While this is primarily an anthropology and archaeology blog, I also like to write about skeptical topics as well. I’ve written several bits about pseduoarchaeology in the past, but this topic is a straight bit of skepticism.
My wife and I recently traded in one of our 2000 model Saturns for a new 4-cylinder Ford. Having sold new cars for a living about 8 years ago (that’s how we ended up with two Saturns!), my wife knows the car business and wasn’t about to let anyone sell her any add-ons, after market B.S., extended warranties, and all the other sorts of insurance the dealers really make a fair bit of money on. Indeed they were completely frustrated that she and I wouldn’t even bat an eye at what they had to offer.
But, when the finance manager went into his pitch on Nitrofill. This is essentially a service they provide to periodically fill the tires with nitrogen instead of normally compressed air. The difference, he stated, is that “nitrogen filled tires don’t loose pressure as fast as air and nitrogen doesn’t oxidize the inside of the tire as fast.”
I looked at my wife and saw a bit of hesitation. She was buying it. Literally, if I dindn’t stop her. “Ahem,” I got her attention and she snapped out of it. “Isn’t air already 78% nitrogen?” I asked the finance manager. “Uhh… well I’m not a scientist,” he replied with a sheepish grin. My wife, fully back to her senses smiled broadly, pointed at me and said, “but he is!” I’m not, but having stayed at my share of Holiday Inn Expresses, and having paid some attention in my Chemistry classes, I knew $5.00/tire every time they got low wasn’t an expense I wanted. And, if we filled a tire with air somewhere else, it would be $60 to service the tire and fill it back up with nitrogen. The tire that already had 78% nitrogen.
Needless to say, I we didn’t buy the nitrogen scam. And that’s just what it is. On the surface it sounds good. In fact, if it were free, I’d take pure nitrogen over normal air any day. But I’m not about to let a car dealer or service station sell me the air in my tires.
The claims are this:
- Nitrogen-filled tires maintain proper pressure longer
- The rubber of nitrogen-filled tires last longer
- Nitrogen is less volatile than oxygen and thus safer in a fiery crash
- Cars with Nitrogen-filled tires get better gas mileage
- Cars with Nitrogen-filled tires are better for the environment
The last two claims are dependent upon the expectation that the tires filled with nitrogen are actually at properly inflated pressure more consistently. So let’s set them aside and focus on the first three points.
1. Do nitrogen-filled tires maintain proper pressure longer? The premise for this claim is that nitrogen is a larger molecule than oxygen. It is. Only slightly. But let’s not omit the fact that we’re talking about molecules here and not just the element. Oxygen and nitrogen are both diatomic molecules. Nitrogen actually has less mass than oxygen, so Graham’s Law dictates that it diffuses a bit faster than oxygen. However, since the actual size of the oxygen molecule (O2) is a bit larger than that of a nitrogen molecule (N2), this only applies if the opening from which the molecules are effusing from is large enough to permit the largest of the two. In such cases, N2 will diffuse faster.
The question, then, becomes, are the pores in rubber (assuming there are such pores) smaller than the N2 molecule but larger than the O2 molecule? I don’t know the answer to this. Nor could I find any literature in the few minutes I searched, but if anyone has a citation to an independent (i.e. non Nitrogen Tire industry) study or bit of research, I’m interested. Without digging out my old chemistry textbook, I’m willing to tentatively accept Wiki Answers on the sizes of N2 and O2 molecules: N2 is roughly 300 picometers while O2 is slightly smaller at 292 picometers. I’m open to revising these figures if someone cites a more reliable source, but I can’t imagine that there’d be any reason for the link to be more than slightly wrong.
2. Does rubber oxidize faster when exposed to oxygen rather than pure nitrogen? I’d expect so. The real questions are: a) how to you keep oxygen on the outside of your tires from causing oxidation?, and b) does it really matter to me since every single tire I’ve ever replaced was because of worn tread and not oxidation?
3. Why do I give a shit whether or not the oxygen in my tires will fuel the fire of my fiery crash? If the explosion is powerful enough to consume the oxygen in the surrounding air leaving only my tires as reserve fuel, I suspect I’m going to be a crispy critter anyway.
