There is a spreading belief that if you put Nitrogen (instead of regular air) in your car tires, that you will get better gas mileage. The reasoning behind this may be sound, but the facts on which the reasoning is based are not correct. Therefore, the answer is no, it is not advantageous for the average person to use Nitrogen in their car tires. On even more detailed examination, it maybe that regular air is better than Nitrogen for most people. Nitrogen is in fact used in certain tires, and there may be a good reason for that, though the information I have is probably missing something. In other words, it is all rather complicated. The short answer is, don't bother with the Nitrogen, but there are some interesting details:
First, note that Nitrogen (from a Nitrogen tank) is all Nitrogen, while "air" is about 78 percent Nitrogen, with the rest being mostly Oxygen but also some other stuff including a variable amount of water vapor. In certain specialized uses, such as in airplane tires, Nitrogen is preferred because it lacks the water vapor, and thus, contributes less to corrosion of metal parts. I suspect there may be more to it than that, but the point is, using pure Nitrogen from a compressed Nitrogen tank means a pure gas and thus whatever other issues one might have with regular air would be obviated. Car Lift Four Post
The argument for using Nitrogen in your car tires is this: Air and NItrogen would compress at different rates depending on temperature, with air being more squishy than Nitrogen, and that would cause your tires' pressure to vary more with air than with Nitrogen. Indeed, having more variation in tire pressure is bad because there is one ideal pressure; more variation means that the tires will be at the idea pressure less often. The idea that air and Nitrogen compress differently is predicated on the assumption that Nitrogen has a single and more ideal compression dynamic than air.
However, this is probably mostly not true. Air is mostly Nitrogen, the rest of the air is mostly Oxygen, and Oxygen and Nitrogen have about the same dynamics with respect to compression and density and stuff, according to Physicist Jerry Artz.
Now, since I'm a skeptical skeptic, and not just a skeptic, I'm going to suggest that even though all this is true it is quite possible, in fact likely, that the water vapor in "air" is much more dynamic in terms of pressure than Nitrogen or Oxygen, and thus, variation in pressure of the tire contents based on temperature may be measurable if there is enough water vapor in there. I'm thinking this is most likely why Nitrogen is used in certain tires. That is, however, merely a hypothesis at the moment. I'm offering this guess because I think it unlikely that corrosion is a question in racing car tires, yet racing teams often use Nitrogen. Anybody out there know the answer to that one?
So, on one hand, the suggestion that Nitrogen is better than Mostly Nitrogen and Stuff Like Nitrogen and a little bit of other stuff mixed together is probably very much over stated. Yet, the idea that pure Nitrogen and randomly sampled air are exactly the same is highly unlikely. Having said that, the degree of difference between "air" and Nitrogen is probably not great.
And, most important of all: If you want to make the air pressure in your car's tires ideal, the elemental and molecular composition of the gas you put in there is far, far less important than the process of checking your tire pressure regularly (i.e., weekly) and maintaining it. The variation over weeks of time from minor leakage (and there is minor leakage in a perfectly good tire with a perfectly working valve) is greater, probably, than the difference between Nitrogen and air.1
Which brings us to the final and possibly most important point: Nitrogen can sneak out of the leaks more easily than Oxygen, according to Professor Artz. Therefore, filling your car tires with regular air then ignoring them, which is what you actually going to do, is better than having Nitrogen put in there at your local service shop or Wallmarts, then ignoring them.
And, really, there is a better way to save on gas: Get a more efficient car and drive less.
_____________________________ 1Also, while you are checking the air in your tires every week, could you also please drain your hot water tank annually and check with a physician before starting a new exercise program? Thank you very much.
Drawing of Nitrogen from Wikipedia.
In addition to the corrosion issue, an airplane tire will be subjected to temperatures of typically -50 to -60 Celsius at cruising altitude. Any water vapor in the tires will condense out at those temperatures. I'm not sure exactly what the effect of that would be, but that's probably not a good thing.
You are correct about your assumptions as to why nitrogen is used in race cars. It's moisture content is consistent which means that the data on air pressure adjustments and tire temperatures is consistent. On high speed ovals, in particular, very small pressure changes can have quite large effects on the car's handling. The cars often have very little suspension travel and the tire is a spring. Pressure adjustments of .5 psi or less are often made. This level of precision requires the consistency of nitrogen.
