Nitrogen in tires - Q&A

Our recent blog post, "Tires - Nitrogen Air Loss Study", looked at using nitrogen in tires. So far, it has generated a lot of interest. In fact, that post has received more comments than almost any other. Among the comments were many questions--more than could be addressed in a simple comments format.

Senior tire engineer and program leader Gene Petersen has compiled answers to the comments thus far, adding further insights into the testing and the results. A tires Q&A is presented below.

For further discussion, online subscribers are invited to engage the experts and other consumers in the "Tire Talk" forum.

For quick background on the nitrogen test:
Consumer Reports wanted to find out if nitrogen is worth the price for passenger vehicles, so we evaluated pairs of 31 tire models of H- and V-speed rated, all-season tires used in our tread wear test from 2006. We filled one tire per model with air and the other with nitrogen. The test was quite simple: fill and set the inflation pressure at room temperature to 30 psi (pounds per square inch); set the tire outdoors for one year; and then recheck the inflation pressure at room temperature after a one year period.

Read the original post.

Q: Were the tires installed on a vehicle? Would the weight of a vehicle have a greater effect on the loss of psi?
A: The tires were initially inflated indoors at room temperature and then stored outdoors for one year on a specially built tire stand to keep them separated. After one year the tires were returned to the indoor location and inflation was checked at room temperature. Our test was a controlled comparison with many tire models. Plus,  we did not install them on vehicles, which may or may not have been another variable.

Q: Seems to me that since the difference is so small and nitrogen is difficult to get and more costly that it is not worth the effort and the cost.
A: That's  a logical conclusion.

Q: Were the tires on new rims or older ones?
A: The tires were taken from a tread wear test we performed last year. The tires had 16,000 miles of simulated travel on the wheels, so technically the tires and wheels are used products. But I want to mention that the tread wear test ensured that the tires were well seated to the wheels.

Q: I have nitrogen in the tires on my Prius and noticed an immediate improvement in gas mileage of 3-5 mpg. Better gas mileage was the selling point when the dealer suggested the change. I'm interested to know why gas mileage was not part of the test.
A: Fuel economy is related to the tire's rolling resistance, which is a function of load and inflation pressure. High load or low pressure causes a tire to have higher rolling resistance and, therefore, lower fuel economy. If the nitrogen retains the pressure better than air in a tire, fuel economy might benefit. But I cannot think of another reason why fuel economy would solely improve based on using nitrogen in lieu of air. Overall, if you can maintain proper inflation pressure, then fuel economy will be optimum.

Q: I just thought I'd remind everyone that nitrogen makes up like 75-78% of ambient air, so air verse nitrogen should make little or no difference.
A: Yes, nitrogen makes up most of the air -- about 78% as you point out. Think about this, though: if you fill your tires with air, the oxygen is more likely to permeate out of the tires before the nitrogen and over time you end up with a higher concentration of nitrogen. I have not checked this but it seems possible.
An additional point: not all air is of equal quality. Moisture, oil from the air compressor, and other pollutants can affect tire integrity.

Q: I just had nitrogen added in our 1999 [Saab] 9-3. I'm getting roughly one mpg better than before.
A: Interesting. Maybe the tires were under-inflated before you had the nitrogen fill.

Q: The test implies the tires simply sat outside for a year and were not driven or used during that time. What good is that? Tires get used. Without testing the impact of actual wear and tear, this test is useless. Why not fill a long-term test vehicle with two nitrogen tires and two air tires and then drive it for 10k miles and inspect for wear, psi, etc?
A: The intent of the study was simply to answer how well air and nitrogen are retained in a tire. This methodology allowed us to chart the differences across more than 30 tire models in controlled conditions -- a laboratory process we would not have been able to replicate driving the vehicles. We did not explore the claimed benefits of nitrogen on limiting tire aging or look at the dynamic effect of gas permeation under operation. Those interesting topics were beyond the scope of this test. Also, wear effects would largely be affected by maintaining proper inflation pressure regardless of the gas used (air vs. nitrogen).