As for 4. and 5., I’m not that arsed for time that I can’t continue my routine of checking my tire pressure every 3,000 miles when I change my oil. In fact, nearly every time I’ve ever checked my tires at 3k, they’ve either been dead on for the proper psi or just a pound or two off. Whenever I’ve had to fill more than that, it’s been either because of a faulty valve or a nail in the tire itself. I suspect that the resulting points of egress in a faulty valve or pucture would create holes large enough for either O2 or N2 to escape through effusion. So, in that case, Graham’s Law would be in effect and N2 would escape faster than O2.
The bottom line: if nitrogen becomes a free option, easily obtainable (i.e. cheaper and easier than the $5.00 Walmart compressor that I plug into my cigarette lighter), I’ll use it since there’s a very slight chance I won’t need to top off my tire pressure as often. But, as long as I have to pay for it or even just drive to the dealer for it, I call bullshit!
Nitrofill is a scam. Nitrogen-filled tires for general consumers is a scam.
Filed under: Archaeology
Cfeagans
Hello. You may recall that I posted the below entry on your blog, Hot Cup of Joe, countering some of your arguments against nitrogen tire inflation. I was just curious to know why you decided not to publish it? I was always under the impression that the beauty of blogs was that you could often see differing points of view and readers could make their own determination.
Best regards,
John Lucidi
jlucidi@parker.com
First, in an effort to be as forthcoming as possible, I should inform you that I am involved with nitrogen tire inflation. I am a firm believer in nitrogen tire inflation, not only because of the benefits to the consumer, but the environment as well. I run a blog dedicated to nitrogen tire inflation located here:
http://tirenitrogen.typepad.com/tirenitrogen/
Today I came across your blog post about nitrogen tire inflation, and wanted to address a few of your points.
1.) I have no intention of arguing molecular chemistry with you, but will tell you that oxygen permeates through the rubber sidewall of a tire 4-6x faster than nitrogen. If you are looking for non-nitrogen tire market proof, I can direct you to the following reprint from Bridgestone, a major tire manufacturer.
http://tirenitrogen.typepad.com/tirenitrogen/files/BridgestoneReprint.pdf
This is a reprint from their corporate publication Real Questions, Real Answers. I have seen supporting documentation from Ford as well that back up these numbers.
Here are bulletins from Goodyear and Michelin that reference the better pressure retention characteristics of nitrogen inflated tires.
http://tirenitrogen.typepad.com/tirenitrogen/files/goodyear_n2_inflation.pdf
http://tirenitrogen.typepad.com/tirenitrogen/files/goodyear_n2_inflation.pdf
It is a well proven fact within the tire industry that nitrogen inflated tires maintain their pressure better than air filled tires.
2.) You bring up a good point of oxidation of the outside of the casing. As John Baldwin from Ford points out in his paper entitled “Effects of Nitrogen Inflation on Tire Aging and Performance”, chemical aging of the rubber is nearly halted when tires are filled with nitrogen.
http://www.getnitrogen.org/pdf/FordBaldwinResearchRaper.pdf
The reason, no oxygen is permeating through the tire, causing belts to wear and rubber to break down and oxidize internally. By minimizing this internal wear, a nitrogen inflated tire is structurally stronger after 2 years than an air filled tire after 10 weeks (Figure 4).
You will also see, from page 3 of his report, that the Ford Explorer rollovers were partly caused by this issue: “defective in part because the physical properties of rubber in the steel belt area had deteriorated due to oxidative aging.”
3.) Point taken
4 & 5.) NHTSA has stated that 85% of the population does not check their tire pressures regularly and that 30% of cars and light trucks have at least one significantly (25% or more) underinflated tire. These underinflated tires cause the USA to waste 2.8B gallons of gas/year (1.6B cars & light trucks, 1.2B heavy duty trucks). Over $11B in wasted money in the US alone due to underinflation.
By maintaining proper inflation pressure longer, nitrogen inflated tires get better gas mileage and have a longer tread life. Goodyear recognizes that underinflation is a major contributor to poor gas mileage and tire life, and are running a summertime air inflation program to combat these issues. More information is available here:
http://tirenitrogen.typepad.com/tirenitrogen/2008/05/goodyear-summer.html
While I doubt that this is proof enough for you that nitrogen tire inflation makes sense for the common consumer, I would hope you could at least understand the proposed benefits a bit better.