Motorsport can be a very nerdy endeavour.
In passenger cars I actually consider nitrogen to be dangerous as many people who have it are under the impression that they now never have to check their tire pressure. Regular checks with regular air is all that is needed.
Unless the water vapor in air condenses, regular old air, with all its various gaseous components, will act exactly the same as pure nitrogen with respect to its pressure variation with changes in temperature. This is certainly true within the range of pressure and temperature experienced by a tire operating in normal conditions (yes, yes, whatever that means) on a regular, civilian, ground vehicle on the surface of the Earth. Even if the water vapor condenses, the effect on pressure will be negligible in the real world. As to corrosion, maybe, maybe not. But, for what it's worth, I have never had a tire or wheel fail because of corrosion. As you say, it's far more important to check the tire pressure regularly and as often as necessary.
The bottom line is this: it's not worth paying extra to get pure nitrogen in your car's tires. Any benefits are theoretical and you will never, ever see them in normal use.
For racing, getting the correct air pressure correct is important. Since nitrogen from a tank has essentially no water vapor, the increase in pressure as the tire heats up is predictable. The water vapour in compressed air makes this increase in pressure unpredictable since the water may be liquid when you check the pressure, but vapour out on the track.
How hot does it get inside a race car tire? Or,for that matter, an airplane tire?
I wrote on this a few years ago when I was still on Wordpress and it's still one of the busiest posts I've ever created.
The comments thread is full of both sides of the argument and proponents of nitrogen in tires can be very adamant on their position to say the least. I'm also convinced that some industry reps have commented on the post as well, with their insistence that nitrogen is better. Several of these posts have a few things in common: they're lengthy, technical, and completely anecdotal ("I haven't had to add air to my tires in 3 years; I get on average 10,000 more miles on my tires...â etc). I've actually opted not to approve a couple of these comments which seem most like industry shills.
But perhaps I'm overly paranoid and they're just nitrogen proponents who take their views seriously. Either way, I predict this will be a busy thread for you!
Haha hahahaha hahaha ROFLMAO!!! lol.
.. ah... just came back from your post. I love that bit about the fiery crashes!
The only thing that seems "true" is that oxidation would be less in an environment ... without oxygen. But, I doubt tires "oxidate" at all ... i mean, getting rid of old tires is a huge problem. If they "oxidated" we could just leave them in a field and they'd go away. They do oxidate when the catch on fire of course. Which brings us back to those fiery crashes....
It doesn't get that hot inside (or outside) an airplane tire. Race car tires probably get much hotter than airplane tires and even then, they're really not that hot or else you would have issues with combustion and you would have to significantly underfill them then warm 'em up to get to the desired pressure.
Filling tires with N2 is a bit like those oxygen-free gold-plated Monster Cables (well, except that Monster Cables is 100% bullshit but as people say, nitrogen has actual niche uses).
You can use dried air of course, but in many cases buying tanks of nitrogen is less of a nuisance than maintaining the dryers.
I actually had a lot of fun writing those posts -I think I did three. It started when I bought my wife a new Ford Escape and they tried to sell us on their nitrogen tire service package. It was the first I'd known about nitrogen as an addon product for automobiles, so I wasn't really read up on the topic, but I remember asking the sales guy, "uh... isn't air mostly nitrogen anyway?" He, of course, was caught off guard and said he didn't know!
So we passed on the nitrogen and he didn't ask again. I read up on it after that, thinking this seemed a bit like "Monster Cables" the way it was marketed.
I learned a bit though. Nitrogen is a diatomic molecule like oxygen, but one that's a bit larger than oxygen, so there's some grain of truth to the idea that it might not leak as fast as oxygen if the hole it's escaping from is smaller than the nitrogen molecule but larger than the oxygen molecule.
With regard to the oxidation claims, most of those making this argument are pointing out that the metal in a rim is exposed to the pressurized gas inside the tire, and this is where opportunities for oxidation is. I just don't think the rate of oxidation is that significant since tires are designed to be worn out. If I were planning to fill my tires then park my car indefinitely, I'd probably want nitrogen.
