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nitrogen??


lubie

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Being a long time car repair guy, i know several who run nitrogen in their tires. They claim much better tire life. So, since i just mounted a set of BT020's on my wife's R1150R, i filled them with nitrogen, then took my R1200RT and had them done. A friend of mine is worried that the tires won't heat up enough to grip well during fast corners. I don't ride anywhere near the limit cuz I'm too old and it hurts the body and the wallet, so I don't see a problem. Anybody have some experience with this??

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Personal opinion, nitrogen in street tires (only anything) is just the latest marketing gimmick. Plain old air is already 85% nitrogen anyway.

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In the "Downtime Files" section of the Oct. 2006 Motorcycle Consumer News, a reader asked about the benifits of nitrogen as opposed to air.

 

1. The process for recovering nitrogen from air produces a dry gas(no water vapor). The water vapor in air, will expand at a greater rate than either oxygen or nitrogen. Racing bike(and car) tires are filled with nitrogen to reduce pressure changes as the tire heats up.

 

2. Nitrogen will leak more slowly through tire body than air (1/6 as fast).

 

3. The oxygen(and water vapor) in air will oxydize both tire and wheel components; nitrogen won't.

 

It's also pointed out that even if you fill your tires with nitrogen, there will still be ambient air in the tire prior to pumping up the tire.

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ShovelStrokeEd

1. The pressure change due to water vapor in the air is trivial. Liquid water, as in mist rather than vapor, will cause a much larger pressure change. Mitch put paid to this quite a while ago.

 

2. Nitrogen molecules are larger than Oxygen molecules (most of the rest of air) and thus will diffuse more slowly but, the difference would not be measurable with common tire pressure gauges over the course of even months.

 

3. Again, the tire is going to break down anyway as ozone from the surrounding atmosphere will get to it faster than the oxygen in the air inside it. The process would take years and most of us go through a set of tires in less than that. I'm lucky to get 4 months out of a set.

 

In short, there is little or no benefit on a street driven vehicle to using N2 in the tires. Their rubber is already compounded to resist the chemical reactions. A race tire, whose useful life is measured in minutes rather than months has no such protection but, the reaction takes a lot longer than the 50 or so laps it will be on the vehicle.

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For the record, I didn't buy in to the what the article was suggesting. I've never had a set of tires wear-out from the inside.

 

Filling tires with nitrogen would seem to make more sense when a car is to be sitting around for a very long time; like in a museum or in storage.

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Joe Frickin' Friday

I've been waiting for someone to ask this question. crazy.gif

 

A lot of companies are offering to fill your tires with nitrogen – for a price. Or they talk up the benefits of nitrogen, and then offer a free fill if you buy tires from them. But is nitrogen really that much better than air for tires? I spent a fair amount of time recently digging into the issue, examining the various claims, and trying to determine whether the benefits offered in one venue (say, racing or aerospace) also exist for the average consumer’s automobile or motorcycle.

 

The sad fact is that I couldn’t find many good, unbiased technical documents on the subject of nitrogen as a tire fill gas. So what follows is my own engineering analysis, bolstered in places by technical references that address specific aspects of the behavior of nitrogen, oxygen, and air. Each claim that I’ve heard about nitrogen as a tire-fill gas is stated as a red, bolded, underlined question, followed by my own long-winded answer. Here we go:

 

Does a tire filled with dry nitrogen have a more consistent pressure?

Some folks have asserted that racers use dry nitrogen in their tires because the pressure of nitrogen varies (with temperature) less than air, or less than moist air, or more predictably than some random mixture of air and water vapor. With the aid of some thermodynamic software, I decided to see just how tire pressure varies over a range of temperatures for different gas mixtures.

 

If you only want to see the case studies and understand what is happening when a tire is filled with different gas mixtures, skip ahead to the Case Study section. If you are interested in understanding why different tire fills behave differently, keep reading.

 

Before we get rolling, I need to explain some terms and concepts that are used in discussions of gas pressure. Engineers and chemists will already understand this stuff, but other folks may appreciate the following information.