I will begin by stating that I have twenty years experience in the tire and automotive industry and cannot understand how people can fall for this bill of goods. The argument for nitrogen inflation is an industry driven phenomenon. The reason the people run around on under-inflated tires is a lack of maintenance. And anybody that has a tire that is more than 25% under-inflated is because they refuse to have the slow leak fixed. Having nitrogen in your tire will not plug the hole. I live in northern Canada where the temperatures vary widely and the pressure in my tires rarely are off by a pound or two even in the cold. Again we are being told that if we just do this or buy that we can avoid the responsibility of looking after whatever it may be. TPMS systems in new vehicles are a perfect example of this. They are supposed to prevent people from driving when a tire goes low yet in owners manuals the first thing car manufacturers tell you is the TPMS is not a substitute for proper tire maintenance. Once again the snake-oil salesmen are back with a new improved method to take your money. If you believe in nitrogen inflation I have some PVI (platinum vapour injection) systems for sale. For the average consumer nitrogen is a waste of money for the supposed gains.
[...] but since it ended up being so lengthy, I decided to make a separate post. The original comment is here and was caught by the Akismet as spam. I’ve since approved it to be [...]
I’ve responded to the comment above as a separate post found at: http://ahotcupofjoe.wordpress.com/2008/07/16/nitrogen-tire-scam-part-3/
Utter SCAM!
Claims about expansive behavior of water vapour are all based on 14 year old school kid physics. A tyre filled from 1bar atmosphere with wet 100RH air at 15°C holds 10.7g water / Kg air. 195/60R15 tyre that’s about 1.4g of water. At 32psi the boiling the point of water isn’t 100°C, it’s 136°C so no boiling and no expansive steam in a 80°C tyre or even 100°C F1 tyre. The actual increase in pressure at 80°C due to vapour pressure of water is about 0.7psi.
All compressors at tyre shops and service stations should have a dryer fitted. Just compressing air to 100psi reduces the amount of water air can hold at 15°C to 1.34g water / Kg air. Let it stand and the excess condenses in the tank to be released though the drain tap. Tyre filled to 32psi with air at 15°C and 1.34g water / Kg air will show a 0.03psi overpressure at 80°C. If you don’t let it stand and cool you will have under pressure problems as the air pressure reduces as it cools to ambient in the tyre. Get a tyre fitted at a busy shop with a hot compressor and you will always have low pressure the next day.
http://www.getnitrogen.org/pdf/graham.pdf
Statement: Diffusion rate for N2 is 3, O2 it’s 10. (3rd para from end)
Air contains 78% N2, assume rest is O2
Total diffusion rate of air = N2 0.78 x 3 + O2 0.22 x 10
= N2 2.34 + O2 2.2 = 4.54.
The N2 is exiting the tyre 6% faster than the O2!
93% N2 diffusion rate = N2 0.93 x 3 + O2 0.07 x 10
N2 2.79 + O2 0.7 = 3.49.
Ratio = 4.54/3.49 ~ 1.3
Assuming all loss is diffusion. A tyre with N2 will have same pressure after 6 months as an air filled tyre has after 4.6 months. All it can possibly do is allow you increase the pressure check intervals by 1.3. Every 9 days instead of every week.
Yet the N2 industry makes claims that it’s 3x better (or in the case of Bridgestone 6x). Seems yet again they can’t do a proper analysis but have relied on school kids.
People that fill with N2 are even less likely to check the pressures as they don’t have the N2 to fill them with (though bridgestone do say top up with air). After all it’s sold on the claim that tyres become virtually maintenance free (I can see some law suits real soon). If it takes a special trip to somewhere with a N2 machine then it’s an environmental disaster due to the fuel used making that trip.
Then there is issue of what the temperature is when you check the tyres pressure. Start with 32psi, the temperature you set the pressure at gives several psi variation in running pressure as does the running temp.
temp °C at 60°C at 80°
0 42.26 45.7
5 41.23 44.6
10 40.25 43.5
15 39.29 42.5
20 38.37 41.5
Doesn’t matter if it’s dry air or dry N2 both obey the Ideal gas law. P x V / T = const.