Q: I think we are missing some of the advantages here. First, the air loss mentioned above is 2.2 vs. 3.5 psi. That is a significant difference, even at this low inflation pressure. Also, nitrogen is an inert gas, and so will react with the rubber/chemical compounds much less, contributing to reduced wear. Another point is that nitrogen will not heat up like oxygen, so during extended highway driving you will reduce the over-inflation and wear/tear resulting from heat build-up.
A: Interesting points. Because nitrogen, in our case, is a processed gas (moisture and oil was filtered out by our nitrogen generator), you might expect better inflation control as the tire heats up under normal service vs. air with unregulated moisture, etc. And nitrogen has been shown by the government and industry to reduce tire aging.

Q: This seems like a flawed test because the tires weren't tested under "normal operating conditions."
A: Tires are designed to perform as intended with air, and the tire manufacturers tell us as much. Assuming that proper inflation pressure is maintained,  the tires will run as designed using air or nitrogen.

Q: What about daily, weekly, and/or monthly fluctuations due to significant changes in the ambient air temperatures? Would you expect that the psi variation due to ambient air temperature changes over shorter periods of time could be much more pronounced?
A: We did look at the inflation pressure over various ambient temperatures but could not find a significant difference between air and nitrogen. We are not making any claims here, but just telling you what we found. 

Q: A flawed study and analysis. And sadly quiet on the advantages of using nitrogen in heavy trucks where 18 tires need to be maintained weekly to pressures of 100 psi.
A: The positive benefits of nitrogen in high(er) service pressure applications, such as used in large truck tires, has been documented in the industry. Our test centered on passenger tires, only. We are not discrediting the use of nitrogen, but it is not a substitute for regular inflation checks.

Q: I think the bottom-line comment about being sure to check pressure regardless of air or nitrogen is key. I think the tendency would be to NOT check nitro filled tires as frequently as air filled.
A: I agree. People might think that once nitrogen is used to inflate tires that they no longer need to check the inflation pressure. Hopefully these tire blogs and discussion with our faithful readers will be a good reminder that there's no substitute for regularly checking your car's tires.

Learn more about tires and see the results from our latest tests in the Tires section of ConsumerReports.org.

Comments

[Aaron]

I'm in the Marines in aviation maintenance, and we use nitrogen to fill our tires. The reason for this is because the pressure changes less with temperature differences (which obviously occurs more rapidly in a jet flying from sea level to 30,000 feet). So during the season change there will be a higher chance that a nitrogen tire will not need to be filled as regularly during fall when it starts to cool off.

[Lindsay]

I've never checked my tire pressure. According to your tests tires only loose about 3 psi per year inflated with air. Why should I go through the trouble to check my tire pressure?

[Randy]

Lindsay - it may not sound like much, but 3 psi loss will cost you gas milage, and if it goes to 6 psi, could result in dangerous underinflation, resulting in a blowout at speed.

[Greg]

Lindsay: The test was done with the tires left on a stand. I would think that if the tires were actually under the (heavy) load of a car, plus regularly in use, that they would lose more than 3psi per year. Other sites that I've seen before claim that tires can lose up to 1 psi per month while in use.

Hence, it's best to check tire pressure regularly. Futhermore, regular checks are important to catch leaks, perhaps due to damage. It's best to find a leak early, before it leads to a serious underinflation problem or even a blowout.

[david]

under track driving conditions, air-filled tires consistently gain about 1 psi per 10 degrees F temperature increase. what change would you expect to see if using nitrogen?

[Phil]

I'd like to see you reverse the setup (switch tires) and perform the same test. This would show results based on tire variability and composition.

[Phil Sexton]

There is a notable difference in the way in which the nitrogen filled tires were treated as compared with the air filled. The nitrogen filled tires were deflated and then reinflated three times (according to your account). That could have caused a significant difference in (1) the seating of the tires on the rim and (2) the cleaning of particles from the valves. Both of those effects would have biased the test in favor of nitrogen.