 

”Gauge” and “Absolute” Pressure

When we measure tire pressure with an ordinary tire gauge, we are measuring “gauge” tire pressure. This is the difference between the pressure inside the tire and the ambient (atmospheric) pressure. So at sea level, where atmospheric pressure is 14.7 psi, if you measure your tire to be at 40 psi-gauge, it’s actually at 54.7 psi-absolute. If you get a flat and measure 0 psi-gauge, your tire still actually has 14.7 psi-absolute in it. This is why the gauge-pressure in your tires actually increases when you ride to high elevations: at the top of Loveland Pass (11,000 feet), atmospheric pressure is only 9.8 psi, so your tires, which were 40 psi-gauge at sea level, are now at 44.9 psi-gauge, but their absolute pressure is still 54.7 psi; this is even before considering any temperature differences. Most people will only ever deal with gauge-pressure, but in engineering analyses – particularly when dealing with pressure ratios and assessments of gas behaviors – absolute-pressure measurements are important.

 

Partial Pressure

The total pressure of a mixture of gases can be understood as the sum of the partial pressures exerted by each component gas. For example, in the atmosphere (by volume: 78% nitrogen, 21% oxygen, 1% other stuff), the total pressure is 14.7 psi at sea level; the partial pressure of nitrogen is about 11.5 psi; and the partial pressure of oxygen is about 3.1 psi. The great thing about this is that in a mixture of gases, you can analyze the pressure behavior of each component gas independently of whatever other gases are there. If I have a container full of neon at 100 psi, and I add helium until the total pressure in the container is 200 psi, the partial pressure of the neon is still 100 psi. This idea will come in handy later when trying to understand the behavior of water vapor in a tire full of moisture-laden air.

 

Vapor Pressure

Every substance has a property called vapor pressure. If you have an exposed liquid surface, the substance will continue to evaporate until the partial pressure of that vapor reaches the vapor pressure for that substance. At that point, no more liquid will evaporate, and if the system is cooled, some of the substance will condense back into liquid. Note that this behavior is entirely independent of whatever other gases might be present. So the vapor pressure of a substance is the maximum possible pressure at which that substance will remain in a gaseous state. As the temperature is increased, the vapor pressure also increases, as in this plot:

 

(click on plot for larger version)

water-small.jpg

 

Note that at 212 degrees F, the vapor pressure of water is 14.7 psi; this is the temperature at which water boils (at sea level).

 

A practical example:

At 70 degrees F, the vapor pressure of water is 0.363 psi. A mixture of air and water vapor at 70F in which the partial pressure of water is 0.363 psi is said to be at 100 percent relative humidity. A bowl of liquid water left out in this environment will not evaporate at all, and if this moist air is cooled off even slightly, fog (suspended droplets of liquid water) will form.

 

Again, note that this behavior of water vapor is independent of whatever other gases might be present, no matter the total pressure.

 

Another practical example:

Run a compressor on a day with 100% relative humidity, and fill a storage tank to 150 psi-gauge (164.7 psi-absolute). In addition to compressing the air, you’ve also compressed the included water vapor. The total pressure increased by a ratio of 164.7/14.7 = 11.2, so the partial pressure of the water vapor has been increased to 0.363 * 11.2 = 4.1 psi. Compressing the air also heats it up a lot, so that water remains in a vapor state. However, the air eventually cools down to 70F; when it does, water vapor will condense on the inside of the tank until the partial pressure of the remaining water vapor drops to – you guessed it – 0.363 psi. (This is why you have to drain condensate from the tank on a regular basis.)

 

Now take that air and let it back out to the atmosphere; the expansion results in a water vapor partial pressure of 0.363/11.2 = 0.0324 psi. The expansion will initially cool this mixture off, but after it warms back up to 70 F – where the vapor pressure of water is 0.363 psi – the relative humidity will be 0.0324/0.363 = 8.9 percent. What this means is that filling your tires from a high-pressure storage tank is the equivalent of filling it directly with ambient air at 8.9% relative humidity.

