By on October 30, 2007

nitrot1.jpgJet planes, armored personnel carriers and racecars all have nitrogen-filled tires. So it’s got to be cool, right? I mean, I wish my Honda Odyssey minivan was more like an F-22 in some way. Or in any way. Anyway, is it worth an average five bucks a tire to stuff your rubber with the seventh element? For the majority of American drivers– those who do not routinely drive through flaming pools of fuel, off-road on dunes hotter than Scarlett Johansson’s hips or hit 200mph on the straight-aways– the answer is a simple “no.” Yet thousands of vendors are setting up nitrogen pumps and enticing people to pop open their stems. What’s the point?

Purified nitrogen is more stable and less corrosive than a compressed version of the air we breathe. By its lonesome, nitrogen clumps in large molecules. Even better, it's not oxygen, which is the root of oxidation, which eats rubber just like steel, just not as dramatically or visibly. All of this means the gas has two things going for it.

First, compressed air is a blend of oxygen and other tire degrading contaminants, including water. Your tires should last longer filled with pure, dry, nitrogen gas. Second, nitrogen’s larger molecules are less likely to seep through rubber. Nitrogen-filled tires delivers more consistent inflation pressure– especially under temperature fluctuations. Studies suggest nitrogen-filled tires will remain properly inflated three times longer than air-puffed companions.

Nitrogen's advantages are solid (so to speak)– provided you're a diligent motorist and nitrogen refills are free. Add some nonchalance and a dollar figure and the benefits evaporate.

Oxygen only accounts for about 21 percent of the ambient air (nitrogen makes up 78 percent). And oxygen is going to eat the outside of the tire– no matter would put inside. And if you don’t drive that much, you’re not getting the air inside all hot and bothered, which increases the decay rate.

In truth, most drivers are going to wear out their tires long before the rubber will decay enough to lower tire performance or safety; those radials will last until much of the gas– any gas– seeps out. I repeat: whether you drive a lot or a little, internal tire degradation isn’t much of a worry.

Proper inflation is the real issue. Under-inflated tires reduce gas mileage. They flatten out, creating more surface area and thus adding friction, which makes the engine work harder. The extra friction, and resulting heat, also increases the chance of a blowout. A properly inflated tire is always safer and more efficient than under-inflated shoes (unless you're driving across a sand dune). 

Nitrogen’s reluctance to leave the wheel is a blessing because it helps maintain tire pressure at optimal levels. Of course, checking your tire pressure once a month does the same thing. AND regular checks get you close to the rubber for a chance of seeing something else that might be going wrong: weird wear, a protruding rail spike, a chunk scraped away by that curb you forgot you hit, etc.

In any case, tire manufactures reckon your tires lose around one pound per month of inflation pressure. There are a ton of variables, but the National Highway Traffic Safety Administration says that maintaining recommended pressure improves the average driver's gas mileage by three percent. That’s about $50 a year just for paying attention– not to mention the better handling and reliability that come along for the ride.

Yes but– nitrogen is still going to leave the inside of your tires for the big, wide world; just not as quickly as oxygen. A pound's worth of gas might seep out in three months, rather than one. Meanwhile, the idea that nitrogen-stuffed tires are a fill-it-and-leave-it alternative to air is an inherently dangerous supposition. Drivers still need to get down, stick on a gauge and hear the hiss whether they’ve used air, nitrogen or cream filling. Nitrogen hype can end up doing more harm than good.

Goodyear Tire & Rubber Co. is ambivalent about the use of nitrogen. The Rubber Manufacturers Association says it it's a good thing– when it's free. Michelin goes a step further. They recommend nitrogen only for tires used "in high risk environments” like aircraft landing gear and racing.

A quick look at a few of the nitrogen generator manufacturers' websites can give you an idea what may be driving some of the interest in swapping tire gasses. N2 machines can operate for as little as 25 cents an application. The generators themselves go for as little as four grand. After the first 200 or so nitrogen fill-ups, these things are more profitable than pretzel carts.

As with most things, it’s all about me. I’ve got to be more conscientious about checking and rotating my tires. If I want them to be all they can be, I’ve got to be better. It’s what’s inside that counts-– or, in the case of nitrogen, not. So, to make my minivan more like a fighter plane, I’m looking at other modifications. Possibly chaff.

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69 Comments on “The Truth About Filling Your Tires with Nitrogen...”


  • avatar
    Virtual Insanity

    So, why is it a bad idea to use Nitrogen?