Then there is there is the “they use it on aircraft” crap. They use O2 reduced air, requirement is 5% or less O2. A plane took off with a brake on. This overheated the brake and tyre a lot. It didn’t blow out straight off but it was slowly cooked by the overheated brake. CAP 747, appendix 1, GR No. 16 Tyre Bursts In Flight – Inflation Media. 2.5Mb pdf doc source on this page, link “open doc in new window”.
http://www.caa.co.uk/application.aspx?categoryid=33&pagetype=65&applicationid=11&mode=detail&id=1331
Only applies to aircraft with RETRACTABLE undercarriage and over 5700Kg. I’ve yet to see a car or truck driven on retractable wheels.
Peter,
Sorry it took more than 10 days for me to approve your comment. I’ve been more or less away recently and Akismet caught it as spam since it had several links in it.
Anyway, great stuff! Thank you!
Carl
I also wrote a post ( http://energy-eng.blogspot.com/2008/03/nitrogen-filled-tires-myths-and-reality.html )
on why the nitrogen molecule is larger than oxygen molecule, even though N (atomic # 7) is less heavier than oxygen (atomic # 8).
The difference lies in “kinetic diameters”. More is here
http://www.getnitrogen.org/pdf/graham.pdf
Ultimately, my back-of-the-envelope calculations indicate that a N2 filled tire will hold its pressure for ~40% more time , compared to the air inflated tire.
The real question is whether we are actually checking our tire pressures, rather than what we are filling it with.
Nitrogen doesn’t expand under heat like regular air does (or very minimally, relatively). It’s this singular property that makes it optimal for race cars / motorcycles that need predictable tire pressure. It’s unnecessary for everything else. Just check your tire pressure when you get your oil changed like you should.
You get the same MPG benefits by filling your tires to their max pressure with any air gas.
PS: The only thing you can accuse the salesperson of is selling refrigerators to eskimos.
I do not know the entire chemistry bit, however I do know that its a way we can become more lazy and not have to check our tires as frequently as we should. N2 has benefits, but when your oil hasn’t been changed for 5-8K miles or your putting E85 octane in your car to save money it won’t matter what goes in your tires if your car is not running @ 100% its capabilities. You can’t “Rob Peter to Pay Paul” ! You have to take care of your entire car and then you’ll know what mpg $$ you are saving, otherwise its just another expense putting N2 in your tires ! Good Luck !
Here is a scientific paper that does a good job of explaining why O2 permeates most rubbers more easily than N2. Basically, while O2 and N2 have roughly the same diffusion values in rubber, O2 is much more soluble in rubber. It is the combination of solubility and diffusivity that determines total permeability.
http://www.arlon-std.com/Library/Guides/D116%20Haibing%20Zhang%20et%20al.pdf
However, for many of the same reasons already stated in the original post, I agree that for the most part nitrogen-filling has a very, very limited benefits.
Nitrogen expands under heat, just like every other gaseous molecule. PV=NRT for oxygen as well as nitrogen. (If you forget your high school physics, this means that temperature and volume are directly related, for any “ideal” gas. Oxygen and nitrogen both reasonably approximate ideal gases for this purpose.
All I know is I bought my 2008 Toyota Camry with 5K miles on it. No one told me I had Nitrogen in my tires! After 4K miles I put on, I was on a trip and my “light” lit on the dashboard saying my tire pressure was low. I went for an oil change and asked the guy to fill my tires. He told me he couldnt due to the Nitrogen. I now have to go to the Toyota dealer on my vacation to have this checked out. I am not a fan of Nitrogen!! He said it was good that I didnt try to put air in the tire myself. So after 9K miles, I’m having problems!!
[...] Nitro in Tires – Today, 03:49 PM found a good link: Nitrogen Filled Tires: a Scam? Hot Cup of Joe …dead on with what I would agree to. [...]
[...] Originally Posted by nymyth Whats the purpose of this?? Im curious Peace Supposedly, Nitrogen doesn’t seep out of your tires are quickly since the molecules are larger than compressed air mixture. However, Compressed Air is already 80% Nitrogen. just googled and found this link: Nitrogen Filled Tires: a Scam? Hot Cup of Joe [...]
