Can You Say Cold??

I was driving home last night in my Jeep watching the tire pressure slowly drop wondering how low it could go before the tires started coming off the rims. Was still not as cold as last January in Pinkham Notch when the belts froze though.

Joe

 

and i thought 7 degrees on my way to school this morning was cold

 

North Carolina poster dropping in to say that it was freezing over here the past few days, got down to 5 I think with a wind chill below 0. Something like that. Anyways, your mountain home is awesome, I hope you enjoy your -50 degree weather and I''m much more thankful for mid-20s now.

 

Steve-

How much does a nitrogen fill cost? Would nitrogen really help to keep your tire pressures up when it gets cold? It's a gas, just like plain old air, and subject to the same rules- PV=NRT, if I remember anything from chemistry class. As temp decreases, so does pressure if gas volume is kept constant. That's why Birdman and his fellow SCUBA divers don't keep full tanks in the trunk during the summer.

Oh, and let me say- MINUS 56 DEGREES!! YIKES!!!

-Gio P

 

Steve,
I don't know where you heard this, but Gio is right. Any two gasses at the same pressure/volume/temperature will change pressure as a function of temperature exactly the same, as described by the ideal gas law PV=nRT. Do a google on PV=nRT.

Furthermore, even if this were not true, air is 79% nitrogen. The difference between the two in terms of temperature would be minimal.

The only advantage I have ever heard for putting nitrogen in tires is not for the benefits of nitrogen but for the benefits of the lack of oxygen. Oxygen oxidizes the rubber and will (if you wait long enough) dry rot the tires more than a lack of oxygen. But most people wear out the treads long before that would happen.

Hey, we could fill our tires with helium and reduce the unsprung mass of our wheels though!

Birdman

 

>There are advantages to inflating tires with nitrogen rather than compressed air, but not all these advantages will apply in all applications. Advantages of inflating tires with nitrogen rather than compressed air:

1. Slower rate of pressure loss. The rubber used for tubes & inner liners in tubeless tires is not 100% impermeable, therefore some pressure loss can be expected over time. This is one reason why regular pressure checks are necessary. Due to its molecular structure, nitrogen bleeds through the inner liner or tube at a slower rate than regular compressed air.

2. Cooler running temperatures. Tires inflated with nitrogen will run cooler than those inflated with compressed air. There can be significant advantages associated with cooler running temperatures:

a. Improved tread life. Reducing a tire's running temperature will increase its tread life. The amount of increased tread life will depend on the amount running temperatures are reduced by using nitrogen rather than compressed air for inflation. The amount by which running temperatures are reduced with nitrogen inflation compared to normal compressed air will depend on the specific application. As a rule of thumb, the closer a tire is to its maximum heat handling capabilities, the greater the reduction in running temperatures will be experienced with nitrogen inflation when compared to inflation with normal compressed air.

b. Reduced incidence of tire damage caused by excess heat. In applications where tires are run at, near, or over their maximum rated capabilities for load (or speed), heat related tire damage is common. The reduction of running temperatures with nitrogen inflation compared to compressed air should reduce the incidence of such damage.

3. Reduced pressure build-up. This is why nitrogen inflation is very common in tires used for racing. Running a tire produces heat; this heat will cause an increase in pressure. The amount of pressure increase will depend upon the amount of heat produced. In racing applications, the high levels of grip provided by race tires produce considerable heat. The heat produced by this friction, as well as the flexing of the tire, will produce a large amount of pressure build-up. In race tires the pressure build-up can represent up to 50% of the cold inflation pressure. With nitrogen inflation there is less pressure build-up due to heat.

All conditions being the same, the difference in tire running temperatures when comparing nitrogen with compressed air for tire inflation is due to the presence of water in compressed air more than any other factor. As a tire is run, flexing of the sidewalls and tread, as well as the friction between the tread and the road surface produces heat regardless of what gas is used to inflate the tire. The water molecules in the compressed air behave quite differently compared to nitrogen molecules when exposed to the heat produced by the running of a tire. Water molecules become much more "excited" by the heat generated by the running of a tire, creating more heat & pressure build-up compared to a nitrogen inflated tire.

Compressed air, less the water vapor (i.e. "dry air") will provide cooler tire running temperatures compared to normal compressed air. Compressed air that is completely free of water vapor will provide very similar levels of reduced running temperatures & reduced pressure build-up compared to normal compressed air inflation. Dry air will bleed through inner liners & tubes at the same rate as normal compressed air.

4. Reduced amount of oxidization of wheels. Oxidization (rusting) of wheels is a common problem. Rusting will only occur in the presence of water & oxygen. In theory nitrogen inflation should prevent rusting of rims as there is no water vapor or oxygen present.

 

Dennis,
I'm questioning the scientific reasoning behind some of what you said, all in good humor...not trying to argue.