  • avatar
    jaje

    Funny thing was Ford had a directive to dealers to deflate/inflate tires to 26psi on the Firestone equipped Explorers and trucks in order to increase stability (this was the minimum level recommended – but internal memos at Firestone wanted 35psi). This lead to more wear and tear on the tires as they lost air and inattentive drivers never checked them while playing slalom in traffic. We all know how that all turned out.

  • avatar
    johnf514

    Great write-up, Mike. It’s good to see how while this product has it’s “benefits”, I can get 78% nitrogen air for free! :)

    “So, to make my minivan more like a fighter plane, I’m looking at other modifications. Possibly chaff.”

    Might help with police radar. ;)

  • avatar
    Slow_Joe_Crow

    @ Virtual Insanity
    Inflating tires with nitrogen is fine, believing marketing hype that nitrogen is a panacea for tire problems is bad. The theme of this article is that nitrogen tire inflation is the equivalent of those fluid flush machines at the quick lube place, primary benefit is to the bottom line of the dealer.

  • avatar
    Stephan Wilkinson

    He’s not saying it’s “bad” idea, just that it’s a dumb one, at $20 per tire-set.

  • avatar
    starlightmica

    If you get your tires mounted at our local Costco, they will refill your tires with nitrogen for the life of the tires. So as long as you’re not paying, it’s fine.

  • avatar
    miked

    In fact “Dry Air” would be just as good as Nitrogen, but it costs about the same to make, so most people just stick with N2. The main reason Race cars, airplanes, and other “high-risk environments” use N2, is just because it doesn’t contain water. Without the water the pressure stays more constant over the operating temperature. That’s important for an airplane. Take off in Florida at 80 degrees and land in New York at 30 degrees? You want the tires to be at about the same pressure. If the water in the tires condenses (or freezes) then it takes up much less volume and the tire pressure will drop dramatically.

    For passenger cars, the tire temperature is remarkably constant (compared to airplanes and race cars), so there is no need for N2 filled tires. Of course there’s no harm, so if your neighborhood gas station offers free nitrogen, go ahead and use it, it just won’t do anything for you.

  • avatar
    Virtual Insanity

    Ah I see. Just ignore me then, I’m the reason marketing exists.

  • avatar
    carlisimo

    My tires only last a year anyway. Not enough time to degrade or go through that many monthly pressure checks.

  • avatar
    Stephan Wilkinson

    I hear you, Virtual Insanity. Just bought a $140 infrared pyrometer (tire-temp, etc. sensor) instead of the $90 model. Why? Well, uh, it must be $50 better, right? Besides, someday I might have to sense the temp of molten iron, right?

  • avatar
    William C Montgomery

    Virtual Insanity: So, why is it a bad idea to use Nitrogen?

    It’s a very bad idea if you ever think you might drive your car into a lake or river and plan to breathe the air in your tires ala James Bond. But I digress…

  • avatar
    GS650G

    Bicycle tires are inflated with nitrogen for serious competition, like the Olympoc track events. Apparently it maintains the high pressure better ( up to 230PSI ) and does not change pressure due to temperature changes. I have ridden on tires inflated to 230psi and the deflection is non-existent. But the tire must be worked up to the pressure gradually with regular air, the tire is inflated to 170, allowed to cool, and then taken to 230 in stages.

    What kind of tire is rated for this level? Continental GP 3/4″ tubular. maximum burst pressure is around 600 for this handmade tire.

  • avatar
    red60r

    Interesting — Costco (at least where I am) routinely fills new tires with N2 and will refill for free as long as you bought the tires from them.

  • avatar
    KBW

    It’s a very bad idea if you ever think you might drive your car into a lake or river and plan to breathe the air in your tires ala James Bond. But I digress…

    Fear not, that particular stunt doesn’t actually work.

  • avatar
    SherbornSean

    KBW,
    Why doesn’t it work? I had been counting on it for the next time I have to escape from Grace Jones.

  • avatar
    luiz.stockler

    Do I have to worry about raccooons eating my seat?

  • avatar
    Martin Albright

    I rub my tires with snake oil every weekend to keep them supple.

    I have hear that things like Nitrogen air and slick 50 are very good for removing excess deposits of cash from your wallet, though.

  • avatar
    ash78

    What about if your car is born from jets?

    Sorry, couldn’t resist. Nice writeup. I’ll continue to stick with my 12v air compressor, bought for $9 at Wally World 4 years ago, which fits nicely into a cubby hole in my trunk.