[...] (except those by the folks selling N2) saying it does a darned thing for street-driven vehicles. Nitrogen Filled Tires: a Scam? Hot Cup of Joe __________________ ‘97 F250 XL, 5.8L, ‘05 Escape Hybrid, ‘06 Escape Hybrid [...]
Maryann,
I don’t understand why you can’t add regular air to your nitrogen filled tires? You would just be reducing the percent nitrogen. I could see how it might be a problem if you later decided to refill the tires with pure nitrogen, but it seems you’re not too fond of the NitroFill anyways.
Ok first off, I run my families Tire Store. We have just acquired a Nitrogen inflation machine. While trying to “bone up” on the positives of Nitrogen, I found this website. Interesting to say the least!
As I read the posts I feel there isn’t a right or wrong answer to the question of putting Nitrogen in tires. There were some amazingly cool demonstrations of chemical breakdowns and more arguments of plan nonsense.
Another stated that since we have a majority of non-metal wheels now, there would be no rust. This is not true. Being our shop is near the beach in Southern California, we have continual problems with chrome peeling and wheels flat out rusting causing leaks to occur. Whether Nitrogen wlll solve this problem remains to be seen. But, if there is a chance that spending $5.00 per tire could spare a $300.00 tire from going flat, due to rust between the wheel and tire, then the math speaks for itself!
Another person claimed they could not put regular air mixed with Nitrogen. Unless I didn’t understand the earlier chem lesson, by mixing the two only the purity of the Nitrogen is compromised. So when I read of a shop saying they can’t work on tires that have Nitrogen, I’m baffled!
Lastly, we get requests upon requests for Nitrogen. By understanding as many benefits of Nitrogen as we can, we can give the proper prospective to the customer. Will we push it as a major way to save money and gas mileage, no.
Is it a scam….No…It is simply an alternative!
Steve, I completely agree. And, good wishes to you and yours in business and health! JDW
[...] article I found if you guys are interested in reading: Nitrogen Filled Tires: a Scam? Hot Cup of Joe Now I’m not saying filling your tires with Nitrogen is a scam, but this article makes some good [...]
I would like you to know we have nitrogen in our tires and it is a big problem. Because the caps are stainless steel and the stems are a different alloy,
They have corrodite. We are trying to get the dealer to
take care of the problem, which they have been awear
of. In order to fill the tire which got low the stem had to to be cut off and replaced to a tune of $85 dollars and we have three other tires which need to be addressed.
Forget the nitrogen tires, they have a problem.
“…our caps are stainless steel…”
So, how is it there’s an incompatability with stainless?
Valva stems are made of steel, or brass. I’ve never before heard of corrosion between the two. Are you being told NITROGEN is the real culprit? Air is comprised of 78% N2, so, how’s that possible?
[...] article I found via Google, read it and others you’ll find and either laugh or fall for the hype.. Nitrogen Filled Tires: a Scam? Hot Cup of Joe __________________ "Fill your hands you son of a bitch" Rooster [...]
Geez, I get 70,000 miles from my air-filled tires with no visible deteriorization. Eventually, the treads wear and I need new tires. So, what will nitrogen do for the most destrutive issues with my air-filled tires-TREADWEAR? I just hate people who scam the public like these guys are trying to do. They must work for the Bush administration!… did the Moon rover have N fills?
Yes, it did.
I was at a tire shop today and saw this scam as well. I just started laughing at the diagrams. Here’s what Nitrogen looks like in a tire, versus here’s what Oxygen looks like. I don’t know a single person that inflates their tires with Oxygen…um…we use regular old mixed up air.
I haven’t had chemistry in 20 years, so I was thinking air was 74% Nitrogen (maybe that’s the percent of the earth that’s water?) but regardless, I have NEVER had tires lose air pressure for anything other than having a nail in them (once in my life) or just seasonal temperature changes…fill up in the fall. Air is free at gas stations and has never been the cause of my tires’ need of replacement.
Maybe if you let your car sit around in a showroom for years the air would do damage to the rubber before the treads wore out, but if you actually drive your car, I doubt that will ever be a problem.
