A local dealership has ads now saying that for $40 they'll fill your tires with nitrogen leading to better tire wear, gas mileage. The leadin is to attract people whose tire pressure monitors are going off, they say they'll fix that too.
Has anyone ever heard of inflating tires with nitrogen? I'm having trouble figuring that out. Maybe some of our more scientific minds can comment.

 

we just had this talk yesterday in another thread. Costco charges $40 to mount and balance tires and uses nitrogen (free refills). Maybe see if you can go by and get them to do it.

makes no difference, but if it's free, why not? spending $40 =

 

Ha its a scam, $40 dollars for something thats all aorund you, not worth the money, take that 40 dollars and fill up the tank and go run the backroads!

Jack

 

PGT costco only charges 40 dollars to mount and balance? Do you have to buy the tires etc. from them?

Jack

 

Yeah, come to think of it the air we breath is about 20% oxygen and 80% nitrogen (+/- hydrocarbons). Sounds like mumbo jumbo to me. Now how about helium? That might be interesting!

 

air is 80% nitrogen!! It can't make that much difference. There is little to no difference in heat capacity between pure nitrogen and air. I think its a waste of money. The only difference would be that nitrogen can't react with substances and form oxides, but tires are not that reactive with 02 anyway.

 

The main advantage is the fact that the nitrogen has been completely
dehumidified. The water vapor in the air we breath makes for more of a
pressure gain as tires warm up.

 

my local one mounted tires for me that I brought from Tire Rack. Stock size on stock wheels. No guarantees at other locations with non-stock sizes though.

 

which why this was considered and old racer's trick...

 

Not sure this is worth paying for or true at car tire pressures. All gas pressure responds to temperature increases at constant volume the same way, P=nRT/V. As long as there is not liquid water in your tires this effect is going to be unmeasurable. In fact one could argue that the water vapor, having a higher heat capacity than nitrogen or oxygen could keep the tire cooler and the pressure lower. Moral to the story, nitrogen filled tires is a gimmick, don't pay for it.

 

Yet another example of someone using scientific sounding claims to separate people from their money. And since most people have little to no science knowledge, it works!

- I agree with glangford. Under the same conditions, the tire will have the same number of gas molecules, regardless of the contents of the gas. This is first-year chemistry.
- I don't see why water molecules, as opposed to nitrogen, will cause more pressure gain as you drive.
- The nitrogen molecule, N2, while lighter than oxygen, O2, _is_ a bit larger in volume than oxygen, so nitrogen will escape at a slower rate, but air is largely nitrogen. I suspect that overall impact to be negligible.
- I also don't see any material harm from a small amount of water vapor in the tire. Is it to protect the tire? What about the water in the air around us?

Best way to care for your tires is to check the pressure every week or two.

- James (yes I do have a degree in chemistry ...)

 

Now THATS's what I was hoping for, a chem grad! Thanks.

 

Several years ago, Shell stations down here changed out their air pumps to supply nitrogen, the idea being that it leaked out more slowly due to the increased size of the molecule and that a more stable tire pressure would lead to a safer car. The program quietly went away when nobody would pay the extra for nitrogen. But they sure didn't charge $40.

 

Nitrogen is sometimes used in tires for motorsport. It is more stable in regards to expansion or contraction in temperature changes. Worth $40? No... if your tire light goes off, just refill it with free air.

 

Is there any difference in the expansion with temperature between water and nitrogen?

I've read reports of people removing an old tire to find water that had condensed from the air pumped into over time. Or, discovering that the high-speed vibration was water in the tire, rather than it being out of balance. I don't know if that is true, or urban legend. If you've ever owned a compressor, you've had to drain the tank periodically to drain out the water. The compressors is dealing a with a much greater volume of air going through it, and higher pressure. So, I don't know how it would work with tires.

I had nitrogen put in my tires when I had them mounted. However, it only cost a few $ per wheel. I was told that it would not leak as fast, was dry, would and eliminate oxidation of the rubber from the inside. However, they weren't claiming these were major improvements. I thought it was kind of cool so paid the few $$. I wouldn't pay $40.

 

Well, I have first hand experience in filling tires with nitrogen with pleasing success and I do not view it as a scam, but then again, I do it myself because I own my own nitrogen purging system and I rent nitrogen tanks from my gas supplier.

My experience is more even tire wear due to less pressure variances. Better gas mileage, although this is hard to measure, more constant pressure. I have had my tires filled with nitrogen on another vehicle for 2 years and have only had to adjust pressure due to loss once in that time, at about midway (1yr. mark), this is with driving 16-20k miles per year.

I also have my spare tires filled with nitrogen with little to no pressure loss in the same amount of time.

I have another vehicle in storage resting on its tires in a non-climate controlled facility on concrete and have had no pressure loss in over 2 years, not driving on them, just starting to keep engine in working order and maybe driving 5 miles or less per 6 months.

In colder climates, it is more important to have your tires filled with nitrogen due to pressure variances/loss.