[Jamie]

I work for a tire retailer and this article got me thinking about the impact of the temperature change on the pressure in the tires, which is where the biggest customer benefit to the consumer should show up. We did a simple test: inflate all tires to the same pressure - 2 with Nitrogen, 2 with Air - in the shop and then leave the vehicle outside overnight and check the pressure again. All 4 tires on a 93 Chevrolet Corsica were set to 35 psi in the shop and then the vehicle was left outside overnight. In the morning at 11:45 am (temperature 4 degrees celcius - 39 degrees farenheit) we checked the tires again. Both the Nitrogen inflated tires were at 34 psi (1 psi pressure loss over a 20 degree Celcuis change). Both the Air inflated tires were at 32 psi (3 psi pressure loss over a 20 degree change). The same pressure guage was used in all cases.

[Steve S]

That's an interesting test. But, the results are inconsistent with the science. Both sets of tires (the air filled one and the nitrogen filled one) should obey, to a first order, the ideal gas law. From your statement, I assume that the temperature when you filled the tires was 24 deg C (or 297 deg K), and the change in temperature was 20 deg C (or K). Then, we would expect the tire pressure to change 20/297, or approximately 6.7%. 6.7% from 35 psi is a 2.4 psi drop. Yet, you said you measured a 1 psi drop with the nitrogen filled tires (much less than expected), and a 3 psi drop in the tires inflated with air, somewhat more than expected.

[Brian Smallcanyon]

What happens if you mix nitrogen filled tires with air accidently. Is it dangerous or will my friend sister be okay?

[Al Hughes]

I keep nitrogen in all my tires but that's mostly because Costco, where I buy my tires, fills all their tires with nitrogen at sale and during any subsequent service. They don't charge anything extra. I guess you can say that they are building the cost of the nitrogen into the base price, but since their prices are consistently lower than any of the other chain or independent tire retailers in my area (especially if you can plan your purchase to take advantage of their frequent coupons for $60 off on a set of four) I guess I don't care.

[Winston Elston]

Team Nissan in Marietta, GA lists "Nitrogen" as a $279 dealer item on the add-on sticker. You can buy a lot of tire gauges for that money.
I would also mention that the tires on the 1957 Plymouth entombed for fifty years "...still held air..." according to an antique car magazine's blurb on the exhumation, despite the fact that the car had been reduced to a pile of rust that kept its shape almost entirely due to force of habit.
As for comments about nitrogen being more resistant to increased pressure from heating, I would refer you to the "ideal gas law" we all studied in high-school science class. If you don't remember it, the gist is that it doesn't matter what molecules are present: only the number of them, the temperature, and the volume in which they are confined.

[Francis X. Maloney]