Good assessment and I wholeheartedly agree. Airplanes and the Space Shuttle use Nitrogen in their tires because it expands less with thermal variation than air does.
I bought new tires at Costco, including the nitrogen thing. Nothing I read here tells me it’s a flaming wonderful idea, altho it might provide modest benefits.
The mechanic who services my car says he can’t check the tire pressures, let alone add air to the tires. So the pressure doesn’t get checked as often as if I had air!
I just called Costco and was told that their “free” service would likely take 1.5 hrs. just to get to the front of the line, and another who-knows-what to rotate the tires and check pressure. I don’t have that kind of time and I certainly don’t want to hang out at Costco in my “spare” time.
I am getting elderly – I still have a compressor and a pressure gage, but due to ill health I haven’t worked on cars for a couple of years. I used to restore old cars.
So… my question. What is the danger in adding air to nitrogen-filled tires to restore pressure? Can it be done (like, are the valve-stems incompatible with my gauge and compressor chuck). Because of my health it’s a lot easier to write this question on the computer than it is to actually check this myself – sorry I sound lazy.
Thanks
Richard
Hi Richard,
filling up with regular air will only reduce the “purity” of nitorgen in your tires. i.e from 95% to worst case 78% Nitrogen. There is no danger to it and can be done with your regular equipment that you use to fill tires.
Richard, you’re gonna be OK. There is NO danger to adding ‘regular ol’ air’ to your “special” tires. No differences in stems, etc. You’re gonna be just fine.
However, you will lose a couple hundreths seconds off of your Laguna Seca lap times! Sorry dude!
OK so if oxygen diffuses thru the tire wall faster than Nitrogen, then assuming I fill with air initially and don’t have a flat tire, and just keep the pressure where it should be with air, (78% N2) , the tire will slowly become filled with pure nitrogen. If this takes a long time to happen, then all we are saying is that the oxygen doesn’t leak out very quickly. I fail to see any reason to put pure nitrogen in my tires, let alone pay for it.
I’m fairly sure that a lot of water vapor in tires is undesirable so there should be some benefit to using nitrogen or dry air to keep the water vapor low. As for the nitrogen itself, I think the gas in tires should naturally increase in nitrogen level over the life of the tire. Assuming the statements about nitrogen and oxygen diffusion are true, the oxygen part of the gas should leak out first leaving a higher than 78% portion of nitrogen. Every time the tire is brought up to pressure with air, the percentage of oxygen will be less than the previous filling. Eventually the tire should have a very high percentage of nitrogen. I think I have actually seen this happen as new tires seem to lose pressure more rapidly until they have been refilled several times.
I don’t know if anybody has already stated this.. because I didn’t want to read through every single comment, but I would like to say, there should be almost no difference at all..
This is because air, which is what we put into tires regularly is around 78% nitrogen.
Meaning putting nitrogen in your tires would only be increasing the percentage by what, 20%? It will not make a difference, and it is a scam. Some new way to make money, or else it would have been out years ago, and not just now as a fad.
We have been in the tire business for 50 years and anybody thats dumb enough to pay to have nitrogen put in their tires deserves to lose the money they paid. I just want all their names so I can sell them air in a jug to breath. When your racing for millions you may want to try nitrogen for daily driving your just a fool!
[...] but since it ended up being so lengthy, I decided to make a separate post. The original comment is here and was caught by the Akismet as spam. I’ve since approved it to be [...]
Here is the third letter I’ve written Modern Tire Dealer magazine about this issue. Some of the editors supposedly wanted to publish the first one I wrote, but were over-ruled by the publisher. Too many advertiser make nitrogen generators. Two editors, one a managing editor, and the editor called me and I had lengthy conversations with both. In the end, the advertising big bucks won the day.
This was in response to their August ‘09 issue in which they “re-visited” the nitrogen issue to see if their past claims “needed adjustment”. Needless to say, it was just a re-write of earlier articles praising the “benefits” of nitrogen. It was entitled “Analyzing the Benefits of Nitrogen Inflation”. Not the issue, but the “benefits”.
They no longer respond to my emails.