    This might be a tangential “pro” argument, but the discipline in checking your tires every 2-4 weeks (along with oil, tire wear, etc) is a good policy in keeping your car in good shape. Anything that urges people to stay AWAY from their cars, IMO, is a step in the wrong direction, even if it is tecnically sound. We need people MORE aware of their vehicles, not less.

  • avatar
    SunnyvaleCA

    This does show that some consumers are willing to go through the effort to use nitrogen to get a small fraction of a single MPG fuel efficiency improvement. Oh… never mind: they are really willing to get the N2 because they think they won’t have to worry about tire pressure again.

    New Jersey and Oregon mostly require gas station attendants to pump the gas. Could those states require that the attendants also check tire pressure? That might be effective. With modern credit-card machines, the attendants don’t seem to be too busy anyway.

  • avatar
    nonce

    I’ll tell ya, checking my tires pressure is a real hassle. If I could put something in it that would let me go three times as long without worrying about my tires, I could see paying for that convenience.

  • avatar
    altoids

    Great article! TTAC at it’s best.

  • avatar
    Virtual Insanity

    Stephan, this is an almost exact conversation I had. Shows you how well marketing works.

    ME: I think I’ll just get the HKS SSQV replacement for my car.
    FRIEND: Why? Forge makes a valve that is an exact facotry replacement, but made out of metal instead of plastic. It costs less, looks good, and is easier to install in bypass mode.
    ME: Well, the SSQV is good enough for 1000+ WHP Supras and Skylines, so it must be just fine for my car.

  • avatar
    shortthrowsixspeed

    in truth, i’ve never considered putting nitrogen in my tires. i check them regularly, and they’ll wear out from hard cornering long before oxidation has time to do anything. but . . . i do think it would be cool to tell people that i just had my tires filled with Nitrogen. isn’t that the draw? there are so many things that people buy that aren’t good for anything other than a few pats on the back of their self image. in this resepect, costco’s got it right: get your tires and your ego inflated here.

    excellent write up by the way.

  • avatar
    ash78

    All of this just seems like part of the broader attempt to keep shops competitive as cars become more and more reliable. I mean, cars rarely leave people stranded like they did just 20 years ago. But I don’t see any fewer repair shops. I see more. And I see more and more offers for pseudo-procedures, like Nitrogen tire fills and $200 fuel system cleanings.

    Sales. PT Barnum, etc.

  • avatar
    zerofoo

    miked, Check out the ideal gas law:

    http://en.wikipedia.org/wiki/Ideal_gas_law

    And Boyle’s Law:

    http://en.wikipedia.org/wiki/Boyle%27s_law

    Neither air or pure Nitrogen will give you the pressure stability you describe with those temperature variations. Aircraft tires are designed to operate at high pressure so minor pressure fluctuations don’t hurt the performance of the tire. (Don’t forget altitude changes also cause the internal tire pressure to fluctuate).

    You are right about the water vapor problem. The answer there is to use compressed air from the same source that drives the shop’s tools. Those compressors have dryers installed on the air lines to prevent moisture from getting into the air tools and causing corrosion.

    -ted

  • avatar
    Lumbergh21

    TANSTAAFL. Anybody whose taken an economics class and plenty who haven’t, I’m sure, know what this means. “Free” nitrogen isn’t really free. Do you think they are taking money out of their profits for the equipment to provide the “free” nitrogen? Actually, I’m sure they’re adding to their profit. Charge a couple of bucks extra for each tire but add this “free” service that probably costs them less than a dollar per tire sold. They increase both their sales and the profit per tire sold. Better yet, others are working and paying for bogus advertising telling you how nitrogen in your tires will make you just like a NASCAR driver. Does it get any better.

    Could somebody explain how the pressure varies significantly less with respect to temperature when dry nitrogen is used versus compressed air. I understand that water in the air can condense in your tire reducing the pressure until the tire warms up enough to vaporize the water. But, is there really that much vapor in water that the vaporization and condensation of water makes a significant difference versus the increase in pressure simply by virtue of the increase in temperature? I can’t imagine why there would be any significant difference in the behavior of dry air and dry nitrogen. It is possible that pure nitrogen will behave more like an ideal gas than air(I don’t have that info at my fingertips anymore), but would the variance from an ideal gas be significantly less for nitrogen than air, particualrly as it applies to everyday or even long haul driving? I doubt it. So, somebody like me with an air compressor with a drier (dry air) for use with pnuematic tools would reap no benefit from using compressed, dry nitrogen it seems to me, and isn’t this the case with most tire shops? Don’t they use the same air (dry air) to inflate tires as they use for the pnuematic wrenches?

