Nitrogen or Compressed Air

[MICAH1]

The wife and I went to our local COSTCO to purchase four new tires for the car, and was told that they now inflate their tires with nitrogen. The tech said that you get a better ride, better gas mileage, and extend the life of the rubber. Is there anyone out there who uses nitrogen in their tires for the Opel, and if so what are the true pros and cons?????

[wrench459]

Nitrogen (N2) 78 .080
Oxygen (O2) 20 .946
Argon (Ar) 0 .934
Carbon Dioxide (CO2) 0 .038
Neon (Ne) 0 .00182
Helium (He) 0 .000524
Methane (CH4) 0 .00015
Krypton (Kr) 0 .000114
Hydrogen (H2) 0 .00005
In plain old air you be the judge.

[MICAH1]

Hey Wrench,
I appreciate all the scientific values........... but how about some dialog??

[BQS4]

Thomas;
Try to think of it this way, if your tire is down a little bit, where are you going to be able to pull in to find a Nitrogen pump? I'd rather stick with air...

[wrench459]

They say the nitrogen doesn't have the pressure changes like typical air has.
My thoughts are so what the pressure increases only a few pounds when the tire gets hot.

[MICAH1]

Hey Gene,
You know that was my first question to the tech, and his reply was that it is okay to use regular compressed air if a tire needed it. Now these nitrogen filled tires are not on my GT, but one of the other cars. Just wondering if anyone fills their Opel tires with it.

[jeff denton]

It's an old trick. Yes I absolutely do use only nitrogen in my tires. On the race cars, anyway. Not for the reasons given by your tech, though. Here's why it's good for stock car racing: The size of the tire is a very critical tuning tool. The actual circumference. This is adjusted by air pressure, once you have the tire initially "grown" to the size you want. Half a PSI makes a difference, would you believe.
So we want that tire to pretty much STAY that size (circumference) throughout the race, and it is getting hotter all the time, may cool down during a caution, etc. They get hot enough to burn you if you touch them.
If you put air in your tires and get your circumference just so, which includes "stagger" (circumference is purposely different, maybe even four inches) from side to side, and all your tires are at, say, 30 psi (but all four tires rarely run the same pressure) and then go run hard, hot laps, when you get back and check everything, you'll find the pressures may have radically changed. Especially on the right side, those tires are working harder and got hotter. Guess what happened to the tire size, and your precious stagger? Way off.
If you use nitrogen it will still happen but not even half as much. It makes it easier to predict how much your tires will grow, if at all, and adjust your cold pressure according to your experience.
This is why we take notes, chart all tire pressures and size before (cold) and after (hot) every race. By referring to the notes it helps set the car up for the next run.
I haven't tried other gases. Would be fun to try helium if the car is heavy. Don't know what that would do to the pressure when hot, though...
Better yet, maybe hydrogen. In a good crash the fans might get a little extra bang for their buck.
Oh, also, often nitrogen gets used when it's more convenient to use than compressed air. For instance, it might run an air tool briefly in a place where there is no air compressor available or allowed. We use it a lot in the balloon business.

[michaedo]

nitrogen molecules are supposedly bigger than plain old air,
therefore don't leak out through the rubber molecules that
make up the tire, meaning less need to be filling up the tires.
All said and done sounds like a marketing gimmick. Now, when
they start talking about helium to fill up tires I might be
interested. I wonder if it would lighten the load?

[OpelNewb]

Nitrogen is the way to go. They have been using it in airplane tires for a long time. It is true that it doesn't react the same to temp changes.

If your tire goes low you could still fill it with air. You will find by switching to the nitrogen you don't have to add to the tires. Unless you run over something and get a leak.

[wrench459]

Interesting question about helium does the tire change octaves during a burn out? :-)
Another thing is the weather and altitude. I was amazed at the difference in setups from a Fla. 32 feet above to a Georgia setup which is around 900 ft above.

[namba209]

Jeff hit it on the nose. Nitrogen, being an inert gas has more stable characteristics than regular atmospheric air. That is, it is less prone to thermal reaction/contraction than plain air. Helium is a no-no, it leaks through the rubber and won't last too long. We used Nitrogen in all tires and accumulators and other areas where compressed air was needed on the Blackbird. During the development stages of the U-2 Helium was tried on the tires. but didn't keep the tires inflated during the long flights.

[jeff denton]

There was an old truck driving joke about helium. Goes kinda like this, if I recall: A tanker truck full of helium gets red lighted at the weigh station. "Too heavy" says the officer. The driver asked "so what do I do, let some out or put more in?"
Interesting concept about nitrogen staying inside the tire longer. All I know is our race car tires rarely stay up overnight. Even with nitrogen in them.
Maybe there's something to it. But I think it's mostly a gimmick. I assume they have to charge extra to put nitrogen in? A bottle of nitrogen costs peanuts compared to a bottle of helium or argon/CO2. The price of helium has skyrocketed. We go through about a thousand dollars a month worth.
By the way, I can't tell the difference in weight between a full bottle and an empty one. I move four big bottles a week in and out of the party store.
We used nitrogen in heavy equipment hydraulic accumulators. Because you have to charge them to hydraulic pressure, up to 2000 psi. Try that with your air compressor. When you start with a full bottle at 2200 psi you might only get one big accumulator charged, then don't have enough to do the next one. Need a fresh bottle. There's still over 1800 psi, "hey boss, can we take this bottle to the track tonight?"

