Definitive Nitrogen Inflation Discussion

Nice write up, You have my vote but you forgot number 6

6) Mining Mobile Equipment, We use nitrogen in most of our large underground mining equipment, some of the reasons that the nitrogen is a non-flammable gas like you stated in numbers 1) and 2) a large tyre fire underground is something you don't want to be involved with, With nitrogen the tyre pressures are more predictable with 50Tonne plus loads than compressed air is like you stated in number 3)

I see you pay an extra $5.00 to fill your tyre with nitrogen at most major tyre Retailers also, money well spent IMO if your spending $400+ for a tyre anyways

Here is a quick pic of a R2900, It's not quite the baby of the fleet but it's getting there, the tyres alone over 6' tall and can hold alot of nitrogen
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thats not your daily driver is it Pap ?

 

The only reason I use Nitrogen is to eliminate water (condensation from compressed air) from in the tires on race cars only.
That said, I have found that unless a vacuum is put on the tires after the bead is set in place there will be no benifit at all.
As in the A/C systems, water will turn to a vapor when put under a vac. for a period of time and can then be eliminated. It will not come out after purging it, anyone that has broke tires down knows how much water is inside some of these tires coming off.
With a good racing type wheel the tire will turn to an octagon and still hang on the bead of the wheel. The tire has to be fresh to do this as the sidewall takes quite a stress when in this shape.
The result is tire pressure growth that is perdictable and limited to around 3-4 pounds on say an F40 sized wheel. This is compared to pressure growth of 12-14 pounds between hot and cold when filled with compressed air done in a humid climate. If soap and water is used to lube the tire bead upon install,the effects are greater as that water stays in the tire.
Yes, having the tanks at the track is a nice side benifit for use as compressed air and to hold the canopy on the trailer from becoming a kite.
Having the availabilty of excessive (above 200 psi) pressure to operate 3/4 drive impact tools for the center lock wheels is a must when the wheels are hot.
Oxygen breaking down the rubber in the tires? Horse ****.
I have also straped on my old Scuba tanks and adapted the mouth piece hose to a paint gun. There was a time when lacquer paint was not considered harmful and everyone knew they had to wet sand and buff it anyway so.... Scuba air is dried quite well, the TR-3 needed new paint, there wasnt much of a wind (good painting weather). Turned out beautiful and then I noticed the neighbor had her cloths hung out on the line!

Dave

 

If I could drive it out of the mine..............it would be.

 

I do what Dave does for my race car. I have my own tire machine and use waterless soap sparingly and mostly dry mount tires. I have some special tools that make this possible. As dave posted the problem is water. There is more or less water in your air compressor lines depending on several conditions which will put water into your tire. I use N2 tank to run run airtools and quickly air up when an air compressor is not available in the pits. There is value here just not for street use.

 

Didn't read all of the eng-tips posts, but I know a bit about this subject.

Tires DO oxidize from the inside out. The tread rubber protects it pretty well from the outside, but the inside of the carcas gets attacked from the inside out.

There is a proposal for a tire aging test to the governement to address some of these concerns. But the aging mechanism is oxidizing from the inside out, dependent on temperature.

High performance tires are not very sensitive because they have tread caps built into the tire construction. So for the most part high buck F-car tires probably don't care.

Where it could make a difference is on trailer tires. They age vs. wear out normally. They aren't necessarily made with tread caps. So they do benefit. I also put nitrogen in my tow vehicle truck tires. Same reason.

All the benefits the guy at the tire shop says are bull. The only good reason to do it is to prevent aging and that only on tires that will age more than wear.

And to get the benefit, set bead with N2, deflate, reinflate with N2. You'll have very little O2 in your tire at that point.

 

I don't know about F 40's but I run 28/18 lbs in my 1500 pound Lotus so I can't imagine 12-14 pounds of extra pressure when hot.

Ken

 

Yes water vapor is a gas subject to general gas law. Water however is a liquid not subject to the GGL until it becomes hot enough to vaporize into a gas. There in lie the rub. Think of it this way...a block of Co2 acts differently than it does when it sublimates into a gas a room temp. Or do the chemistry book research. I'm too old and can't remember how to prove this to you and I am too lazy to look it up. Suffice it to say all the pro race teams probably are not wrong. Running airtools on N2 is a convenience. Pro teams with thousands to millions of dollars in budget can afford an air compressor and a generator to run it. They use N2 for tires for a reason.