Read this article and judge for yourself. BTW, I only charge $35 for the first fill and $10 for total top-offs. The fee covers my cost for the equipment and the labor to get the wheels off the ground during the one time purging.

http://www.tommcmahon.net/2004/11/fill_your_tires.html

 

Ha, another one, I'm chem grad as well. To answer Robin's question, there should be no difference in expansibility of the different gases. 1/V(DV/DT). In essence what James and I are saying is that at normal pressures of a tire the gas behaves ideally (i.e. the individual molecules (of different composition) act and respond the same to changes in pressure, temperature, volume, etc.) Only at very high pressures (hundreds if not thousands of psi) does this break down and intermolecular forces cause some departure from that 'ideal' behavior. Liquid (non gaseous) water in your tire is something else and potentially could be a problem particularly in amounts that could cause it to seem out of balance. (although at high speed I'd expect centrifigal force to just flatten it all out along the outside diameter of the tire inside. I doubt seriously it would be much of a pressure problem, the pressure increase could be no larger than the vapor pressure of water at the temperature of the tire, if you had enough liquid to even do that. The one exception would be real high performance race tires, like formula 1 or NASCAR, where small pressure increases (a psi or two) can make the difference in how the car behaves at 200+ mph having extremely high tire temperatures. Not sure I buy the leakage theory. O2 and N2 are so similar in size and shape and 99% the composition of air, I'd doubt there would be any difference in leak rate of the two gases in a tire. The atmosphere does contain about 0.5% argon, that would probably leak out before 02 and N2.

 

I followed the link, http://www.tommcmahon.net/2004/11/fill_your_tires.html, but these are just personal testimonials -- anecdotal evidence. No information here, just people who want to rationalize their purchase, or sell you a product.

Nitrogen certainly does no harm and if it makes you feel good, do it. But I can see no reason to spend money for a higher percentage of nitrogen.

 

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Agree with the snake oil assessment.

 

I got it done at a Honda Dealership nearby my house. It was 20 bucks there. Plus free refills.

 

Well, we are all entitled to our opinions, but I do not feel I had to rationalize anything, I just compared the performance in high end sport tires with air and then nitrogen and was happy with the findings, all from personal experience.

Much less maintenance. And if it proved to me not to make any difference in life of tire or performance or increased mpg, the cost of the purging system or the gas was no biggie at least to me.

Fortunately, this has not been the case in 4 of the vehicles, plus a utility trailer, that I own,

There are critics out there and I respect their opinion as I was one of them prior to purchasing the system, but I wanted to see for myself, so I bought my own system (since no one in my area (100 mile radius) performed the service), started noting air runs vs. nitrogen runs, and well, I have already stated the rest. I am happy with my decision.

 

Agree with water vapor acting approximately as nitrogen, oxygen, or
the hypothetical ideal gas, but what about the phase transition between
liquid water and water vapor. As the tire heats up, more goes into vapor,
and when it cools down, some condenses, which would act similar to
adding air when the tire is hot and removing it when it's cold.

Not sure if enough of this happens to make a measurable difference, but
could probably be calculated. If I have time I'll try to make an estimate,
but I'm not with my old physics and chemistry books right now.

 

why don't we just steal some documents from ferrari and settle this once and for all....

 

so a couple things....

If you autocross or run track days, you'll know that your tires will gain about 5 - 7 psi during a run. And that is working the tires very, very hard. During normal street driving, the tires are not heated nearly as much.

nitrogen is like any gas and will still expand at a similar rate to 'normal' air, which is mostly nitrogen anyway.

the only benefit I can possibly see to using nitrogen is that it is dry, but then air from a good source should be dry as well.

regarding the nitrogen molecule not leaking because it is bigger: if that is the case, then when you fill up with normal air, and have some gradual pressure loss, it should be only the oxygen molecules escaping, right? so adding more normal air (mostly nitrogen) over time would gradually increase the % of nitrogen in your tires, until eventually you'd have tires filled with nitrogen anyway, for free!

personally, I have better things to spend my money on. like yesterday, I saw an ad for something called a 'turbonator'.....

 

Let's say there's about 22 liters of airspace in a MINI tire (1 mole of air).
If you fill the tire on a rainy day at 30C, the air's about 3% saturated
with water vapor. At this point, unless there's some water condensed
in the tire already, it won't go up further with higher temps, but if the
temp goes down to 0C, the amount of water vapor in the air goes down
to about 0.7%. I haven't done a rigorous analysis, but this would make
the tire pressure go down about 1psi from say 33 to 32 in addition to the
decrease of the pressure from cooling the air in the tire (another 3 psi).
In this case the tire would go from 29 psi at 0C to 33 psi at 30C with air,
and from 30 psi at 0C to 33 psi at 30C with nitrogen (or dry air).

If there were actually several grams of water sitting in the tire at 30C,
(say you keep adding air to tires on hot humid days, some could accumulate)
then there could be a significant increase in pressure at higher temps (several psi)
beyond what one sees for simply heating up the air in the tire.
On the track, one can easily see tires heat up to 70-80C).

Having said all that, I don't use 100% nitrogen in my tires,
just regular air from a high volume bicycle pump.