Here is my letter (text taken from MTD are in quotation marks):
MTD: “CLAIM: Tires hold their psi longer with nitrogen than air. This is true…”
But is the difference enough to be significant? The University of Bologna puts the loss at 1.6 vs. 3 % per month. In a tire that was originally inflated to 32 psi, this is .512 vs. .96 psi. Less than ½ lb.. Most air gauges won’t even read this. Consumer Reports says the loss is much less, .18 lbs. vs. .29 lbs. per month, from a starting point of 30 psi, if memory serves. .11 pounds. That’s “point eleven”. Eleven one-hundredths of one pound. (Getnitrogen obviously was not pleased, and tried to discredit CR’s findings by saying the tires were on a “test stand” and would therefore lose less air than tires being used. To MTD’s credit, they dismissed this theory. It has been my experience that tires being used, or run, lose less air than those that are not).
The claim is that nitrogen molecules are “larger” than oxygen molecules. In fact, they are-a mere 3% larger. According to what I’ve found, nitrogen molecules are approximately 300 picometers compared to oxygen molecules, which are 292 picometers. Thus, proponents of nitrogen would have you believe that the “pores” in tires are somehow magically kept below 300 pm, which would prevent the escape of nitrogen, but larger than 292 pm, which would allow for the escape of oxygen.
But, most damning of all, if what Getnitrogen and the rest of the proponents of nitrogen tell us is true, once a tire has lost approximately 22% of it’s original pressure and this pressure has been restored, this tire then has approximately 95% nitrogen, which is more than the 93% advocated. This holds true whether the tire is a passenger tire with 32 psi or a truck tire with 100 psi.
Even if some of the nitrogen does leak out with the oxygen, (which sort of defeats the purpose, doesn’t it?) after a couple of these loss-refill cycles, you would still end up with, well, what others are paying big bucks for, for free.
MTD: They wrote that the performance results at 96% were not substantially different than at 99.9%.
“This is important for the average consumer because the need to purge existing tires completely of air before filling with nitrogen may not be necessary,” they concluded.
(“Effects of Nitrogen Inflation on Tire Aging and Performance,” authors John Baldwin, David Bauer and Kevin Ellwood )
Translation: The machines that are supposed to produce 93% nitrogen may well produce somewhat less, and the technicians that are in a hurry to get to the break room are not going to purge your tires the required number of times. After all, who’s going to check for purity? And you’re going to wind up with something above 78% IF you’re lucky.
If the results at 96% were not substantially different than at 99.9%., would they be substantially different at 92% than at 96%? 89% than at 92%? What about at 78%?
MTD: CLAIM: “Properties of nitrogen minimize deterioration of rubber and tire cords.” If the purity of nitrogen in the tire is high enough, yes. In the Ford study, the authors concluded that “the oxidation of the steel-belt rubber is truly driven from the contained air pressure inside a normal passenger or light truck tire.”
Tires do not deteriorate from the inside. Just last month we pulled one off that was 15 years old, according to the DOT number. The outside had the worst weather cracking I’d ever seen. You could literally put a nickel in the cracks. The inside looked like new-shiny, black, supple. I’ve never seen a tire that has been mounted and maintained with any visible deterioration inside. If “the oxidation of the steel-belt rubber driven from the contained air pressure”, why is the inner liner so unaffected?
MTD: CLAIM: “For customers who drive a lot, nitrogen makes a big difference in their pocketbooks,” said McCune, who uses ready-made tools like fuel savings calculators on various Web sites, including http://www.getnitrogen.org). We checked out three such calculators, one from a supplier, one from a dealer and one from http://www.getnitrogen.org. We put in these numbers:
What in the world does this prove? You used three calculators from three sources, all three of which have a vested interest in the promotion of nitrogen.
The average fuel savings by using nitrogen, all things being equal, is about 3.3%, according to the Get Nitrogen Institute, http://www.fueleconomy.gov and a Canadian study of trucking fleets conducted by a nitrogen tire inflation equipment supplier.
MTD: “…according to the Get Nitrogen Institute.” “…conducted by a nitrogen tire inflation equipment supplier.”
Once again, MTD has relied on obviously biased sources to reach their conclusions.