22*10 = 4.54. So, N2 will leak out more slowly than air, with a theoretical ratio of (3/4.54) or 0.66. Let's compare to the real world again. In a totally unbiased Consumer Reports article, they measured how much pressure a variety of tires lost over a year. Starting at 30 psi, the air filled tires lost 3.5 psi/year and the pure N2 tires lost 2.2 psi/year. How's this compare to the theory? 2.2/3.5 = .63, so both theory and empirical data are in good agreement here.

So, the ultimate question, is what's this worth to you? If losing 2.2 psi/year vs. 3.5 psi/year is worth $20 to $80 to you, go for it. If it's free, take it. I would submit, however, that you really ought to be checking the pressure in your tires more than once a year anyway with a high quality pressure gauge."

However, any claim that Nitrogen provides any handling benefit whatsoever, on the race track or anywhere else, is utter nonsense and totally unsupported by science. If you fill your tires with air, nitrogen, helium, or any other gas, it will expand EXACTLY the same when heated. It's called Avogadro's LAW for a reason.

Pyrokerry is correct that Nitrogen is 100% dry. But that simply minimizes the chance of corrosion over time.

It would seem the Nitrogen marketers have done an amazing job.
In my opinion, it is a complete waste of money and you'd be much better off donating to your favorite charity.

One of our comedic fellow 6Speeders chimed in last year that there is a weight savings, referring to the $80 missing from your wallet.

 

^ what a bunch of hot air....I mean nitrogen

good explanation Tech Mike

 

Tech 1_Mike

In your all knowing analysis you forgot to consider the change in pressure due to the partial pressure of the water vapor. Bottled nitrogen is a dry gas relative to compressed air. Very different in temp. response. Know what of you speak before you speak.

 

Thank you for the input. However, even from the Equatorial rain forest, the amount of water vapor in compressed air is no more than 1%. The nominal amount will be usually be .07%. Therefore, any change in pressure due to temperature will be negligible.
I stand by my post. If Nitrogen makes you happy, by all means use it. It just won't make the car or the tires perform better.

 

My dealer offered a free nitrogen fill prior to a day at the track. I had the same prssure increase after a track session that I normally experience with a regular air fill. So, empirically, I can say the nitrogen hype is hot air.

 

Thanks for the "real world" validation. The truth is, there can be no other outcome. This is science, pure and simple. There are absolute laws of physics at work here that no marketing hype can supplant.
I am simply amazed at how the Nitrogen marketers continue to claim almost everything in their advertising. At the recent SEMA show, I saw a Nitrogen marketer actually claiming a reduction in global warming-YIKES!
However, there is no negative in using Nitrogen, Helium or any other inert gas you like in your tires, save cost.

 

The best use for Nitrogen is in bottles to power air tools in a very damp environment like Miami...........your tools will last much longer. If you have to drain air compressors everyday you know about this. It's useless in car tires, unless it's free.

 

We do nitrogen in tires at work, i wanted to test them in real life to see. My corvette had sensors that showes each tire psi in real time in the dash. So for a week i wrote down the tire pressure changes from my garage at home to work. I started each day in my garage, so the temp is consistant and no sunlight on the tires affectign pressure.
For a week, the average startign ps1 was a consistant 33 psi cold leaving my garage. When i got to work 12 miles and 30 min later, average psi was 36 front and 37 rear. Averaged going up 3 psi frot and 4 rear.

This isnt beatin on it, just drivign to work.

Then to see the differnce i put notrogen in the front left and right rear tires, just to see if there was a difference, and there was, 2psi is all it would ever go up tops. So it is slightly different.
Ohh and 1% max water in the air? Really? Have you ever gotten air out of a compressor in south florida? It looks like an aresol when you spray from the tanks!

 

The typical 85-90% RELATIVE humidity in Florida means that there is about 4% water vapor in the air.
When air is compressed, it is heated (Boyles law, please look it up). The typical compressor raises the pressure by 8 to 10 bar (125-150 PSI).
When the compressed air cools, it can no longer hold the water in suspension, so the water condenses back to liquid. Most air compressor systems have traps and dryers to remove the moisture (not including the 25 cent ones at the gas station).

When the air is released from the compressor system it is cooled (also Boyles law). This is how your air conditioning system works. If there are residual drops of moisture in the system, they can be expelled, giving the impression of an "aerosol". However, the moisture content in the air can never be more than is was to begin with and it is usually far less, most often 1% or less. This is due to the condensation from the cooling gasses.
But even 4% water vapor, which is a GAS, will have a negligible effect on temperature rise when heated.
It is called Avogadro's law for a reason; it is a law of physics.

In closing, I would just like to say that the placebo effect of Nitrogen has been well documented in these forums.

 

Can't argue with you Mike, but do you know why so many crew chiefs in the Rolex, ALMS, and Indy car series ( I don't know about Nascar) are running nitrogen?

 

Your scientific data means nothing to me (NO OFFENSE).

I like Nitrogen better on the track because when I get a lot of heat in the tires they don't go up in pressure nearly as much as air.
In addition you don't loose pressure when ambient temps drop like you would with air.

 

It's called Avogadro's Law for a reason. It is a LAW of physics.
Your anecdotal experience is interesting to read, but without scientific foundation. (NO OFFENSE).
It is literally IMPOSSIBLE for nitrogen to expand at a different rate than compressed air when heated. All gases expand at exactly the same rate.
However, the placebo effect of Nitrogen is well documented in these forums.

Tejoe, teams use nitrogen because it is absolutely dry. Saves wear and tear on tools, equipment, etc.

 

T1M, you are ignorant. Stop spewing your half knowledge as if you actually know something. Take a chem 101 course to get a clue. You totally overlook the contribution to pressure change from the partial pressure from the water vapor in compressed air. Your knowledge is applicable only to dry gases. Pure N2 O2 CO2 all are the same as you state, however they contain NO WATER VAPOR. Pure dry gases present a consistent and predictable pressure gain where as with compressed air you have no consistent relationship due to the PP of water vapor. Just look at the vapor pressure tables to get a clue.