By Roger Marble
Regarding nitrogen (N2) passing through (permeating) tire rubber more slowly than oxygen (O2) due to molecular size, are nitrogen molecules really larger than oxygen molecules? According to the Get Nitrogen Institute in their paper on N2 effusion,”The correct answer, with respect to ‘permeation,’ is yes.”
So I imagine your question is: Why don’t I support the effort to “sell” the idea of always inflating your tires with just nitrogen? It comes down to effort and cost versus level of benefit.
Maybe one way to think of this would be to imagine dropping a penny as you walk away from making a small purchase at a store. If you dropped a number of coins you might stop, bend over and pick them all up. But what if you only dropped one penny and didn’t discover the fact until you had walked to your car. Would you walk the 20 feet back to the store to look for the penny? I bet not. There is no doubt that you would have more money if you picked up the penny, but would you consider it worth the effort?
In general, tires lose about 1% of their inflation pressure each month in laboratory testing. This is almost entirely oxygen. It is also true that tire pressure changes about 2% for every change in temperature of 10° F. This is true for nitrogen or air.
I haven’t tried to run a test, but it is also true that every time you use a hand pressure gauge to check your air you let a little air out. How much air do you let out if you use a gauge to check your tires every day? Might it be 1% in a month’s time? Might it be more?
Finally, what does it cost to inflate your tires with N2? Even if you have a deal with a dealer and can get your pressure “topped off” for free, you still have to drive to the store location to get that “free” inflation.
Bottom line
IMO, the small level of benefit of inflating tires with N2 just isn’t worth the effort and cost. There is also the real negative of not checking your tire pressure simply because you believe that by inflating with N2 your tires will never lose pressure so you don’t need to check. What about small punctures or leaking valves? If you don’t check the pressure you will not learn about the leak until it is too late.
However, if you want to inflate your tires with N2, I see nothing wrong with doing that. After all, it’s your time and money, not mine.
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The reason I use nitrogen has nothing to do with permeation. Nitrogen is an inert gas. This means that there is no change in pressure with temperature increase or decrease. What I inflate a tire to is what it stays at. As a hvac mechanic I have small tanks of nitrogen handy at all times. A regulator and tire chuck and I’m good to go. Nitrogen is cheap and handy.
Sorry, Glenn, but all gases fallow the gas law, PV=NRT, where P, pressure is directly proportional to T, temperature with a constant V, volume. And don’t forget, air is 80% nitrogen and about 20% oxygen.
I disagree. The reason we use nitrogen for leak checking refrigeration lines is that it will not change pressure with temperature change. If I leave a line pressurized to 400 lbs on a warm afternoon and come back on a cool morning and it is still at 400 lbs I know I have a sealed and leak free system. May have a 30 to 40 degree drop in temperature overnight but no change in pressure.
The reason to use nitrogen is because it doesn’t introduce contaminants like air would for HVAC or tires. Race tires don’t want water from air. It is also inert and has a quicker heat dissipation but it does expand and contract as all gases do but a small volume appears not to change. If you had very sensitive gauges accurate to 1/100 of a pound you would see the change.
Good discussion, Roger. As I said in reply to Glen on the temperature/pressure relationship, air is 80% nitrogen and only about 20% oxygen ( a couple of other gases like CO2, Ar, etc). So as you say, given the permeablilty difference and only 20% oxygen, there is not much gain with pure nitrogen. But also as you say it can’t hurt and its not my (or your) money.
Glenn, sorry but all gasses follow Boyle’s Law and their pressure in a constant volume system will increase or decrease as the temperature increases or decreases. However, there can be big volume changes as a gas condenses to a liquid state around its vapor pressure point. That’s how refrigeration works, but there’s no pressure change from this phase change. The liquid/gas phase change is the result of the pressure change, not the other way around. I took classes on this back in college for engineering: https://en.wikipedia.org/wiki/Boyle%27s_law
Yep, PV=nRT is a scientific law, not just a theory.
Why do NASCAR drivers use nitrogen in their race cars if there is no advantage? I usually buy my tires at Costco and they put nitrogen in the tires they sell which I find has helped my trailer tires pressure drop better than than just plain air.Many tire dealers,like the monopoly we all know about in the Pacific Northwest,won’t use nitrogen because they are too cheap to install the equipment. But…there is no substitute for checking tire pressures every time you hit the road.