If nitrogen were free, I wouldn't care if it or regular air was pumped into my tires. But in every case I've come across, it's an addon service or aftermarket item. This is where car dealerships make their money, to be fair. But at least I can readily see/feel the benefit of window tint or a racing stripe (my eyes hurt less with the first and the car goes faster with the second -okay... maybe it doesn't).
Reading your post is the most time I've put into the thought about 100% N2 in passenger car tires. I immediately dismissed it as a marketing gimmick, and nothing more. Rationally reasoned or not, I don't care. There are a thousand things that affect overall efficiency that it's just ludicrous to optimize tire air composition.
Stoplights vs. round-abouts: now there's a worthy efficiency discussion.
The operating temp for DOT-R tires is 180 to 200f. It would be hard to get street tires that hot(and not get arrested.
So ... we're never going to get incidental condensate to turn into blistering steam that will shoot up the compression in the tires.
Why do race cars and airplanes use Nitrogen then? Are they just being superstitious, or have they bought into the woo, or is there something we're missing?
Or, do they even really use Nitrogen for realz?
The issue with air in racing tires is that the water vapor content of air varies from Montreal to Malaysia (and places in between). Using a gas with a known composition makes it easier to predict the tire pressure when they come up to temperature, or so the story goes. I don't think they actually use pure nitrogen, so it may just be air that's been dried and filtered.
Re the aviation end of it (not an expert, just an interested layman), there are reasons to use nitrogen. Tires on heavy aircraft are inflated to much higher pressures than even heavy trucks (~200 psi?), so if you used air, the partial pressure of oxygen inside the tire would be something like 3 atmospheres. There are foreseeable circumstances such as an aborted takeoff where heat from the brakes would cause the tires to ignite, and three atmospheres of oxygen would be an undesirable accellerant. And tires burning on the inside with possibly no external signs would be a danger to the vehicle, contents and surrounding property. The rims are provided with fuse plugs which will deflate the tire with excessive heat or pressure.
On race cars, if tire pressure is so important, I'd think the lack of water is the key thing, rather than lack of oxygen. And don't discount superstition and head games either, psychological advantages are still advantages.
As far as aircraft go, the brake systems are usually a multiple disc type brake located within the inner diameter of the rim. They get very hot during emergency stops, especially with a heavy aircraft. Most commercial airliners have a warning light that comes on when the brake hits a certain temp (from a quick google search it seems most will throw a warning light at 4-500C)
Back when I was an aircrew member on a large military aircraft a brake locking, aborted takeoff, or other type of heavy weight emergency stop often required an emergency egress. We would have to avoid getting anywhere near the tires in the plane of the axles as the tires would occasionally explode. Ground crews would test the hubs with a "crayon" with a specific melt point to determine when it was safe to tow the aircraft away. I think they tested at 600 and 900 degrees.
It's very rarely an issue, but I could see the benefit of using N2 as somewhat cheap insurance. I would guess that proximity to the brakes and conduction from brake to wheel could account for significant heat, after all F1 brakes glow yellow hot under hard braking.
Greg: Road use max tire temp is about 75C. Formula One optimal temp is 100C, but they will work up to 160C. Which is why tires are heated before being put on and why the first lap after new tires is slow.
OK, so water laying around in the tire that got there from basic air being put in the tire, condensed from vapor, will turn into steam in a Formula 1 tire. That would result in a significant increase in pressure of an uncontrolled or at least unpredictable amount.