    I was under the impression that Stock Cars and Dragsters used notrogen for a reason not mentioned. Flammability. They perfer not to keep large tanks of compressed oxidant (the oxygen in air) near the fuel.

  • avatar
    Lumbergh21

    Geeze Zerofoo, you beat me to the punch answering the questions I posed before I even finished typing them.

  • avatar
    SpacemanSpiff

    A local Police Department recently switched to a Nitrogen fill in their patrol cars. This prompted a story on the local news with video of the Nitrogen machine filling the tires, in-car video and even an interview with an officer. He swore that the ride on Nitrogen filled tires was much smoother and that the cars would get more miles per gallon!
    Once I picked myself off the floor and stopped laughing, I called my buddy who works for that department and told him he needed to quit, because he was surrounded by idiots.

  • avatar
    Queensmet

    Within the next 5 year it would not surprise me if every car has pressure sensors in the tires. This is even more expensive than N2, but you get a digital readout on your dash. If it were a “heads-up” your car really would be like a jet fighter.

  • avatar
    rpn453

    Good article.

    I’ve never seen evidence of my tires, or anyone else’s, degrading from the inside, so I’ve never even considered using nitrogen.

  • avatar
    philbailey

    The air we breathe is 78% nitrogen and the other 22%
    is oxygen, so your tires already have a lot of nitrogen in them. Garages that have invested as much as $5000 in a nitrogen generator, which extracts the gas from the air and dries it, will tell you that racing cars use it, aeroplanes use it, that your tire pressures will remain much more stable and that the pure nitrogen doesn’t support oxidation so the tire doesn’t rot from the inside.

    Oh and by the way, there’s a $10 charge for filling each tire.

    On the other hand, there appears to be absolutely no harm in using nitrogen to fill tires, so as long as the shop doesn’t
    hit you with any extra charges.

    There are statements made like “Nitrogen doesn’t support combustion, so its safer”.

    We’ve always seen tire treads wear out before the casing gives up, so I don’t believe that oxidation of tires is that
    big a deal. I believe we’re into another snake oil situation, but one that’s a bit more scientific and therefore more difficult
    to nail down.

    Here’s why:

    Dry air or dry nitrogen will follow the combined gas laws more accurately than air containing moisture, but the difference really is academic.

    Oxidation of the rubber inside a tyre has never been of concern to me, nor anyone else I know.

    I have only ever seen tyres fail from normal wear, cuts from impact or sharp objects or by oxidation or ozone attack of the
    outer carcass. The cracks in the sidewall, always start outside, never on the inside.

    Race car teams will often use nitrogen to fill tires, but largely out of convenience rather than due to any performance benefit.

    No ancillary equipment is needed to fill a tire if you have a bottle of nitrogen on hand.

    If you use a compressor, you either need a generator or need to find a place to plug in, or need a gas powered compressor.

    In racing applications the best option is nitrogen, next is really dry compressed air, last is wet air from a compressor.

    100% nitrogen will carry less moisture than what’s in the atmosphere. Condensation inside the pressure tank of a compressor can be corrosive and may have unpredictable thermal properties. Formula1 teams now make tire pressure adjustments in 1/4 psi increments to correct handling so the thermal effects are significant. I don’t think there will be any benefit on a Cadillac Escalade.

    When a tire heats up, the air and any moisture inside it heats up as well. When the moisture inside the tire heats up, the water molecules move further apart, increasing the tire pressure. By removing this moisture, the pressure stays more consistent over the entire heat cycle of the tire.

    On a race car, a 1/4 psi difference can change the handling of a car significantly. The humidity inside a tire does not have to
    be zero, but if it is not at least kept consistent from one set of tires to another, to equal a 1/4 psi increase in the current set, a 1 psi change may need to be made in another set because of the differing humidities.

    Is nitrogen completely necessary? No. Air can be dried using inline air dryers and such. However, it’s much easier to keep
    tire humidity consistent when all the tires can be filled from the same 1500 psi bottle of nitrogen delivered to the shop.

    As far as race tires go, this is the reason to use nitrogen. Because of the short life of a race tire, how much air permeates out of a tire over a year is of no concern.

    Commercial aircraft tires are routinely nitrogen filled.

    Apparently, one of the reasons behind using nitrogen in aircraft tyres is that they fly up to 40,000 ft where the temperature can be as low as -60C.

    Any water in the tyres will freeze and is not likely to thaw completely before landing.