Pure Nitrogen inflation versus compressed air
First of all it has nothing to do with nitrogen. Nitrogen is not the problem… the problem is the oxygen. Our atmosphere is made up of 78% nitrogen, 21% oxygen and 1% misc gas, but it is the oxygen that causes the problems. Oxygen reacts to temperature changes; oxygen and the moisture associated with it also cause oxidation inside the tire which is corrosive. Oxygen is a smaller molecule which permeates through the rubber faster than nitrogen. Oxygen also destroys the characteristics of rubber over longer periods, known as dry rot.
This nitrogen study that was performed by Consumer Reports was a waste of time. By not putting the tires into use or at least simulated use you have not considered the heat factor. The more heat in the tire the more pressure inside the tire, the more pressure in the tire the faster it wants to leak out. As the heat builds up in your tire so does the pressure and this is why tires explode. Case in point… Boeing 727-200 - Overheated tire exploded in wheel well after takeoff, damaging hydraulic and electrical systems. Aircraft lost control and crashed. 167 of 167 killed (Maravatio, Mexico, 3/31/86). This was determined to be a single tire that was just serviced and filled with compressed air and not Nitrogen like the other tires. The FAA now mandates nitrogen inflation is all aircraft.
As for rolling resistance… Consumer Reports can preach all they want about maintaining proper tire pressure, but the fact of the matter is we don’t. AAA reports that 85% of all cars on the road are driving on underinflated tires. If you have regular air in your tires and you’re only having your tires check when you have your oil changed you are wasting money. Ask any quick lube service facility how many cars come in for service that don’t need any air added to their tires, I’ll willing to bet it is less than 10%. With Nitrogen it doesn’t leak out as fast… end of story. Less pressure lose equals better rolling resistance which equals better MPG.
If Michelin didn’t believe that nitrogen was better for your tires why would they have a nitrogen filing station at their corporate headquarters in South Carolina free to their employees?
The government has known about the benefits of nitrogen for years. The reason for all the recent talk is that there is a relatively new process for creating small amounts (2cfm – 21cfm) of nitrogen. These new nitrogen generators are now affordable own and easy to install and operate. Prior to this process you had to buy nitrogen gas in 2000psi bottles or own your massive nitrogen generation plant like you find at most food service plants. Yes insides that potato chip bag is dry inert nitrogen, because if it was oxygen the food would spoil.
The big question is should we pay to have nitrogen in your tires. I do… but I wish I didn’t have to. I think the public should demand it from their service providers and if they don’t offer it go somewhere else. If Costco can offer it for free to all their customers and they tires are still the least expensive in town why can’t everyone else offer this valuable, money saving, safety feature for free. Auto manufacturers have recently started inflating certain models with pure nitrogen, but they are not telling anyone they are doing it. As a former employee of the National Auto Dealers Association I am willing to bet the dealer network is behind this silence.
Clemson University conducted a study of data from a nitrogen inflation field test and they concluded that the fleet got 6% better fuel economy and 50% better tire wear. 50%... WOW, no wonder the tire manufacturers don’t want us to use nitrogen. If we all start demanding it America would be a better and safer place.

[Michael H]

The aspect of "air" that is potentially not accounted for by the ideal gas law is any components of the gas mixture that are no longer gaseous at the new conditions, namely water vapor. In the overnight test cited by Jamie in which the tires were filled at room temperature and then tested after a night at 4°C, any water vapor present (as gas) in the room-temperature air would have significantly turned to liquid at 4°C, and as liquid it would not exert pressure like it did as a gas. Assuming that the nitrogen is also dried in the course of isolating it from air, it is reasonable to expect that nitrogen-filled tires would experience less pressure loss through condensation of water vapor than would air-filled tires simply due to the fact that the nitrogen contains less water vapor than air.

(An extreme case of this is sometimes used to demonstrate the magnitude of air pressure. A metal can is filled with steam and is quickly sealed, then cooled, causing the steam to condense as water vapor. Since the steam displaced the air before sealing the can, there is virtually no gas pressure inside the can after the steam condenses, and the external atmospheric pressure quickly crushes the can. This has even happened to entire railroad tank cars if they are mistakenly sealed immediately after steam-cleaning the interior.)

In the long-term tests, to the extent that oxygen is more reactive with the tire components, part of the oxygen fraction of air could be consumed by chemical reactions with the rubber. I think this is more likely to account for the pressure loss in air-filled tires than a differential leakage of oxygen vs. nitrogen. In fact, oxygen molecules are slightly heavier than nitrogen molecules (by a ratio of 32 to 28), thus at the same temperature oxygen molecules move at an average speed which is the square root of 28/32 that of nitrogen molecules, i.e. oxygen molecules move at 93.5% the speed of nitrogen molecules under the same conditions (or equivalently, nitrogen molecules move 107% as fast as oxygen molecules). As a result, if two identical tires were filled to the same pressure at the same temperature, one with pure oxygen and the other with pure nitrogen, the purely mechanical leakage of nitrogen should occur about 7% faster than that of oxygen.

Thus if air-filled tires lose gas pressure more rapidly than nitrogen-filled tires, it seems likely that this is due to the oxygen molecules being consumed by chemical reactions (such as the oxidation of the rubber on interior surface of the tire) rather than to a greater escape rate of oxygen molecules.

[Niki Zachary]

I recently priced tires. One tire dealer uses nitrogen exclusively. You have to request air. When I asked the dealer id they fill/purge three times, he had no idea what I was talking about.