[traytodd]

1. N2 is not an inert gas, neon, argon, helium, etc. are inert gases. N2 is less reactive than O2 but judging from the fact that tires last years and are more prone to UV damage than O2 damage, I would not worry about the reactivity. Ozone (O3) is another story.

2. Most gases very nearly obey the ideal gas low. PV=nRT

3. The heat capacity of gases will vary with the number of atoms in the molecule since the degrees of freedom are 3n-1 where n is the number of atoms. Hence CO2 will have a higher heat than N2. CH4 will be even greater. However, there is very little difference in the heat capacities of diatomic molecules. Since air contains very little (<2%) non-diatomics, its heat capacity is essentially determined by N2 & O2.

4. The heat capacities of the N2, O2 and air near room temperature are:
N2 1.040 kJ/kg/°C
O2 0.918 kJ/kg/°C
Air 1.005 kJ/kg/°C
Before you jump to conclusions though, remember the pressure in the tire is determined by the moles of gas in the tire, that is the number of molecules not their mass. So we need to remove the mass from the number to get a true comparison. The masses for N2:O2:air 28:32:28.8 amu. So the heat capacities times relative masses are respectively 29.12:29.376:28.94. N2 has only a 0.6% better heat capacity than air. Hence the difference in performance between air and N2 is miniscule. For a 50°C (90°F) rise in tire temperature of an air filled tire, an N2 fill tire will rise 49.7°C (89.5°F), only half a degree F difference.

I would not pay to have tires filled with N2. If it is free, it will not hurt but I have not seen a free bottle of N2 yet.

Terry

[namba209]

Originally Posted by jeff denton We used nitrogen in heavy equipment hydraulic accumulators. Because you have to charge them to hydraulic pressure, up to 2000 psi. Try that with your air compressor. When you start with a full bottle at 2200 psi you might only get one big accumulator charged, then don't have enough to do the next one. Need a fresh bottle. There's still over 1800 psi, "hey boss, can we take this bottle to the track tonight?"

Jeff, in the USAF we used 2 bottle and 6 bottle carts with all bottles charged to 3000 psi. Hydraulic reservoirs, tires, accumulators and landing gear struts are all charged with nitrogen. The big thing with using nitrogen in the tires is a smaller increase in pressure 15 minutes after the last application of braking action. It was used exclusivly in the Blackbird, but then with 400+ psi in the 32 ply main landing gear tires, if one does blow, there's no fiery explosion, just a big bang. Had that happen to me ONE time.

[oppositelock]

I work in the world of professional road racing. Last year I worked for an ALMS team, this year in Speed World Challenge. Yes, we use nitrogen in the tires and yes it's for more stable tire pressures. The real reason is it's drier. Plain air can have a lot of moisture in it and when the tire heats up that's what's really causing the fluctuation in air pressure. A lot of the tracks we race at it can be really humid. Sebring in March, for example, can easily be 60-70% ambient humidity. We have a guage we can check the humidity of the air in the tires. When we get new tires mounted at the tire truck they just fill them with air. Then we have to purge them 2 or 3 times with nitrogen to get the humidity in the tire down to no more than about 15%. No point in getting any closer to 0% than that, there's very little gain. With fully purged, nitrogen filled tires you will still get pressure rise as the tire heats up (and racing tires heat up a lot) but it's not so much and it's more predictable than plain, moisture filled air.
Even in an area with low ambient humidity (Denver or New Mexico, for example) the air coming from the air compressor tank can have a lot of moisture in it, especially if it doesn't get drained regularly. And it's not good enough to just drain the air out and refill with nitrogen. You can still have 35-40% humidity in the tire which is hardly an improvement. You need to purge 2 or 3 times to be effective. I doubt Costco is doing that. Which, on top of the fact that it's hardly a critical thing for a street car (the tires don't heat up much compared to a racing tire, most people don't monitor their pressures that closely or adjust the pressures to tune the handling of the car, etc.) makes me think it's a gimmick in this case. When the tech said," ... a better ride, better gas mileage, and extend the life of the rubber..." that was all BS. None of that is true except maybe the tire pressures might be more likely to stay in proper specs which could contribute to those things in a small way. But you can easily achieve the same thing with plain air in your tires if you just check your tire pressures regularly, which you should be doing anyway...

[opelgtmaster3]

in the navy we use nitrogen. we mainly use them on the f-18s like struts, tail hook, landing gear and tires.

[hrcollinsjr]

Originally Posted by oppositelock ... When the tech said," ... a better ride, better gas mileage, and extend the life of the rubber..." that was all BS.

It probably IS true, under laboratory conditions and he didn't say how much. Misleading maybe/definitely.

[Redskinsjbs]

First of all, the helium would make no relative difference in the mass of the car, or wheel for that matter. If you recall, the reason why balloons float is that the volume of air they displace weighs more (has more mass if you factor out gravity) than the entire balloon's mass.