    If it settles in one spot, then the tyre has to break it free when it flexes and there is the possibility of causing an unbalance as the tyre spins up from zero to 130 mph. I can see the cold and condensation freezing in the tire as a concern in aircraft.

    Aircraft tires are pressurized to something like 250 – 300 psi. It is far easier to do that with a nitrogen bottle at 1,500
    psi than maintaining a multi-stage air compressor and high pressure drier.

    The logic behind the statement that because the nitrogen molecule is larger and therefore is less likely to permeate
    through the tire than oxygen needs to be verified. In fact, air leaking past valve seats and bead to rim joints is a
    much greater problem in car tires.

    Fighter jet brake fires used to be common place, even after the fire had been covered with powder the pads would
    smoulder for some time. If the tyre failed it was better that Nitrogen be released over the smouldering pads than air.

    A large amount of heat is generated by the brakes when stopping a fast jet, the aircraft then trundles at a walking pace back to the gate so very little cooling air is available to dissipate the heat. The aircraft is then left to stand and the heat soaks into the tyres. Allegedly Nitrogen is better able to withstand this heat soak than air.

    Some large trucking fleets use nitrogen too. It increases the life span of the tire carcass which can be pretty long since
    they retread them forever. This is not a factor on passenger cars.

    I have seen tyres that need a regular top up, but I have also seen tyres that hold pressure for a year or more.
    Surely with a matched set of tyres, the difference in ability to hold pressure is due to leaks, not difference in diffusion rates.
    The loss due to diffusion is in my opinion, negligible, and I would expect in the order of less than 1% per year.

    For a street car, I can see little benefit in using nitrogen. But then again, if you check your pressures just about every week, and don’t worry if pressures increase 1 or 3 psi during a daily commute.

    As far as corrosion resistance is concerned, rusting will only occur when the oxygen in the air can reach bare metal.
    Unless for some reason your steel wheels didn’t come painted or the surface was damaged before the tire was put on, the side of the wheel open to the ambient air will corrode much, much faster. Alloy wheels, of course, will not corrode from moisture or oxygen exposure

    The bottom line becomes one of special applications and so what’s sauce for the goose (race cars and aeroplanes) is certainly not sauce for the gander (car and SUV owners).

    If you can get it for free – take it. If there’s a charge, refuse the offer.

  • avatar
    blautens

    Queensmet –

    I believe tire pressure monitoring systems were required on all passenger vehicles produced for sale in the US after September of this year.

    You can sift through it here:
    http://www.nhtsa.dot.gov/cars/rules/rulings/TPMSnprmPost2Cir/TPMSnprmPost2Cir.html#II_B

  • avatar
    lantius

    If the point is that you should fill your tires with nitrogen because nitrogen leaks out more slowly, then you’re already fine. You’re filling your tires with 78% pure nitrogen, and it’s leaking out more slowly than the oxygen. When you top your tires off, you’re actually increasing the nitrogen purity in your tires. After many iterations of filling it and letting the oxygen leak out, you’ll end up with mostly pure nitrogen in your tires anyway. Science!

  • avatar
    Landcrusher

    I want to know where people are getting their tires filled up for free? Unless you pay for full serve around here, you have to drop quarters into a machine. The machines work only about half the time, and half of the failures are followed up with a story about having to write the vending company to get your money back.

  • avatar
    Lumbergh21

    Landcrusher :
    October 30th, 2007 at 5:12 pm

    I want to know where people are getting their tires filled up for free? Unless you pay for full serve around here, you have to drop quarters into a machine. The machines work only about half the time, and half of the failures are followed up with a story about having to write the vending company to get your money back.

    In California, where I live, I believe that teh gas stations are required to provide air and water to their customers for free. In the past I could usually wait until the next time I needed to fill up teh gas tank before using the free air that came with it. Now, of course, I just use the compressor in my garage if I feel the need before my next fill-up.

  • avatar
    ghillie

    Proper inflation is the real issue. Under-inflated tires reduce gas mileage. They flatten out, creating more surface area and thus adding friction, which makes the engine work harder. The extra friction, and resulting heat, also increases the chance of a blowout. A properly inflated tire is always safer and more efficient than under-inflated shoes (unless you’re driving across a sand dune).

    I thought that the increased fuel consumption from underinflated tires comes from the energy used to (constantly) deflect the side wall as the wheels rotate. Higher pressure gives less side wall deflection and less energy used. I thought that the increased friction from more surface area of the tire in contact with the road was not significant.