 

Some compressors don’t have a storage tank. Most notable among these are the little ones you carry on your bike so that you can repair a flat tire by the side of the road. In this case, you can regard your tire as the storage tank: you squeeze moist air into the tire, and as was just described, unless it’s a very dry day some of the moisture is guaranteed to condense into liquid in there. Won’t be quite as much, since you only fill your tire to about 40 psi instead of 150 psi, but you get the idea.

 

Now that we all perfectly understand gauge/absolute pressure, vapor pressure, and partial pressure, let’s move on to the case studies.

 

Case Studies

I simulated six different tire fills. In all cases, the tire begins at 70 degrees F, 40.0 psi (gauge). The cases differ only as follows:

 

  • Case #1: You carefully and sparingly apply lubricant only to the contact zones of your tire bead, and mount your tire on the rim. From a tank of dry compressed air, you fill your tire and purge it a couple of times to get rid of most of the atmospheric air that was in there just after you mounted it. When you’re done, you’ve got a tire filled to 40 psi with dry air, no moisture whatsoever.
     
     
  • Case #2: You carefully and sparingly apply lubricant only to the contact zones of your tire bead, and mount your tire on the rim. From a tank of dry compressed nitrogen, you fill your tire and purge it a couple of times to get rid of most of the atmospheric air that was in there just after you mounted it. When you’re done, you’ve got a tire filled to 40 psi with dry nitrogen, no moisture whatsoever.
     
     
  • Case #3: You carefully and sparingly apply lubricant only to the contact zones of your tire bead, and mount your tire on the rim. You have a compressor in your garage with a large tank which you maintain at 150 psi. From this you fill your tire and purge it a couple of times to get rid of most of the atmospheric air that was in there just after you mounted it. When you’re done, you’ve got a tire filled to 40 psi with slightly moist air.
     
     
  • Case #4: You carefully and sparingly apply lubricant only to the contact zones of your tire bead, and mount your tire. It’s a comfortable day, 70 degrees F and 50% relative humidity. You have a cigarette-lighter-powered compressor – no storage tank – that takes that moist atmospheric air and stuffs it directly into the tire. When you’re done, you’ve got a tire filled to 40 psi with moist air and a small amount of condensate.
     
     
  • Case #5: You carefully and sparingly apply lubricant only to the contact zones of your tire bead, and mount your tire. It’s a muggy day, 70 degrees F and 100% relative humidity. You have a cigarette-lighter-powered compressor – no storage tank – that takes that moist atmospheric air and stuffs it directly into the tire. When you’re done, you’ve got a tire filled to 40 psi with moist air and a slightly larger amount of condensate.
     
     
  • Case #6: You sloppily ladle on a gross excess of tire lube, leaving a small puddle of the stuff inside the tire. You fill the tire to 40 psi, and when you’re done there’s still a puddle of liquid water in the tire.

 

 

 

Results

Here’s an overview of what happens to tire pressure over a very wide range of temperatures:

 

(click on the plot for larger version)

overview-small.jpg

 

As was explained, all six cases are set up so that at 70F, they are at 40 psi.

 

As the temperature drops below 70F, the water vapor in cases #4, 5, and 6 condenses, lowering the water vapor partial pressure and causing these cases to deviate from cases #1, 2, and 3 – but not by much, only about 1/3 of a psi as you approach 0F. In fact, the deviation will never exceed 0.363 psi, and that extreme will only happen if you somehow manage to get all of the water vapor to condense out (for example by cooling to cryogenic temperatures). In case #3, the amount of water vapor is so small that you don’t actually get any condensation until about 40F.

 

As the temperature climbs above 70F, case #6 climbs steeply, especially when we get well past 100F. The puddle of water in the tire adds more and more water vapor to the gas mixture as the temperature increases. In the theoretical extreme tire temperature of 212F, the partial pressure of the water vapor would be 14.7 psi, resulting in a huge discrepancy between case #6 and all the others.