Oxygen (atomic number 8) is a slightly larger molecule than nitrogen (atomic #7) so in fact, oxygen in theory should seep through rubber SLOWER than nitrogen. Since air is 79% nitrogen and the only other significant gas in air is oxygen, the above statement makes me scratch my head in wonder. Perhaps the oxygen portion of the air in tires is not actually leaking, but being consumed by oxidation, which is much more likely.

I'm not saying I don't believe you but I would like to know how this happens. The heat has to go someplace. Nitrogen doesn't make it vanish. The only explanation I can think of is that nitrogen conducts heat better than oxygen, so nitrogen is somewhat better at conducting heat from the inside of the tire to the wheel, where it can dissipate better. Being a smaller molecule, it is in fact quite possible that this is the case. Smaller molecules conduct heat better (in general) in gasses than larger molecules. This is the reason many divers working in very cold water put argon in their drysuits...it is a large molecule that doesn't conduct heat well and insulates better. Still, again, I'm pointing out that air is mostly nitrogen, and the difference in size of the molecule between nitrogen and oxygen ain't much.

This I believe. I would bet that dry air is essentially the same as using nitrogen. The water vapor is probably the issue more than the tiny fraction of oxygen in terms of conductivity of heat.

I completely agree.

Birdman

 

Wow- I am continually impressed by the knowledge floating around on this forum! I did some web searching and pretty much every second-order advantage that Dennis described is touted on every site that sells nitrogen inflation kits for race operations. Car and Driver even had a brief mention of the "dry" properties of nitrogen compared to regular compressed air.

I also submit that a perfectly acceptable reason to use nitrogen fills in your tires is "because that's what the Ferrari F1 team does", as evidenced by this pic I took in the pits at Laguna Seca this summer during the Corsa Clienti race...

Gio P
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Birdman, I'm not a scientist like you, nor do I play one on TV, so I may very well be completely wrong.

What I passed along is, however, widely perceived to be true. Could it all be myth? Possibly. But here are a couple of sources:

TIRE RESEARCH

The following is an excerpt from a research paper prepared by Lawrence Sperberg concerning the use of nitrogen gas for tire inflation.

by Lawrence R. Sperberg

Copyright 1985 & 1996 Lawrence R. Sperberg, Probe Forensic and Testing Laboratory, El Paso, Texas. All rights reserved.

All pneumatic tires have suffered from a deterioration starting the day that tires were invented. That deterioration is chemical oxidation masquerading under the name of "tire fatigue".

THE ENEMY - OXIDATION

Causing the deterioration are oxygen molecules contained in the inflating air which is a mixture of gases - nitrogen 78%, oxygen 21%, argon 0.9%, and miscellaneous O.1%. Tires are designed to be protected from this deterioration by their liners which are supposed to keep air from percolating through them into the tire body, which they never do, and by chemicals called antioxidants or age resisters whose job is to intercept and neutralize any invading oxygen - which they do until they are themselves used up, which occurs too soon after a tire enters into service.

So the deterioration spreads. It starts within the tire interior and moves outward. it first invades and consumes the tire liner. It then ravages the insulation rubber adjacent the liner. It marches inexorably outward - because of the pressure differential of the tire inflation on the inside and the atmospheric pressure on the outside. As the decay moves ever outward - the oxygen molecules react chemically with the unsaturated double valence bonds present in all rubbers, causing the rubber molecules to lose their strength and their elasticity, so that they no longer act as rubbers, but instead take on the characteristics of a non rigid plastic. The decay is constantly being fueled by the fresh all too often moist air being injected into the air chamber to maintain the desired inflation pressure.

How do you get a truck tire to go a million miles? It's simple. TAKE THE OXYGEN OUT OF THE AIR!

TRUCK TIRE TESTS

A total of 175 truck tires were tested until they were worn down to the tread wear indicators (TWI). About 125 of these tires wore out without failing at mileages ranging from 125,000 to 225,000. About 50 of the tires failed physically at varying mileages generally on the low side. All the tires had been carefully monitored, measured for tread loss etc., and inspected at 10,000 mile intervals, a lot of them at 2000 to 3000 mile intervals. Tire sizes were mostly 11R24.5 & 11-24.5 with a very few 10R20 and 10-20's. About half of the tires had operated over the eastern part of the United States while the other half had run mostly in the southwestern part of the U.S.

When the tires were removed from service small samples of tread rubber were taken from the shoulders of the unfailed tires and from the actual failed areas of the destructed tires. These specimens were then subjected to the electron microprobe examination that has been described previously. The examination was specifically directed at determining oxygen and sulfur levels which was best accomplished by using IOKV (10000 electron volts) electron beam And an exposure of 30 seconds.

Both of the figures tell the same story. When a tire lives to wear out, the oxygen slowly migrates and permeates its way into and through the tire cord body and finally into the under tread and then into the tread itself. It takes a long time for an appreciable amount of oxygen to reach the tread since most of the oxygen gets waylaid along the way by the liner, and then the cord arid cord insulation compound.