    Does anyone know which is correct?

  • avatar
    rpn453

    Landcrusher, I use the compressor in my garage. :)

    I think this is all about the North American ideal to have “the best” regardless of cost. Nitrogen is the best thing to fill your tires with, so a good consumer should demand it! The fact that it makes no difference in their application is not important. Look how many people use synthetic oil for standard drain intervals in a vehicle that doesn’t require it, even though they pass the same tests and meet the same specifications as regular oils, and haven’t been shown by UOAs to make any difference in normal driving situations. Sure, the base oil of a synthetic is of better quality but, as with nitrogen in the tires, it doesn’t actually matter. It just feels good to know that you’re buying and using the best you can, in case you might need it. But I’m weird, so for me it feels good to do things in the most efficient and economical way possible.

  • avatar
    rpn453

    ghillie, I believe it is mainly due to deformation of the tread mass and sidewalls. I’ve been told by a tire engineer that a tire’s fuel economy is primarily dependent on the mass of the tread. This makes sense to me since it is the mass that is continuously being deflected while driving, and less tire pressure equals more deflection.

  • avatar

    I use nitrogen in both my GMC Van(Aluminum rims) and my Camry, my GMC Tires always leaked Air, since using nitrogen since Spring time, they have not leaked! I do notice a bit better gasoline kms on the Car too, in this area they charge $5.00 per wheel.

  • avatar
    Stephan Wilkinson

    People keep talking about “proper tire inflation” (i.e. recommended pressure) for maximum mpg. Wrong. You want max mpg, pump the suckers up. Recommended tire pressure is a compromise between comfort and mpg.

  • avatar
    virages

    Hmm, I think that tires should be filled up with CO2. Filling up the hundreds of millions of tires in the world should go a long way in carbon sequestration. In fact you should get credit for it.

    I’m thinking of selling a system where the tires are constantly inflated by the exaust…. ;)

  • avatar
    tankd0g

    People do it for the green valve caps.

  • avatar
    jthorner

    The vast majority of vehicle owners do not, in fact, check the air pressure in the tires of their vehicles at least once per month. For them, Nitrogen is a real benefit since they will spend a much higher portion of their time with properly inflated tires.

    Smart tire shops would use a Nitrogen fill at no extra cost and offer to check and top off anytime. This gives customers a reason to come back and also gives the shop a chance to do routine inspections to check things like alignment, shocks and brakes.

    As others have already said, Costco fills new tire with Nitrogen at no extra cost. Other tire companies would be smart to do the same.

  • avatar
    thx_zetec

    I’m skeptical.

    I think most leaking is from valve stems, punctures, and rim seals.

    Air is ~80% nitrogen anyway.

    Most tires don’t fail from internal oxidation.

    Also someone commented that nitrogen does not change pressure as much under heat. Not true – nitrogen, oxygen behave a nearly “ideal gases” and thus pressure change will be same under temperature.

    I think big factor is quality of rim seal. Was wheel manufactured correctly? How about the tire? How careful are most shops mounting tires,even small particle will cause small leak.

  • avatar
    ghillie

    # rpn453 :
    October 30th, 2007 at 7:09 pm

    ghillie, I believe it is mainly due to deformation of the tread mass and sidewalls. I’ve been told by a tire engineer that a tire’s fuel economy is primarily dependent on the mass of the tread. This makes sense to me since it is the mass that is continuously being deflected while driving, and less tire pressure equals more deflection.

    Thanks for that rpn453

    So it’s not to do with the increased friction between road and tire due to a larger contact patch.

    I assume it is a combination of tread mass and tyre pressure. More tread mass, more tread to deflect (so some tire will be more efficient than others) but increasing the pressure reduces deflection for any given tire.

    But would increased pressure significantly reduce deformation of the tread? That doesn’t seem likely to me. However, I can easily understand that increased pressure reduces side wall deflection.

  • avatar
    cheezeweggie

    Just another gimmick to take a bit more money out of my wallet and put it in someone else’s. I put green caps on my tire stems and I can feel the difference :)

  • avatar
    matt

    Second, nitrogen’s larger molecules are less likely to seep through rubber.

    I was going to say that Oxygen is larger because of the higher molecular weight, but after doing a quick Wikipedia search, I guess the nuclear forces make it smaller. Hm. You learn something every day.

  • avatar
    jazbo123

    The real [gaseous] enemy of tires is ozone (O3), not O2. Ozone is in abundant supply outside (along with UV, another degrader).