 

OK, so now we’ve seen what happens in the extreme temperature limits. What happens in the normal operating range of a typical motorcycle tire? Here’s a detail plot of tire pressure behavior within the range where it’s likely to operate most of the time, i.e. start at 70F, and work that tire until it’s somewhere around 110F-120F:

 

(click on the plot for larger version)

detail-small.jpg

 

The first thing to notice is that throughout the entire operating range of the tire, cases #1, 2, and 3 are virtually identical, differing by no more than 0.04 psi at 110F. In other words, it doesn’t matter whether you’re using desiccated-dry air, air from a 150-psi storage tank, or dry nitrogen: all three mixtures respond the same, with negligible difference, to temperature changes.

 

The rule of thumb one often hears is that the cold tire pressure should be set so that when the tire warms up during the normal course of riding, the pressure increases by about 10 percent; for this study then, we’re talking about an increase of 4 psi. Note that for cases #1, 2, and 3, this corresponds to a final gas temperature of about 109F (though the tread may be significantly warmer than this). At this temperature, case #4 pressure has risen (from cold) by 10.8 percent (an extra 0.3 psi), and cases #5 and 6 have risen by 12.2 percent (an extra 0.8 psi). For a typical motorcycle front tire, if you take the water vapor present in cases #5 and #6 at 109F and condense it down to liquid form, it’s a cube of liquid water 5/16” on a side – about 2/3 of a gram. In other words: no matter what you fill your tire with, if you (or your tire-mounting mechanic) got even SLIGHTLY sloppy with the tire bead lube when you mounted your tire, it’s going to behave like case #5 or 6.

 

So the bottom line on temperature versus pressure: if you’re sloppy with the lube when mounting the tire on the rim, it won’t matter what you fill with. And even if you’re fastidious about using just enough lube to get the job done, it doesn’t matter whether you fill with nitrogen, dry air, or compressed atmospheric air from a high-pressure storage tank: they all behave the same way.

 

Now that we’ve dealt with the whole pressure-versus-temperature thing, let’s check out some of the other assertions that are frequently made regarding nitrogen in tires.

 

 

 

Do nitrogen-filled tires run cooler?

IF it’s true that N2-filled tires lose pressure more slowly – AND if you’re a slacker either way when it comes to checking pressure – then yes, your tires will run cooler on nitrogen, simply by virtue of being inflated correctly more of the time. But there is not a significant difference in the thermal properties of nitrogen and air, and in the worst case, water vapor (with similar thermal properties) will only make up about 1% of the fill mixture. So when it comes to transporting heat from the tire to the rim, the difference between air (whether wet or dry) and nitrogen is negligible. A tire filled with pure nitrogen to X psi will run at the same temperature as a tire filled with air (wet or dry) to X psi.

 

 

 

Do nitrogen-filled tires deliver better fuel economy?

IF it’s true that N2-filled tires lose pressure more slowly – AND if you’re a slacker either way when it comes to checking pressure – then yes, your tires will deliver better fuel economy on nitrogen, simply by virtue of being inflated correctly more of the time. But there is nothing about the chemical properties of nitrogen that cause it to imbue a tire with lower rolling resistance than air. A tire filled with pure nitrogen to X psi will deliver the same fuel economy as a tire filled with air (wet or dry) to X psi. If it actually did make a difference, car manufacturers – always desperate for ways to increase fuel economy – would specify it in the owner’s manual.

 

 

 

Do nitrogen-filled tires lose pressure more slowly?

This seems to be the main selling point for nitrogen vendors, i.e. you don’t have to check/top-off your tire pressures as frequently as you do with air. N2 vendors claim that N2 leaks out anywhere from 3 to 6 times slower than air. This is amazing, since air is about 78% nitrogen.