 

And for all these years....?

DHarm / jselevan
Sorry, I was looking at the discussion in the context of Ferrari tires. Trailer tires are a great example of very long life where the degrading effects of oxygen might come into play. I do not know enough about this to accurately comment on that lenght of time. I was thinking about tires on Ferrari's with a life cycle of 5 yrs or race cars at 5 months.


"Dave - the liquid water that you encounter when explosively deflating a tire (as in dismounting by popping the bead) is due to the momentary cooling of an expanding gas."

Negitive.
1) One has to relieve the pressure to break a bead. Nothing explosive about it. Back in 72 the owner of the Mobil station would scream at us if we just pulled the valve core and let it scream. He was deaf as a post but he said it hurt his ears. We were only allowed to let the air hiss out.
2) I remember breaking down tires (I graduated from that task in short order as that is the rookie job at most shops) where there was a full cup of water inside the tire if not more.
3) Anyone that has had the job of draining the shop compressor at the end of the day will tell you how much water condenses in that tank and in the course of the day is put through air tools and into tires. Back in Mn. we kept the floor sqeegy next to the compressor.

Agreed, anyone saying they can measure 1/4 pound accurately let alone feel it in handling is blowing sunshine and looking for attention. Two pounds, hell yes! FBB makes a fair and accurate statement here.
Compare highly dried air and dry Nitrogen and your point is valid and accurate. Compare the thermo expansion of a tire, pulled to vacuum and filled with N2 vs one filled with shop compressed air laden with the inevidable water that comes with it and the arguement falls apart. Practical experiance not theory.

We ran, on average in the 21 to 32 pound range (slicks) depending on the track, the car, ambiant conditions, driver skill and tire age. With 10% pressure growth things can be difficult to predict, with 50% is down right ugly.

Dave

 

I just started thinking about all the hype. I know the good reasons for using it, and outside of water vapor, the other reasons are somewhat marginal. Tires do oxidise inside, and I have seen as much as a whole handful of rubber dust, or tiny black rubber balls inside of tires I broke down, but I degress, it takes years. Trailer tires would get a slight benifit. In general aviation they use it. Probably for most of those slightly marginal avantages, but probably more to keep moisture out. Fire safety real seems quite a stretch, but its the space shuttle, so whats a million dollars here or there for some gas.

Now up here in a really cold winter, its possible to get quite an amount of water out of a hose when you try to fill a tire. I generally have never seen over two cups or so, but thats quite a bit of weight rolling around free like a loose cannon. I once found almost a gallon in one tire, boy was that a hard one to bubble balance. It just kept sloshing around, and thats how I found it. You could hold the wheel/tire flat and feel the water run around. But the thought of it freezing into a solid lump is even more disconcerting.

But I was wondering if the hype hasnt gotten way out of hand. You find many stations today want to charge money to use theyre air. So next it will cost $5 to check your tires and refill with N2 down at Amoco? Will Starbucks start offereing N2 to thier customers? Then you can have that green feeling when you see those green valve stem caps. Seriously, I heard someone say N2 was safer for the environment, thats why you get green caps! Tires Plus is selling N2, claiming its a larger MOLECULE and wont come through the tire. They even have a big poster made up with a picture of a N2 atom with the word MOLECULE. I heard the guys talking on the phone telling everyone about N2 MOLECULES until I wanted to slap somebody. At least they didnt use the word "thingy" in any sentences.

 

An "N2 atom?" N2 is molecular nitrogen.

 

Let’s add some quantitative aspects to this discussion by looking at the problem from Dalton’s point of view. Dalton’s rule of additive pressures says that the total pressure of a mixture of gases is the sum of the partial pressures of the individual constituents

The partial pressure due to any of the gases can be determined by use of the ideal gas law: P = mRT/V where m is the mass of that gas component in lbm, R is the gas constant for that gas gotten from dividing the universal gas constant by its molecular weight, T is the temperature in Rankine units, and V is the volume of the tank in cubic feet. Thus to get the pressure of a tank of several gases, you can apply the gas law for each constituent and add the pressures together. Or, you could find the gas constant that represents the mixture of gases and just do the computation once. The latter is done for air as it is a mixture of gases. But it could also be done on a specie basis and pressures summed.