I imagine that aircraft tires spend most of their time in flight well below freezing (on commercial jet liners) and that air added to those tires now and then would produce a buildup of water. I'm not sure how hot those tires get, but they might get a little warm sometimes:
http://youtu.be/E0kjZ3L9LE8
Nitrogen if overcharged or not offered free with new set of tires, then Nitrogen inflation could be seen as a scam. Most tire and car manufacturers have tested and approve the use of nitrogen. Many local tire shops down play the benefits they, first donât want to invest in a machine and want/need to sell tires. Michelin factory in Greenville, SC offers nitrogen inflation station for their employees. Costco offers nitrogen free when you purchase tires. Do you think they would invest 8-10k per machine at over 400 tire locations if it didnât have some merit? Costco self insures their tires and majority of people donât check psi or rotate as recommended so they have found better performance less failures with nitrogen. Costco sells millions of tires per year. Jay Leno uses in his entire car collection, Google and watch the video. Lance Armstrong and other tour De France riders use Nitrogen. A bicycle tire with what little volume it has why would they go to the trouble if not for the benefits. Nissan GTR is shipped from factory with Nitrogen. Volvo has inflated all their spare tires with nitrogen for years. Most spare tires I have checked are severally underinflated never checked a Volvo yet though. My opinion and experience using Nitrogen has been positive. Yes regular air would do but I opt for the better inflation media. Nitrogen inflation is obviously not for everybody Some people use synthetic oil and pay 3-4 times more where regular oil would do a sufficient job but opt to pay extra for better lubrication. Some people pay extra for premium coffee or water too. I do a part time business a car cruises and have done hundreds of tires with positive feedback on better psi retention, handling improvement etc. Some have gone over 2 years with no psi loss where they would need to top off using air. I charge $20.00 for 4 tires and many times let customers try before they pay. I havenât lost a sale yet due to Nitrogen performance. White wall tires yellow due to the oxygen that seeps through the sidewalls. My best experience is an independent trucker owner operator. He and his wife are a team that travel 5k every week long haul. Using same brand of tires they average 300 to 330k on driver tires. I put in nitrogen in a new set they got 475k. During that time he did not need to add any nitrogen or rotate tires as he did using air. The tire shop said he could sell the 475k tires to a local trucker and still had some life. I put in my neighbors riding lawnmower where he after winter had to air up tire and during use several times now once a year with nitrogen. Wal-Mart has tested and converting their fleet to nitrogen. Many other trucking companiesâs have done side by side test and have experienced better tire life, less failures and small mpg increase over air. Nitrogen out performs air whether in an airplane (federally mandated for safety), racecar, military vehicles, motorbike, truck or bicycle tire. Nitrogen inflation will the standard in the future and should be offered free hopefully.
Greg, Iâm not a scientist or have a degree just seeking professional help. Late model cars with a TPMS system should last longer with the absence of less moisture. An average TPMS indicator in ideal conditions is 6-8 years as I hear, so if you minimize the water introduction into the tire it should have a chance to meet that goal or exceed vs. a moisture laden environment. Would you concur?
For normal, long-term use of automobile tires, nitrogen reduces oxidation on the rubber compound on the inside of the tire.
Passenger car tires are inflated to a range of 30 to 50 psi gauge. That translates to about 45 to 65 psi absolute. So if compressed air is used to inflate, the gas inside the tire is three times richer in oxygen than the gas on the outside for the purpose of supporting oxidation.
The rate of oxidation is also proportionate to the square of the operating temperature, IIRC. Normal usage in the summer will see passenger car tires exceed 200 deg. F. This is not surprising when you consider that they can have resting temperatures of 120 to 150 deg. F, depending upon their location. E.g., in direct sunlight.
Oxidation, often referred to as dry rot, is manifested externally in the form of cracks and discoloration in side walls and tread. External deterioration of the rubber is accelerated by the effects of sunlight. Internally, it is accelerated by the relatively oxygen-rich inflation gas when normal compressed air is used.
Obviously, cracks in a tire are not good, as they increase the likelihood of catastrophic failure, i.e., blowouts. They also promote slow leaks.
An argument can be made that by inhibiting oxidation the integrity of the tire is extended and the likelihood of slow leaks leading to an under-inflated condition is reduced thereby increasing mileage potential.
The obvious conclusion is that if you drive enough to wear-out a set of tires every four years or less, nitrogen will not provide much advantage because the tires will be replaced before the oxidation becomes significant. However, if you are like me or Jay Leno, and do not go through tires all that quickly, nitrogen will extend the service life by reducing oxidation.
As to increasing mileage, that's not very likely.
By the way, a tank of nitrogen and a regulator valve will set you back about $400 and can be purchased at most any welding supply company.
One of the reasons for using nitrogen in car tires is that it keeps the steel radial belts from rusting. The reddish tinge seen on the sidewalls is not always or only brake dust.
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