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Open Roads Forum  >  Class C Motorhomes

 > TIRES: Nitrogen fill worth it?

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wolfe10

Texas

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Posted: 06/06/12 03:53pm Link  |  Print  |  Notify Moderator

Sorry, with any gas (air or Nitrogen) you will still need to add some in winter and let some out for summer. Boyles Law DOES apply and PSI at 40 degrees F and 80 degrees F IS different.


Brett Wolfe
1997 Safari Sahara 3540
EX: 1993 Foretravel 36' U-240


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CapriRacer

Somewhere in the US

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Posted: 06/07/12 05:52am Link  |  Print  |  Notify Moderator

I know it is hard for non-technical folks to understand this whole business about the ideal gas law and leakage rates - and I know the "nitrogen lobby" has done a great job of disguising the truth, but it is the truth nevertheless. Nitrogen has little, if any, benefit.


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SprinterDriver

Kentucky

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Posted: 08/21/12 03:15pm Link  |  Print  |  Notify Moderator

I put 80,000 miles a year on my vehicle, and have so for the past 8 years. I have run two sets of tires without nitrogen and have gotten about 80,000 miles from each set. I've run 4 sets of tires with nitrogen, and have gotten more than 130,000 out of each set, and 20% better fuel mileage. I've used the same Michelin model of tire on every set. Real world results.

The moisture benefits of nitrogen are minimal unless your tires are on a plane at an altitude where water freezes. Nitrogen is a "slow" inert gas that doesn't react with anything, while oxygen is a "fast" gas which reacts quickly in the form of oxidation. It can cause rust around the tire seal bead and otherwise degrade a tire, but that can take many years. Regularly used tires will be replaced long before oxidation becomes much of a factor.

Despite the belief that nitrogen has little, if any, benefit, nitrogen absolutely leaks through the sidewalls of a tire slower than regular air does, so the pressure remains higher for longer periods of time. Instead of losing 1-3 psi per week as with air-filled tires, you lose 1-3 per month. That's really the primary benefit of nitrogen, it keeps your tires properly inflated for a longer period of time and across a wider range of operating temperatures, and properly inflated tires is one of the keys to tread wear and fuel economy. While air is indeed about 78% nitrogen already, the 21% oxygen is what makes the difference. Reduce the amount of oxygen and you reduce the amount that will quickly leak out. A "pure" nitrogen fill of between 93% and 95% is all it takes to make a dramatic difference in rate at which a tire loses pressure. Nitrogen above 95% offers no appreciable benefit.

The Ideal Gas Law that people like to bandy about is just that, an equation for a hypothetical ideal, or perfect gas, to give an approximation of gas properties. Nitrogen isn't an Ideal gas, it's a diatomic gas. And the Law has it's limitations, chiefly in that the Ideal Gas Law is only accurate at relatively low pressures and high temperatures. Tire pressures and temperatures (even in the summer at highway speeds) fall well out of the accurate range of the Ideal Gas Law as to be useful for any kind of accurate calculations.

I am often amused by the Green Eggs and Ham Sam I Am folks who have never used nitrogen and will make great efforts to justify their belief that nitrogen offers no benefits, even up to the point of using physics in junk science fashion (using certain laws while at the same time omitting important relevant variables). They also like to cite the Consumer Reports test that showed nitrogen leaked out of tires at a slower rate than regular air, but at only a modest difference. The problem with the Consumer Reports test was they simply filled the tires and stored them for a year without putting them on vehicles. Consumer Reports begrudgingly admits that installing the tires on vehicles and driving them may be a variable that was not taken into consideration (like the rapid heating and cooling and the resultant tire pressures associate with each which will cause increased permeability of the tires). The only benefit of the Consumer Reports study is when you are talking in the context of long term storage of tires. If you are anti-nitrogen, then please, by all means, don't use it. But there's no reason to try to convince others they are wasting their time and money for using it, simply to justify your own decision.