One reason that truck tires can run 250,000 miles with the original tread while passenger tires can only go 50 to 60,000 miles lies in the relative bulk of the 2 different tire bodies. The bulkier the body the longer it takes for the oxygen to work its way into the tread. Unfortunately the bulkier the body the higher is the heat buildup and the faster is the rate of oxidation of the available double bonds. Once the tire body is all oxidized the tire is dead no matter how much tread remains on it. The thinner the tire body the lower the running temperature and the slower the rate of oxidation with a correspondingly longer life.

Practically all tire engineers throughout this century attribute the gradual loss in tire strength to be the result of "fatigue" when in reality this "fatigue" is nothing more than a slow inexorable oxidation taking place at the available double bonds of the rubber molecules.

IMPROVED TIRE LIFE

In one experiment involving 54 new 10.00-20 truck tires, 33 were inflated with nitrogen and 21 were inflated with air. These tires were run side by side on the same tractor units until they failed or until they wore to the tread wear indicators. In this case the 54 new truck tires, nitrogen inflation resulted in 26% more miles being run before tires had to be removed when wear reached the tread wear indicators.

In the case of the failed tires a smaller percent of nitrogen tires failed physically (30% vs. 57%) and they gave 48% more miles before failing than did the air tires. This 48% improvement is due to the tire bodies lasting longer and not the better wearing properties of the tread which is the situation with the tires that lived to wear out.

The experiments involving 54 new and 44 used tires running some 7,345,497 tire miles in drive axle service, when viewed in light of the election microprobe experimental findings presented earlier, depict a clear cut picture of what nitrogen inflation can do for the transportation industry - cost wise as well as safety wise.

HOLDING PRESSURE BETTER

Today probably 99% of all tires are tubeless - truck, passenger, giant - and these tires are inflated with air, and all too frequently with wet air, i.e. air where the water has not been drained from the compressor tank as it should be. This moisture laden air (oxygen catalyzed by water) attacks the paint in the wheel well ultimately penetrating the paint and oxidizing the iron below it to form iron oxide or rust. Even aluminum is not immune from rusting, forming aluminum hydroxide, that gives an extremely fine dust that is difficult to even see inside the tire. The iron oxide rust is present within the tire in varying sizes ranging from coarse to extremely fine. Aluminum hydroxide dust is never coarse only extremely fine.

Whenever a tire is checked for its inflation pressure the pressure gauge requires a small gulp of air to activate the gauge. When the small gulp of air escapes from the tire the turbulence created picks up the finely divided rust and the dust enriched gulp of air passes around the open valve core which has been opened by the tire gauge. When the valve core drops backward into place after the gauge is removed some of the tiny rust particles get trapped between the rubber or plastic seal and the metal housing surrounding the seal.

This results in an extremely slow air leak that all too often escapes detection by the person gauging the tire and unless a metal valve cap which has another sealing surface in it is screwed onto the valve stem the tire will continue to lose air, albeit very slowly. When a larger rust particle is trapped between the core and housing, the escaping air is easily recognized so that proper action can then be taken immediately to correct the problem.

The perennial problem of low tire inflation can be effectively solved by the simple expedient of using nitrogen to inflate tires. Nitrogen is dry and contains no moisture. Nitrogen is inert so rust cannot form since there is neither oxygen nor moisture present to cause oxidation of the wheel.
__________

www.retread.org/PDF/RAv8i3NitrogenArticle.pdf

__________

Take all of this with a grain of salt. I use regular, ordinary, free air, on all my cars, street and track. I just check them regularly and not worry about it.

vty,

--Dennis

 

Birdman, as always you amaze with your vast knowledge! Regarding thermal conductivity:
Argon 0.016 (W/m.k)
Nitrogen 0.024 (W/m.k)
Air 0.024 (W/m.k)
We use argon as our inert process gas in our high temperature(2000+C) vacuum systems. Nitrogen has too many inherent problems at that temperature. John.
PS. Email directions or your address if convenient. I will visit Monday to see Verell and yourself if I can escape Christmas family obligations! Will even bring the valve tool in case you change your mind!

 

62 last night @ ~ 8:00PM in Tallahassee...we did have a little rain however...

 

-10 at Noon in Fargo today. Thankfully no wind.

 

Dennis,
That's an interesting paper by Sperberg. What I like most about it is that it confirms what I said in my first post in this thread!

I'd be willing to bet that the advantages of nitrogen in tires are that it is dry and contains no oxygen. It could be just about gas, as long as it was dry and didn't have O2 in it! If you could keep it in there without it leaking out, I'll bet Helium would be even better, Much better thermal conductivity than nitrogen.

Spider, I'll send you directions! See ya then! Maybe Doody will swing by too.

Birdman