In the case of a tire, I am pretty sure that a few cubic feet of air has much much less mass than that of the rubber in the tire. And when you factor in the fact that tire needs to be filled with another gas in order to make it not implode, the weight difference would be much less.

I like the point about the moisture being the main reason for tire expansion. I have some expeirience with this. My family was taking a cross country road trip, and as a result, the tires needed to be filled a couple of times. We first stopped in Arizona to fill up the tires, and since we had been driving for some time and the tires were hot, my dad made sure that he wouldn't overinflate the tires. Well a couple of miles down the road, we ran into a huge pothole at highway speed. BOOM, there went the tires. After a set of four new tires and a couple of hours, we were off.

The funny thing was that once we got back to DC, the tires just went flat. They had stayed inflated the whole way home, but just deflated overnight once we got there. The reason I attributed this to was that the DC air being around 95% humidity had caused the 10% humidity Arizona air to deflate far more than we had thought.

[OpelNewb]

The guy at the Costco that said they would last longer is correct about that statement. The drier the air is in the tire the less likely it would be to rot. I wish I still had these tires I just took off my mieghbors son's go kart. They had stayed wet so long on the inside that the rubber was more like gel inside the tire. The outside was still your normal dried out self from sitting in the sun. The combination of the 2 made for a go kart tire that actually came apart at only 20mph.

[MICAH1]

Dam, I love this site!!!!!!!

I asked for dialogue and I got really great detail conversation. Received my answer, and was reeducated about the use of nitrogen through the personal experience of you folks who responded to this thread..

Hell, Einstein ain't dead !!!! He is alive and well in the minds of the people of this site.....

[Dennis Texas]

We use it in the field to pressurize the huge cylinders that act like shocks on pulverisers wheels in commercial coal generation of electricity. Being an inert gas it displaces air or breathable content in low places, it is odorless so even though it is a inert gas it could kill you it is heavier than air if you were to breathe it in and fill your lungs. Precautions would be, just to use in open spaces no confined enclosed spaces and don't breathe the fumes.

[oppositelock]

Originally Posted by OpelNewb The guy at the Costco that said they would last longer is correct about that statement. The drier the air is in the tire the less likely it would be to rot.

That's a good point, I hadn't considered that. Does moisture really rot tires? I know UV light does. You've all seen old tires that have sat out in the sun too long, full of cracks.

To add to the many uses for nitrogen, a long time ago I used to carry an air compressor in my service truck at rallies but no more. Now I just carry a big nitrogen bottle for running air tools, filling tires, and most important of all, charging up my potato cannon. Way more compact and quiet than an air compressor and a bottle will usually last a couple of rally weekends.
At the racetrack we use nitrogen for everything, running air tools, on board air jacks, air guns, filling tires as discussed before. All the teams have an account with Airgas for the year and they bring bottles to each racetrack. A typical ALMS team will use 8-10 bottles each race, more if they run multiple cars or if it's a long race.

[trlmr]

I would like to give a grade of A+ to oppositelock. After a few posts you can usually tell if someone really knows what he is talking about. As far as putting nitrogen in aircraft struts they do it for the same reason. It gets cold at altitude and you don't want them frozen when you hit the pavement. I know they put nitrogen in the tires too, but I don't know if there is a reason other than they have a bottle handy. I am talking about general aviation here - I don't have anything to do with commercial aviation. The tire places use a special compressor (I doubt that it is 100% nitrogen) to inflate their tires with nitrogen - not bottles.

[Paul]

Originally Posted by oppositelock That's a good point, I hadn't considered that. Does moisture really rot tires? I know UV light does. You've all seen old tires that have sat out in the sun too long, full of cracks.

There is *some* validity to the longevity issue with Nitrogen. The Oxygen will, to some degree, react with the rubber on the inside of the tire causing it to age. However, I don't think one would see a large improvement, especially if you are like me and go through tires every 2 to 3 years. However, if a set of tires usually lasts you 5 to 6 years and you buy new ones because they begin to dry rot instead of wear out... then using Nitrogen might make a difference...

I concur with the use of dry Nitrogen, expanding less and more uniformly under race/autocross conditions...

[traytodd]

There will be very little difference in the thermodynamic performance of N2 and dry air. The operative work here is dry. It is the condensibility of water that is at the root of this problem. On compression, it liquifies to reduce the pressure, hence builds up over time as a liquid in the bottom of the compressor. As a result the air coming out of the compressor is saturated. So the tire gets filled with saturated air (100% humidty). If the temperature drops, the water condenses. So if you check the tire on a colder day than when it is filled the pressure will be low, you add more air. The next time it heats up, the water evaporates and raises the pressure in the tire above what was desired.

Someone said that the tire stores are using compressors that separate N2 from air. Parker sells a membrane filter/compressor that does this. I would think they are expensive, hence there is probably an added charge for a nitrogen fill that is either buried into the cost of the tire or added as an optional expense. I would think that a cheaper approach would be to add a coelescing filter or a hydrophopic filter on a standard air compressor. These would remove most of the excess water and mimimize the problem.

Terry