 

But then again, there may be something to it. I’m aware of two techniques for separating nitrogen and oxygen from atmospheric air. One is cryogenic: you literally cool the air down until the oxygen condenses into a liquid, while the nitrogen remains a gas. The other technique is membrane technology, explained here. Interestingly enough, this is one of the ways that tire shops obtain nitrogen: they run compressed air through an on-site membrane tube bank (click here, see page 4). The only way this technology works is if O2 permeates through a polymer membrane a lot faster than N2 does. Molecule size is one factor (N2, atomic radius = 75 pm, diatomic bond length = 110 pm; O2, atomic radius = 66 pm, diatomic bond length = 121 pm), but the physics of permeation seem to be considerably more complex. Click here for a more in-depth explanation, and take a look in particular at Table 1 to see how oxygen and nitrogen permeate differently through different materials; note how the selectivity (the ratio of O2 and N2 permeation rates) varies by material, indicating that molecule size isn’t the only factor at play.

 

This source offers permeation coefficients for still other materials. Check the bottom of the first table, where we see values describing the diffusion of four common gases through butyl rubber, a material with relatively low O2 and N2 permeability that’s commonly used for inner tubes and as the inner liner on tubeless tires. Of particular interest are the values shown in the far right column, expressed in grams per meter per second. They show that for oxygen and nitrogen under the same pressure, oxygen diffuses through butyl rubber at 4.66 times the rate of nitrogen, i.e. the O2/N2 selectivity is 4.66 (on a mass basis; on a volume basis, it’s 4.08). However, for air, the partial pressure of O2 is far less than that of N2. Using the values in that table, we can go through some basic algebra to come up with an estimate of the relative leakage rates for air and pure nitrogen:

 

Suppose we have a tire filled to X psi with pure nitrogen, and we define the leakage rate as “1”. Now we estimate what the relative leakage rate would be for the same tire filled with air. Using air, the partial pressure of nitrogen would be 0.78X, so the relative leakage rate of the nitrogen from that air-filled tire would be 0.78. The partial pressure of oxygen in that tire would be 0.21X, much lower than that of the nitrogen. However, the oxygen’s propensity for diffusion is 4.08 times (on a volume basis) that of nitrogen; the combined result is that the oxygen portion of that air-fill diffuses out at 0.21 * 4.08 = 0.857 times the rate of the nitrogen-filled tire. With nitrogen and oxygen both leaking out of the air-filled tire at the same time, the total leakage rate is approximately 0.78 + 0.857 = 1.637 times that of the nitrogen-filled tire. This is considerably less than the “3 to 6 times faster” that some tire stores (like Belle Tire) claim, but it’s not far off from Ingersoll-Rand’s claim that oxygen - not air - leaks out 3 times faster than N2. (Interestingly enough, even IR can’t keep their facts straight: over here, they claim that O2 leaks out only 30-40 percent faster than N2. Probably an editing error, since the previous assertion – 3X – is in closer agreement with the O2/N2 selectivity I found from the other source.)

 

OK, so someway, somehow, it seems that air DOES sneak through a tire faster than pure nitrogen; go figure. But is it worth the extra expense/hassle of using nitrogen instead of air? If you operate a trucking fleet and each of your drivers spends half an hour every two weeks checking/topping off his truck’s eighteen tires, then yeah, it may be worth it to buy/use a nitrogen generator and cut that tire-checking by 40%. Me? I’m still checking my RT’s tires before every ride, whether they leak down slowly or not; regular checks can help you catch small leaks before they become a big problem (e.g. 50 miles from home).

 

Note also that if you fill and top off with air, the percentage of N2 will gradually increase over time; at first you lose about half O2 and half N2, but you top off with a mixture of 78% N2 and 22% O2. So if you fill your tires with air and they initially lose about a psi a month, then after a year of this, it’s down to mostly N2 inside the tire, and the leakdown rate should slow down. For most folks here, motorcycle tires don’t make it through a season before replacement, so the effect is negligible; but if your car tires last four years, then by using air in them you’ve actually gotten about 3/4 of the benefit of a N2 fill, without the expense. cool.gif

 

 

 

Do nitrogen-filled tires eliminate tire oxidation/aging?