Properly inflated tires run cooler and will have reduced rolling resistance, both of which result in better tread wear and better fuel economy. Regular air will give you that, but only if you are vigilant about tire pressures. Nitrogen gives you that without you having to be anal about a tire gauge.

If your tires are filled with nitrogen and you need to have a tire repaired or add some pressure and there is no nitrogen immediately available, as strange as it may sound it's OK to add regular air to a tire that has nitrogen in it. You just won't get the benefits of nitrogen until you get that tire purged and refilled with nitrogen. No big deal. Just don't pay more than about $5 per tire for it. An 80 psi tire gets filled with about 50 cents worth of nitrogen, but the nitrogen generators are expensive and the time involved in purging and filling needs to be covered. More than $5 is out of line for anything other than large truck and motor home tires.

Those with passenger cars and light trucks who drive mostly locally and only put on 12,000 miles a year will see very little benefits from nitrogen, other than not having to add air to the tire as often. But those who do long trips and put a lot of miles on their vehicles will see the major benefits of nitrogen.

* This post was edited 08/21/12 03:23pm by SprinterDriver *

wolfe10

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Posted: 08/21/12 03:24pm Link  |  Print  |  Notify Moderator

SprinterDriver wrote:

I've run 4 sets of tires with nitrogen, and have gotten more than 130,000 out of each set, and 20% better fuel mileage.


Please explain such a huge increase in MPG. I ASSUME you are running the same tire pressure, just different gasses.

SprinterDriver

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Posted: 08/25/12 06:56pm Link  |  Print  |  Notify Moderator

wolfe10 wrote:

SprinterDriver wrote:

I've run 4 sets of tires with nitrogen, and have gotten more than 130,000 out of each set, and 20% better fuel mileage.


Please explain such a huge increase in MPG. I ASSUME you are running the same tire pressure, just different gasses.
The same Cold Tire Pressure, yes. The explanation would involve several things, but most notably it would be the lack of water vapor in the tires, which translates to minimal circumferential growth when hot and less circumferential changes throughout the various driving conditions. The tires stay closer to the proper and ideal pressures at a wide variety of driving conditions such as Texas and the Southwest in the heat, in the mountains at slower driving speeds and cooler temperatures and lower atmospheric pressures. Pressure fluctuations occur at different temperatures and altitudes, of course, but they are not as pronounced with nitrogen. With air I got 20.2 MPG, with nitrogen it's 24.5 MPG.

wolfe10

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Posted: 08/25/12 07:17pm Link  |  Print  |  Notify Moderator

I agree Nitrogen and DRY air are very similar in terms of PSI change for a given temperature change. Wet air/water in air is a very different beast.

So, let's agree that air with water vapor is BAD, and dry air is good and Nitrogen has a few additional attributes over dry air. BUT the biggest difference in performance is between wet air and dry air, not between dry air and Nitrogen.

CapriRacer

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Posted: 08/26/12 03:51am Link  |  Print  |  Notify Moderator

A couple of thoughts:

1) Pretty much all gases behave like ideal gases at the temperatures and pressure we are discussing - and that includes water vapor. There is no difference between "dry" air and "wet" air - with the exception of when water is precipitating (raining) inside the tire.

2) Water vapor permeates through the tire and eventually comes into equilibrium with the air outside.

3) I have only seen water inside a tire that was freshly mounted and had water in it to beginning with. I have NEVER seen standing water in a tire that is more than a few days old.

jadatis

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Posted: 08/27/12 04:06am Link  |  Print  |  Notify Moderator

CapriRacer wrote:

A couple of thoughts:

1) Pretty much all gases behave like ideal gases at the temperatures and pressure we are discussing - and that includes water vapor. There is no difference between "dry" air and "wet" air - with the exception of when water is precipitating (raining) inside the tire.

2) Water vapor permeates through the tire and eventually comes into equilibrium with the air outside.