What is the proper method for "nitrogenizing"? Should the tires be mounted on the vehicle and the vehicle resting on the ground?

[Annon]

@Mighael H: If the pressure loss was due to the oxidation of your wheel, you wheel would be consumed within a matter of months judging by the quantity of air lost. Permeability depends more on the molecule size than it does on molecule mass. A quick Wiki (for what it is worth) reveals that oxygen has an atomic radius 5pm smaller than Nitrogen, and a covalent radius 2pm smaller than nitrogen. Assuming the numbers are as nice as the look, this means O2 is 5% smaller than N2, and 5% is a big difference when molecules are shoving themselves through spaces where e would like for them not to go...

I would also like to reitrerate what others have said--that compressed air is quite far from ideal. Odds are, it has a good deal of water, oil and particulates which will not conform to ideal gas behavoir, so temperature effects cannot be waved off so easily.

That said, if I could ever pry the $5 per tire from my wallet to fill with nitro, I would be so stricken with guilt over buying it that I would start checking my air regularly. Seriously, just stop by Speedway once a month and you can get al the benefits for free...

[Mike]

Well I had my 2008 GMC tires filled with Nitrogen back in August at a local tire dealer (no charge) who was promoting the benefits. I know him well and he offered to put it in my tires if I was give him my opinions about it.

It was about Aug 15ish and we filled the tires to 35psi, temp was in the 80's. Last week I got my Onstar diagnostic report which showed my tire pressure at 31psi (tire pressure monitoring on vehicle). I took the same gage we used to fill the tires (compared my gage to shop gage) in Aug and it read a tick over 30psi at 20°F. So that about 5psi drop in approximately 50°. I then checked my tire pressure monitor reading after topping to 35 psi on gage and it now shows 35 psi. So it does not keep the pressure when the temp changes and that was promoted by the tire dealer.

btw-This shop changes $5/tire or its free with tire purchase. Don't ever pay for this, its not worth it.

[Philscbx]

Aaron from the Marines is mistaken on why Nitrogen is used in aircraft tires. 1. Large Aircraft tires use 200 psi, it takes tank at 2000 psi to service them during layovers. It takes 4 hours for them to cool enough to get accurate reading. So therefore the fact the gas used does not expand is false.

Others who never check their air as Lindsay claims is why I have to roll down my window and make the driver aware of a low tire before they cause an accident on the freeway.

Air pressure drop is 95% the cause at the rim to tire bead contact and valve stem.
Even on a new tire stored in a rack.

The tire shops using nitrogen as a selling tactic is a total scam and they know it.

Jamie's test of 2 with Nitrogen and 2 with air left out over night is critically flawed.
1. The direct sun is effecting the outcome to start with.
2 You would of had to have to tires under water the entire time with time lapse to show no air escaped from mounting surface.

Michael H is more in tune to what is actually going on.

Niki Zachary, AS to answer your question weather tires should be on vehicle on the ground for triple filling. A one time shot of using vacuum to evacuate the tire would be more effective. The mounted tire would stay mounted- seated on rim.

Even so, and as Winston Elston, and I have done for more than 40 years, which just goes to show that straight compressed air has been no issue. It's more on the process of how careful the tires were mounted and cared for vs any true benefits of Nitrogen.

Like I said earlier, fill 2 same tires on the same wheels of one air, one nitrogen stored under water for a month or a day. Prove the smaller gas molecules of oxygen escaped through the carcass.

[Embee]

My father purchased a new Chrysler SUV last year. I don't know if they came standard or as an add-on, but he has nitrogen filled tires. He recently received a notice from the dealership that it was time to have his tires drained and re-filled. He checks the tire pressure regularly, as you should weather you should weather you have nitrogen or "plain old air". I can't find any other info on having nitrogen filled tires drained and re-filled, except the postcard from the dealership - and I don't drain and re-fill my "plain old air" tires every year. Is there any reason why tires filled with nitrogen need to be drained and re-filled annually?