Oxidation damage will be related to the partial pressure of oxygen inside the tire, as well as to the time spent at elevated temperatures. On a commercial aircraft tire filled to around 200 psi, if air was used the O2 partial pressure would be 42 psi. With the heat generated from braking during landings, the use of nitrogen on aircraft tires has more to do with eliminating fire/explosion hazards than it does with preventing tire aging. Likewise with the space shuttle, whose tires are filled with nitrogen to 315 psi, and get replaced after every single landing; clearly NASA is not interested in nitrogen for the purpose of extending tire life. (if you want to see what crazy things can happen in an oxygen-rich environment, read up on Apollo 1. Also, for more information on the matter from a purported aircraft mechanic, click here and check out comment #2.)

 

Truck tires filled to 100 psi still have a moderately high PP of O2, and they get retreaded multiple times in an effort to get upwards of 250K miles out of them; under those circumstances, it’s important to minimize aging and embrittlement of that carcass material, so there may be an advantage for these guys.

 

For a car tire operating at 40 psi that’s going to last maybe 50K miles before being discarded, tire carcass oxidation is a non-issue. When you hear of instances of automotive tire failure, it’s almost always related to underinflation, road damage, or a pre-existing defect; very, very rarely is it related to carcass oxidation.

 

And for a bike tire that’s going to last between 3K and 10K miles? Same thing: my worn-out tires are always in beautiful condition (on the inside).

 

 

 

Do nitrogen-filled tires eliminate rim oxidation/damage?

The partial pressure of oxygen comes into play again, as does the presence of moisture, and the susceptibility of the rim material to oxidation. Aluminum tends to form a protective oxide coating that inhibits further oxidation; this is generally not true of steel, which (if the paint somehow gets damaged) will rust and then flake away to expose underlying metal. Most truck rims are steel (and at 100 psi have a high pp of O2), and are expected to travel many hundreds of thousands of miles, so nitrogen may offer benefits if the rim’s paint is compromised. On a car or bike operated at 40 psi, the pp of O2 is lower; they’re usually aluminum rims; and most folks sell the car or bike before it hits 100K miles. I change my own bike tires, and after 110K+ miles, I haven’t seen any signs of rim corrosion.

 

 

 

Do nitrogen-filled tires eliminate crud that might otherwise keep the valve from sealing properly?

If you’ve got a steel rim in rough shape with lots of rust and crud bouncing around inside the tire, it’s conceivable that you could get a tiny piece that at some point lands at the base of the valve stem and gets blasted into the valve’s sealing area next time you check the pressure. But that’s a filling valve, and you’re not supposed to be relying on it for long-term sealing; this is what valve caps are for. Goodyear is pretty specific about valve caps, going so far as to specify metal valve caps for high pressure aircraft tires (click here, see page 24).

 

 

 

 

So, for the average car/bike owner…nitrogen or air?

If you’re a slacker when it comes to checking tire pressures (or using valve stem caps), then nitrogen may be just the thing for you; decide for yourself whether the time you save in pressure-checking justifies the extra cost of using nitrogen. But if you’re as vigilant as you ought to be about vehicle maintenance/inspection, then here’s what you can expect:

 

  • fuel economy: no difference.
     
  • Pressure-versus-temperature behavior: no difference, unless the air you’re using came straight from the atmosphere on an extremely humid day.
     
  • tire operating temperature: no difference.
     
  • Tire oxidation/aging/failure: no difference.
     
  • Leaky valves: no difference.
     
  • rim oxidation/corrosion: no difference.

 

In fact, according to this article, “Michelin officials recommend nitrogen only for tires used ‘in a high risk environment and/or when the user wants to reduce the consequences of a potential abnormal overheating of the tire-wheel assembly (for example in some aircraft applications),’ according to a company statement.” IOW, the average Joe should save his hard-earned money and just inflate his tires with air.

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And I thought it would be just another boring lunch hour..... crazy.gifdopeslap.giflmao.gif

 

Also, I can add just a small bit of confirmation to a bit of Mitch's information. Having worked for one of the main tire valve suppliers in the United States, I can vouch for the fact that the single most important seal in a tire valve is the valve cap. In the industry, it is refered to as the "Primary seal". If you knew how the valve is really made, you would most definitely agree with this. smile.gif

 

Shawn

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IOW, the average Joe should save his hard-earned money and just inflate his tires with air.