3) I have only seen water inside a tire that was freshly mounted and had water in it to beginning with. I have NEVER seen standing water in a tire that is more than a few days old.


I am trying to find out how water goes trough the rubber of the tire when it is a gas of liquid. My feeling about it is, that as gas it might go with the same speed as Oxigen ( further O2) , But as liquid probably does not go trough the rubber. In any case , as a gas the paritial pressure law counts for it.

This could lead to a interchanche by temperature chanches, so that if you have water in the tire , it goes out by itself , or comes in to the tire at the log run.

The experience number 3 of capri-racer would say that it goes out in the long run, in his example even in a few days.
But I also have seen coming water out of the valve of a bycicle-tire when letting out air for replacing the tire, but can also have been in the opening of it because of no cap screwed on it.

Thoug I also dont see the benefit of N2 (Nitrogen) filling, I have seen a few more messages of less pressure rising with it filled.
Though you should not trust everything that is written, there must be some point in it.
The only thing , I can explain it by, is that at sertain temperature and pressures , the water ( H2O) goes over from liquid to gas, wich takes more space, so higher pressure then dry air.
Also the O2 and N2 can disolve in the liquid H2O and go out of it at other temperatures. Water is for the temperature range in tires not an ideal gas, because it turnes to liquid at lower temperature, depending on the pressure. N2 and O2 stay gas .

* This post was edited 08/27/12 04:19am by jadatis *

SprinterDriver

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Posted: 08/28/12 06:24pm Link  |  Print  |  Notify Moderator

wolfe10 wrote:

I agree Nitrogen and DRY air are very similar in terms of PSI change for a given temperature change. Wet air/water in air is a very different beast.

So, let's agree that air with water vapor is BAD, and dry air is good and Nitrogen has a few additional attributes over dry air. BUT the biggest difference in performance is between wet air and dry air, not between dry air and Nitrogen.


I would say that is correct. People sometimes confuse water vapor and liquid water, but they are very different in how they behave. Wet air doesn't mean standing water, it simply means air with high humidity. It can and does condense inside a tire to form liquid water, but it doesn't take much of a temperature rise to get it to become water vapor again.

The other big performance factor is nitrogen leaks out of the tire at a slower rate than air, so it stays properly inflated for longer periods. Of course, being anal about tire pressures using air accomplishes the same thing.

With air, you need to check your tire pressure once a week, maybe more often depending on where you drive. With nitrogen, checking the pressure weekly is a waste of time, and you'll let out more nitrogen checking the pressure than will leak out on its own. Once a month is plenty with nitrogen.

CapriRacer

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Posted: 08/29/12 05:13am Link  |  Print  |  Notify Moderator

SprinterDriver wrote:

......I would say that is correct. People sometimes confuse water vapor and liquid water, but they are very different in how they behave. Wet air doesn't mean standing water, it simply means air with high humidity. It can and does condense inside a tire to form liquid water........


My experience is that water rarely condenses out of air in tires. Remember that air is compressed in another tank, where the water condenses, then is pumped into the tire at a lower pressure. Then once in the tire, the water vapor seeps through the tire and reaches equilbrium with the outside water vapor.


SprinterDriver wrote:

......The other big performance factor is nitrogen leaks out of the tire at a slower rate than air, so it stays properly inflated for longer periods. Of course, being anal about tire pressures using air accomplishes the same thing.

With air, you need to check your tire pressure once a week, maybe more often depending on where you drive. With nitrogen, checking the pressure weekly is a waste of time, and you'll let out more nitrogen checking the pressure than will leak out on its own. Once a month is plenty with nitrogen.


Unfortunately, the diffision rates of both air and nitrogen through tires is close enough to treat as the same.

Consumer Resports Study on Nitrogen and Pressure Loss

The Consumer Reports study showed a pressure loss of 3.5 psi over the course of a year - vs nitrogen which was 2.2 psi. Not only are both pressure losses small, but a 1.2 psi difference over a year is small enough to ignore.

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