[Ricky yeo]

Is it possible to fill nitrogen air into a tire with tube in it. what is the advantages and disadvantages.

[Steve S]

Mike-

Your experience of seeing a 5 psi drop in air pressure with an approximate 60 deg F change in ambient air temperature is consistent with physics. Remember PV=NRT for all gases that obey the ideal gas law. T in the equation is in deg K. The 60 deg F air temperature change you reported is equivalent to a 33.3 deg K (or C) change, or around 10% of the absolute temperature. Hence, you should have seen a 10% change in air pressure, or 3.5 psi. This is in good agreement with your reported 5 psi loss, given that it occurred over several months, so there was some N2 leakage over that period of time also.

[Mikey]

I just bought a MAZDA. They are filling the tires with N2. We can wiki molecular radii and consider ideal and non-ideal gas laws, correct for weight differentials. It is so easy to get mired in the details and forget the facts. think about it. If I check my tire pressure and it is low I will fill my tire(s) with air, simple. The reality is that when I notice low tire pressure I'm not waiting until I can get to a Costco or book-in at the dealer. Honestly, I'm probably on a road trip somewhere or in the middle of a busy week. Why am I letting the dealer fill my car with nitrogen for $300? After arguing over the thousands, I'm not about to dicker over the hundreds, because at that point I've gone back and forth between dealerships enough to get the lowest price and that last dealership isn't even close. Adding the nitro fill to the bill is their final way of saying, aha! see, we did manage to screw you. Lets face it, we have to be prepared to bend over sometimes...

[Robert Biggs]

Have you ever filled your tires at the gas station during a warm humid/rainy day? Spray the air gun into the air and see how much water sprays out with it (or any air compressor that doens't have some sort of dehydrator). I've seen some spray enough water that it actually started to puddle and run on the pavement. I would use nitrogen just to keep all that water out my tires.

[Jay]

Nitrogen vs. air. First, I’ve gotta say that there are an AWFUL lot of people spending way too much effort on this all – people with too much time on their hands perhaps. Maybe even me. Me? OK, like half of the people on this, I have an opinion – and a few facts. Maybe the tiniest of questions, but frankly, it’s not too significant anyway. In almost any ROAD vehicle application, It DOESN’T MATTER!! If you check your tires every couple of months in the spring and summer, and every month in the fall and early winter – IF you live in an area where it gets COLD – you’ll be fine with air. (why more as it gets cold? Because the gas laws are real …. It’s IMPORTANT [here in the Great Plains anyway] to know that TEMPERATURE will affect the pressure a lot. The “rule of thumb” is that a 10-degree change will give you about a one-psi change. SO, if the tires are “perfect” at (an example of) 32 psi on Sept. 1st, at 90 F. and then only 10 weeks later … on Nov. 15th … it gets down to 15 degrees F., you’ll likely have “lost” 7 or 8 psi. If they are now at 24 psi, THAT’S FAR TOO LOW! Nitrogen will make no difference.

I happen to be a bit over 60 and, having been a “farm boy”, I was working on vehicles and tires even 50 years ago. That’s a lot of tires over 50 years. I’m well over a million miles, and have owned at least 35 different vehicles plus lots of farm vehicles and 35 years of “company cars” too. I did go to Engineering college (Chem. E for a year, then Electrical) and to Uncle’s Air Force. While spending 3 years in Germany, I got involved in racing. Yes, the Formula One teams used Nitrogen !! I ran Formula V and Formula 3 – we didn’t use anything but air. We also didn’t $pend Million$ on a car. I had a friend who was on the ground crew for the F4 phantom – and HAD worked on a “secret spy plane” .. later disclosed to be the SR71 Blackbird. The SR71 was specked to use pure Nitrogen (N2) but the F4 specs (and other craft like the C-141 Starlifter) were for N2 OR for “pure dry air”. That’s the big deal!! Normal air has moisture. Ever been to Thailand (next to the Laotian/Vietnamese border) or ‘Nam in July? It’s HOT and it’s HUMID. If you fill a BIG tire to 200 or more psi with air, (I think he said the SR71 was something like 280!!) your compressor pumps in lots of moisture. At 80,000 feet, (yea, the Blackbird!) the moisture will freeze – where? -- in a pool at the bottom. Not a good thing for tire balance when you land.