 

Mitch, could you elaborate on the idea of who fits the definition of an "average Joe"? My mother always told me I was above average, but most standardized measurement tests do not agree. eek.gif

 

Seriously, that was a great explanation. You should submit that for publication. Maybe BMW Owners News?

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Joe Frickin' Friday
IOW, the average Joe should save his hard-earned money and just inflate his tires with air.

 

Mitch, could you elaborate on the idea of who fits the definition of an "average Joe"?

 

Basically, if you don't have Ralph Schumacher or Burt Rutan on speed-dial, you're an average Joe. crazy.gif

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quote-For the record, I didn't buy in to the what the article was suggesting. I've never had a set of tires wear-out from the inside.

 

-Sometimes they will-if the compressor that fills them is bypassing oil,they'll rot from the inside.

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Very impressive. Thank you very much. Could you do a wright up on fuel. With octane ratings and all that.

I know I'm getting greedy, grin.gif but that was fabulous.

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Hey Mitch....here we go again another N2 thread..... eek.gif didn't someone find little round balls of hardened rubber sphere's between the rim and tire internal carcass using this proclaimed wonderful element for replacement of 02. grin.gif

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Joe Frickin' Friday
Hey Mitch....here we go again another N2 thread..... eek.gif

 

Yep! And I'm saving what I wrote so I can post it again whenever anyone asks the nitrogen question. wave.gifcrazy.gif

 

didn't someone find little round balls of hardened rubber sphere's between the rim and tire internal carcass using this proclaimed wonderful element for replacement of 02. grin.gif

 

I had those little rubber BB's, but I wasn't using N2, just plain 'ol air. Not sure how they formed, whether air (instead of nitrogen) had anything to do with it or not. Would guess I just got stupid-sloppy with the tire lube and the residue peeled off and formed little marbles. Only ever saw it once in all my tire changes.

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And I'm saving what I wrote so I can post it again whenever anyone asks the nitrogen question.
And now if you could just do the same thing for oil selection and tire repair we'd be cookin'...
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If somebody were really interested in preserving the insides of their tires, helium would make much more sense than nitrogen.

 

It's chemically inert, and it conducts heat much better than air.

 

On top of that, it would reduce your unsprung weight.

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  • 10 months later...

Water vapor has about 100 times the permeability of nitrogen in butyl rubber. This results in the combined permeability of "air" (N2 + O2 + Ar + water) being about 3 x that of dry "nitrogen" (95% N2, balance O2/Ar). As a result, the oxygen content in the tire isn't decreasing as fast as some have suggested.

 

The other factor is chemical reactivity. Both water and oxygen, in the presence of moderate tread temperatures (tires flexing/unflexing 10 to 15 times a second), act to slowly degrade ("unzip") the polymer chains that make up rubber. The absence of water/oxygen help to significantly prolong life.

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The other factor is chemical reactivity. Both water and oxygen, in the presence of moderate tread temperatures (tires flexing/unflexing 10 to 15 times a second), act to slowly degrade ("unzip") the polymer chains that make up rubber. The absence of water/oxygen help to significantly prolong life.
Hands up all those whose tyres have worn out from the inside before the outside?
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I saw some of those bb's in a tire I just changed for a friend...my theory is some piece of sand (small pebble?) that has been spinning aroud inside the tire for 5 or 6K just slowly gets wrapped in rubber (like a snowball rolling down a hill)....

 

Nice job on the nitrogen write up....you PhD's types really do have a gift for making a simple concept seem complex... smile.gif

 

I'll stick with plain old air, my tires wear out on the outside faster than any oxygen related interior wear can hope to keep up with...

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Hydrogen is even better for heat transfer. Actually nothing is better thatn hydorgen. Which is why all large alternators (power plant size Hundreds to thousands of megawatts) use a supersaturated hydrogen vapor as a coolant. As long as you keep the O2 away no boom.