    Both of these factors are either in very limited supply or unavailable on the inside of tires. The argument about interior tire degradation by O2 is completely specious on a human timescale.

  • avatar
    FreeMan

    This is what I love about TTAC!

    Thanks to Michael for the great article and to the commentators for the great information. I’ve seen billboards advertising the N2, but I had no idea why, and I figured that it was mostly a gimmick, and now I know, it mostly is. Funny thing is, I was just discussing this with a buddy last night – he said he’d heard that putting ‘air’ back in to an N2 filled tire could be dangerous. After I pointed out that there’s a lot of N2 in the air, he was relieved. This just goes to show how much confusion the marketing has managed to create.

    I did just notice a local place that offers free N2, so maybe I’ll take my tires in there for a fill up – I do have one that seems to leak like a sieve, even though there’s no puncture.

    My only question – do they first draw a vacuum in the tire to get all the O2 and other gases out? If not, I’m not really getting an N2 fill up, am I? If that’s the case, then lantius‘s comment is right on – enough fill ups with the O2 leaking out equals 95% N2 content!

  • avatar
    shaker

    Great Article!

    Following Landcrusher’s comments; I think that the Federal EPA should mandate (and provide funding) for user-friendly (large, accurate PSI guages), free tire inflation at all gas stations, and TV commercials to promote their use. The “bang-for-buck” factor should be pretty high, as increased awareness/participation in the maintenance of proper tire inflation pressures (for both safety and fuel efficiency) would have fairly immediate benefits.

  • avatar
    ash78

    Landcrusher:

    See my comment above about a $9 Campbell-Hausfield air compressor from Walmart. It stays in my trunk and has a 10′ power lead to the 12v outlet in my trunk or console. About 9″ x 3″ x 6″ when packed.

  • avatar
    ZoomZoom

    Ash, how long does that compressor take to fill a tire to 40 PSI or so?

    I’m interested, because I don’t want to clutter up the garage with a big compressor, yet am concerned that a 12 V DC one would be too slow to be practical.

  • avatar
    dhanson865

    fwiw, some gas stations along interstates have free air. Though it does seem to be a rarity. I’m just going by memory but it seems to me most gas stations don’t have a working air pump. Seems like the pay ones are out of order/vandalized more often than the free ones.

    For me there is a free air pump at the Pilot Fuel Center off of I-40/Lovell RD that is very convenient from my house but when I move I might just follow ash78’s lead and buy a 12v air compressor. Since I have more than one vehicle it’d be nice to be able to deal with all the tires in one pass instead of doing them in batches.

    I suppose a cold winter day after the frost is on the ground would give you drier air if you are going to compress it yourself, though humid air is better than a noticeably under inflated tire…

  • avatar
    rpn453

    ghillie :
    October 31st, 2007 at 12:30 am

    But would increased pressure significantly reduce deformation of the tread? That doesn’t seem likely to me. However, I can easily understand that increased pressure reduces side wall deflection.

    Higher pressure will cause the tire to stay rounder. The rounder it is, the less it’s deforming. Any change in shape due to load on the tire will involve deformation of both the sidewall and tread, but the tread contains most of the mass.

  • avatar
    dhanson865

    ZoomZoom a review I googled said

    “I left it running on one of my small truck tires for 20 minutes, and it wouldn’t pump any more than 33 pounds of air”

    Someone else said it would do 5 psi in a short period.

    I guess it’s best used for emergency/light use and hit a proper compressor for high PSI use.

  • avatar
    tankd0g

    To actually fill a tire with pure, dry nitrogen, one would have to first create a vacuum inside the tire. To my knowledge, no shop does this, mainly because it’s impossible to do with a tubeless tire. So you still have “air” in your tires, with a higher percentage of Nitrogen than the outside air, but it’s still not pure. I have access to free nitrogen where I work and I have tried it in my track tires, and it does make a difference in how much my tire pressure increases due to heat, but not enough to be useful. For example, I get about a 5 psi rear tire increase after the tires are heated up on track, which means I have to either compensate for that initially or bring it in and deflate them by that much. I recorded a 2 psi difference with nitrogen. I still had to make adjustments. So what’s the point if I still have to adjust for a known constant either way.

  • avatar
    Lumbergh21

    You can get a cheap little compressor that is good for filling tires (in a reasonable time) for under $50. My wife’s brother gave her a little 12V compressor that wasn’t worth a darn. It just couldn’t properly inflate the tires on her car. The other thing to consider is for $50 you can get a small compressor that will not only fill the car tires but can put out up to 80 psi so you can use it to quickly and easily fill bike tires as well.