More on the moisture. That’s the reason that heat -- as in a race car tire – will make “regular air” vary more than Nitrogen or “dry air”. The water vapor expands MORE with temp than does the Oxygen or Nitrogen
.
Yes, the moisture and Oxy. may also make corrosion at the rim worse on a tubeless tire, BUT if some store sells you Nitrogen, see if and how they PURGE the thing of all the air that’s there when the tire is mounted. Some aircraft wheels have TWO valves. (1.) It’s often more handy to check pressures. But (2.) after mounting, you can FILL at one valve while BLEEDING the other for a while. Can corrosion be a problem? Well, I’ve got a 16’ “utility trailer”. I put four USED tires on the cheap USED steel wheels. That was back in 1988, when I got new tires for a pickup. I annually set them to 35 psi. NEVER has one of the four gone flat in 20 years. One does have a leak more than the other three … over a YEAR, one will be down to 25 or 26, while the other 3 are at 30 or 31 psi. Do I seem concerned? Alloy wheels can corrode / oxidize too – look at the INSIDE of your “mags” especially if you live in “salt country”. When you get new tires at 30, 40, 50,000 miles, a good shop will look and lightly grind around the bead if it’s necessary.

Some of these posts say N2 is INERT !! Not hardly. Helium. Neon, Argon (etc) – those are inert. Nitrogen is the N in N2O, Nitrous Oxide. It is the N in N2H4, Hydrazine (a cool rocket fuel!). You think Ammonia is inert? NH3 is Ammonia. There are dozens of other compounds. That Nitric acid is really mean stuff. Most all explosives too ... why is Nitroglycerine called Nitro in the business? Anyway, it ain’t inert, but IS one step less active than Oxygen.

Here’s my question for a chemist – Is an N2 molecule REALLY bigger than an O2 molecule? (and really less likely to pass – by osmosis – through a tire’s sidewall?) I knew, but looked anyway – Oxygen is HEAVIER than Nitrogen. O is the 8th element .. with an atomic weight of 16. N is the 7th element .. with an atomic weight of 14. So how is the N2 molecule bigger when the Oxygen atom is bigger?

The Consumer Reports article does show a tiny difference in loss rates, but I don’t know why. They really don’t say. These people who insist they get higher gas mileage with N? It just can’t be. If somebody can prove that the rolling resistance at a given pressure with N is less than with air (which is 80% N, of course), PLEASE tell us how that is! If you want lower rolling resistance, call Union Pacific … they can prove that steel on steel is pretty good.

One more thing – I spent 35 years in electronic communications. There are both underground cables and “transmission lines” for broadcast towers – like TV, radio stations, cell towers, and microwave radio sites – that are “pressurized” or are called “air filled”. That’s not correct. It really isn’t “air”, it’s EITHER Nitrogen or it’s DRY AIR. Years ago we hauled Nitrogen tanks to the transmitter sites to pressurize the “Heliax”, but found that the transmission lines would leak and be a big problem. Also the tanks of N weren’t cheap Some of these lines are very high voltage, but there are now “air pumps” made that have dryers to take out the moisture. With the moisture removed, the dry air works just fine. In a race car, or an aircraft, DRY air has no more temperature effects than does pure Nitrogen. In any street car, it just doesn’t matter much. If it’s free, fine, it can’t hurt, but in NO WAY would I spend money for Nitrogen. Unless they “purge” the tire in some way, you are starting with Oxygen and water vapor in there – unless the humidity in the tire shop is zero.

[Bret N]

I have a customer that claims that he is getting a 2 inch line of condensation on the outside his brand new tires that are filled with nitrogen! The line is a perfect circle around all 4 tires. Does anyone have a opinion on this or is it just a fluke? We have been using nitrogen for 2 years now and have never heard of anything like this before....suggestions???