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Water vapor has about 100 times the permeability of nitrogen in butyl rubber. This results in the combined permeability of "air" (N2 + O2 + Ar + water) being about 3 x that of dry "nitrogen" (95% N2, balance O2/Ar). As a result, the oxygen content in the tire isn't decreasing as fast as some have suggested.

 

The other factor is chemical reactivity. Both water and oxygen, in the presence of moderate tread temperatures (tires flexing/unflexing 10 to 15 times a second), act to slowly degrade ("unzip") the polymer chains that make up rubber. The absence of water/oxygen help to significantly prolong life.

 

Interesting first post and welcome.

 

If your statement is correct, does it have any real world application to m/c tires that most of us wear out in a short period of time? This slow "unzipping" takes how long to have a measurable effect?

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Wouldn't want to even attempt to add anything to the scientific tour de force above, but it seems to me the only real-world advantage of nitrogen for tyre inflation is that all you need's a bottle of it, a valve and suitable connector for the tyre valve. No compressors, electrics, or farting about with bits and pieces. There may be times when that simplicity would be welcome - racing, for instance.

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Wouldn't want to even attempt to add anything to the scientific tour de force above, but it seems to me the only real-world advantage of nitrogen for tyre inflation is that all you need's a bottle of it, a valve and suitable connector for the tyre valve. No compressors, electrics, or farting about with bits and pieces. There may be times when that simplicity would be welcome - racing, for instance.
How is that not true of air?
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Mitch, would you be kind enough to run all those numbers against helium? I heard somewhere on the internet that the reduced weight of helium offsets the benefits of nitrogen.

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Joe Frickin' Friday
Wouldn't want to even attempt to add anything to the scientific tour de force above, but it seems to me the only real-world advantage of nitrogen for tyre inflation is that all you need's a bottle of it, a valve and suitable connector for the tyre valve. No compressors, electrics, or farting about with bits and pieces. There may be times when that simplicity would be welcome - racing, for instance.
How is that not true of air?

 

I haven't checked, but I'd speculate that bottled N2, being a byproduct of the O2 liquification process, is cheaper than bottled air.

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Joe Frickin' Friday
Mitch, would you be kind enough to run all those numbers against helium? I heard somewhere on the internet that the reduced weight of helium offsets the benefits of nitrogen.

 

confused.gif

 

For a pair of moto tires at 42 psi, the total vehicle weight savings (He vs N2) is about a 1/4 pound. Not much weight savings, and He is expensive, hard to find, and leaks out pretty fast.

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Mitch, would you be kind enough to run all those numbers against helium? I heard somewhere on the internet that the reduced weight of helium offsets the benefits of nitrogen.

 

confused.gif

 

For a pair of moto tires at 42 psi, the total vehicle weight savings (He vs N2) is about a 1/4 pound. Not much weight savings, and He is expensive, hard to find, and leaks out pretty fast.

 

Gotcha! lmao.gif

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How is that not true of air?

 

It isn't not true of air, if you'll forgive the tortured English. But given that the discussion was about nitrogen.......... eek.gif

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ShovelStrokeEd

I haven't checked, but I'd speculate that bottled N2, being a byproduct of the O2 liquification process, is cheaper than bottled air.

 

True dat.

I keep a small tank of N2 in my garage for topping up tires and the like. I also have a big one. The small tank is $11 to fill with N2, $14 with air. I haven't run the big tank down yet so can't quote a price. I really only use it when I need an air tool and don't use them much on bikes.

 

I have the small tank left over from my drag racing days. It was a lot easier to chuck it into the trailer than the big one. Have a fixed pressure regulator on it set at 150 PSI cause that's what I ran in my air shifter.

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I just ordered a set of Bridgestone 020 tires and asked if they could ship new tires in pickling air so no regular air will come in contact with my tires, Then I am going to mount my tires inside a vacuum chamber so I can make sure only 100% Nitrogen is used to service tires. One can't be to careful.

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Hands up all those whose tyres have worn out from the inside before the outside?
Ah-ha! That explains the guy in the other thread who is getting 30K - 45K out of a set of tires on his RT! He's running them inside out! lmao.gif
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