  • avatar
    stuntnun

    the part about the wider tire causing more friction with the ground i dont think is true so much in a cars case, i think the weight of the vehicle is just transfered over a wider area. i think its more to do with the efficient transfer of work from the motor to the ground. all the sponginess and twist in the tire cant be good for that. i know at the track 5 second quarter mile cars have under inflated wheels but thats so they dont explode when they get hot and theres more surface contact with the pavement. also i think skinnier tires would get hotter than wide tires because theres less surface area on the skinny tire to transfer heat away from it and it would also not grab as well. as for the nitrogen in a tire,i think its like telling you gatorade is better than water,maybe if your a professional athlete but for the average vehicle no.

  • avatar
    jurisb

    some of you mentioned the ill fated firestone case with ford exploders, and not the low pressure or wear and tear caused those disasters. it was caused by a simple thing- STINGINESS/GREED. while japanese counterparts of the above mentioned company made firestone tires with solid steel side-cords, american company desided to save a buck for a six-pack and make hollow cords, thus reducing their strength.thus resulted in a mass tire explosions/
    Is this hereditary?
    yes for the whole american industry, for decades most of the american companies have tried to invest as little as possible squeezing out as much as possible( see, ohv, leaf springs, trucks, trains, bikes,etc). although their r&d investmnets rank high, the real tangible outcome from them is questionnable ( for exaple, 6 billion mondeo programm, or boston bridge-tunnel 6 km lenghth of costing over 12bn, etc). And you might say i am talking bullshit here, but let`s see who will own united states in 40 years! avoiding meaningful industries for sake of easy fast profits, has made us a debt-handcuffed country. Simply as americans needs things to buy, but american companies don`t offer it, except dot coms, you have to import it. no money? that`s what chinese and japanese bankas are for! will you sell Alaska then ?
    ok, don`t inflate your tires with nitrogen, or whatever!( just to stay on topic) :))))

  • avatar
    shaker

    I’m going to start a franchise that will inflate car/truck tires with helium; the benefits are obvious, reduced unsprung weight, better “gas” mileage, lower tire temperature, and since helium is inert, less dry rot on the inside of the tire!
    I will also offer superior lubricants based on the extracts of anaconda skins. (Who’s with me?)

  • avatar
    ash78

    ZoomZoom
    I mostly use the small compressor to “top off” when the tires are low, but going from 30 to 35psi takes about 90 seconds. It’s a little quicker at the low end, so I’d guess 0-40psi would take about 7-8 minutes.

    But I’m usually in the garage and just cut it on, go check the oil, top off fluids, etc while I’m waiting. Not the quickest method to fill, but it’s also nice peace of mind when traveling. Most modern tire leaks are slow (not blowouts), so if I’ve got a slow leak far from home, I can just overfill slightly and get back on the road until I can get a patch.

  • avatar
    Stephan Wilkinson

    Unless you live in a studio apartment, buying a toy compressor is a waste of time. Get a standard compressor from Sears or Campbell-Hausfelt (maybe they’re the same thing) and you’ll quickly find out how many other uses you find for it.

  • avatar
    Ryan Knuckles

    shaker:
    Sound like a plan, but we had better higher a good marketing firm

  • avatar
    shaker

    Ryan:
    Why not Goodyear? Their blimps have been using He successfully for years! ;-)

  • avatar
    fallout11

    “Second, nitrogen’s larger molecules are less likely to seep through rubber.”

    Uh, no. Not really.
    Nitrogen’s covalent radius (1/2 the distance between identically covalent bonding nuclei) is roughly 75pm (picometers, 1 pm= 1x 10-12 m).
    Nitrogen’s covalent radius is 75pm, so the length of a nitrogen molecule (N2) is 4 X 75pm or 300 pm.
    A molecule of Oxygen (O2) is just a shade smaller, 4 X 73pm or 292pm.
    So an oxygen molecule is little less than 3% smaller than a nitrogen molecule, not enough to matter.

  • avatar
    jrphilli

    The nitrogen molecule is smaller, not larger than oxygen molecule. There does not seem to be any basis
    for nitrogen to differ greatly in leakage. The relative chemical inertness of nitrogen is favorable.

  • avatar
    ted.weber1981

    If it is free and better for the environment, and is less likely to leak, why not fill your tire tubes with Nitrogen? And somehow, I have missed all these ads- thanks Michael for bringing it to my attention!


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