Think of a tank as the volume of a tire. Further, let’s assume the tire is rigid because if you don’t the computations gets too complex. Also assume there is no thermal expansion of said tire so volume does not change from that standpoint.

First off, let’s get a rough estimate of the volume of a tire, say about 225/50-16 in size. If you assume the tire cross section to be a rectangle, the height and width of it are 4.43 inches and 8.86 inches respectively. The volume of the tire, V is

V = pi * D * 4.43 * 8.86, where D = 16 + 4.43

V = 2518 cubic inches or 1.46 cubic feet.

Now let’s get to the thermodynamics of the issue. First off, let’s determine the maximum amount of water vapor the tire at 200 F can possibly hold, that is to say the volume is fully saturated at 200 F. Using steam tables the specific volume of saturated steam at 200 F is 33.67 ft**3/lbm. Thus the density is the reciprocal, 0.0297 lbm/ft**3.

The maximum amount of water vapor then is:

M = 0.0297 * 1.46 = 0.0434 lbm

The partial pressure of the vapor is:

P = m*R*T/V = .0434*85.7*660/1.46 = 1680 psf or 11.7 psia
The partial pressure due to the dry air in the tire if initially inflated to 30 psig at 70 F raised to 200 F is:

P2 = P1*T2/T1 = 44.7*660/530 = 55.7 psia = 41.0 psig

According to Dalton’s law, the total pressure if 0.0434 lbm of water all evaporated is:

P = 55.7 + 11.7 = 67.4 psia or 52.7 psig.

That is a huge difference due to the water vapor. But let’s go one step further. Let’s assume the tire is initially filled with ‘air’ at 90 F and 80% relative humidity. How much water vapor is in the tire?

Phi = 0.80 = Pv/Ps Humidity (phi) is ratio of vapor pressure to saturation pressure. From this we compute Pv, the vapor pressure.

Pv = .80 * Ps = .80 * .6980, where .6980 is saturation pressure at 90 F taken from standard steam tables.

Pv = 0.5584 psia. Using steam tables again, the dew point is 83 F.

Going back to Dalton’s law we can compute the mass of water vapor in the tire:

M = Pv*V/(R*T) = .5584*144*1.46/(85.7*550) = 0.00249 lbm or 0.0382 fluid ounce.

So using ordinary air at 90 F and 80% relative humidity, your pressure can vary 0.558 psi due to the vaporization of liquid water.

Tires do deflate because they are porous. Tires also show lower pressure if their temperature drops below the dew point, that in this case is 83 F. Therefore, you pump them up from time to time. Your moisture level rises; your pressure becomes more variable as time passes by.

 

Lawrence,
Excellent post!

Birdman

 

My mistake. I mistakenly used the term N2 as was used previously in this thread, whereas TiresPlus in simply using the term Nitrogen.

 

Great science and it does apply. But you are thinking like a scientist narrowing down parameters to digestible bites. You see you need to think like a tire monkey, "eat banana"..."put on tire". Not only is there the issue of Dalton's law but the real issue is the ounce or more of water put into the tire by the monkey when he soaps it for mounting. Now you got 100% humidity in there and extra water in the tire. Increasing heat does what it does with the general gas law and some water goes into heat and you get more pressure and all of this is unpredicatable because you got some much crap in the tire that you can't apply dalton's law with one clean gas or two. These monkeys are lazy as hell and do not want to take the time to drymount or use expensive waterless soap. Sorry for not responing earlier I just got back from racing this weekend. I corded a race tire and had to have the tire shop at the track put on some new rubber. As par for the course even these pros who do nothing but race tires used soapy water to mount the tire. Much to their credit however they were the first monkeys I have ever seen actually change the setting on the tire balancer to give me a dynamic xy balance as opposed to the more standard static balalce of the lazy monkey who just puts your tire on the machine. But...that's another thread. By the way you guys don't listen to me I'm just a home mechanic and mediocre club racer. DaveHelms is a real Ferrari shop pro with lots of race clients and quite a list of credentials and if you ever get into a real jam he is the guy to help you out. He has tools you only read about and he know how to use them. So Dave is giving you guys a tip here that N2 and no water works in race tires.