When I used to buy tires from Costco, they would inflate with them nitrogen. That’s fine if you always have Costco nearby to keep the pressure up. But, once we leave town, that’s the end of finding a Costco – at least where WE travel. Then I’m filling the tire(s) with a normal pump – and everyday air. So even if it’s a great idea, it doesn’t work very well for my lifestyle.
By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere.
https://en.wikipedia.org/wiki/Atmosphere_of_Earth
Personally I have questioned for years what the purpose of putting nitrogen in tires might be since the air we normally put in is about 80% nitrogen anyway – what difference could it make? And why would NASCAR worry about air loss when the tires aren’t even on the car more than about an hour or so? The whole thing just seems pointless.
I thought “Nitrogen inflation” was a joke like “changing your summer air for winter air”… Didn’t realise anyone was actually selling this as a serious thing. Thanks for the laugh!
My initial reaction to filling tires with nitrogen was another scam. Now after hearing all the “pros” and “cons” I’m convinced. It is a scam commercial vehicles, trucks, buses, etc. run 100,000+ a year, if their was a significant difference between n2 and air they’d be using it. At $400 per tire times 18 anything they can do to save money over the long haul they do it. Race cars use it, I don’t know why, as Roger Marble said pressures change with heat on either one, airplanes use because the different temperatures at higher altitude can drastically change, but here on the ground it’s not going to matter. It’s basically a means to get more money out of your pocket. I remember “filling stations” had signs saying “Free Air” now you pay 75 cents to put air in your low tire.
In California, FREE air is still FREE, even if they want to charge you – it’s the LAW!! Remind them it’s the law and that you want free air!
Oxygen is a highly reactive gas. Nitrogen is an inert gas, so is non reactive. The 20% oxygen in standard air does cause some reaction with the rubber inside a tires. The rubber will degrade more quickly with oxygen in the mix. Presumably your tires will last longer if you inflate with nitrogen.
I have not seen studies that show how much degradation you get with oxygen versus nitrogen. Has anyone seen any scientific research on this?
From scientific literature and Wikipedia…”Ozone-resistant elastomers include EPDM, fluoroelastomers like Viton and polychloroprene rubbers like Neoprene. Attack is less likely because double bonds form a very small proportion of the chains, and with the latter, the chlorination reduces the electron density in the double bonds, therefore lowering their propensity to react with ozone. Silicone rubber, Hypalon and polyurethanes are also ozone-resistant.”
Few non-tire engineers realize that today’s tires have a layer of one or more of the above listed “Ozone-resistant” rubber on the interior surface. Look at some old tires sometime and you will see the interior is probably softer and more pliable than the exterior of the tire. Remember Ozone is much more reactive than molecular O2 in the air.
Doesn’t matter to me as I have an air compressor to use with my Motorhome. Wouldn’t mind having them inflated with nitrogen but after that, I would only be adding air.so it would become moot, I would think. Now it would be great in my bicycle tires.
The key for me is the fact that “N” (Not N2) is DRY! I live in FL and every shop air hose here has water dripping out the end of it.
Shrimpy, you might want to review THIS information. or we could simply agree to use N and N2 interchangeably.
The dropped penny is my senior exercise program.
I always use a 78% nitrogen mixture to air up my tires it is easy to fine I have a machine in my garage that I can use at a 12 V one in my car that I carry with me. I have found it works great. If the oxygen molecules leave in the nitrogen stays pretty soon I’ll have it all nitrogen anyway.
Ditto
Exactly! This information always seems to get lost in the conversation. 🙂
😊😊😊😊😊
Great reply Terry, and truth of fact.
When I purchased my fifth wheel in 2015 there was a sticker on the side advising Nitrogen had been used to inflate the tires. The problem I have is the source of a nitrogen pump in my neighborhood. My mechanic told me the best thing I could do for my tires would be inspect them regularly and keep them inflated to the factory specs. He said Nitrogen would be nice if it were available but it’s not so I use my portable air pump to inflate my tires.
One benefit that I have personally found with Nitrogen is tires run cooler. I ran a company the last 10 years which we had 3 trucks (F350) and 3 trailers(8K) and had the drivers check temperature at every fuel stop to monitor the bearings, brakes, and tires. Tires with Nitrogen were consistently 8-10% cooler on hot days? Did not intentionally use nitrogen, it just came with the trailer and new tires.
Dave Solberg
Nobody
mentioned the air in the tire before filling the tire.
Do you know anyone that evacuated the tire,if thats even possible, before taking if to working pressure? I don’t think so. All those cubic ft of plain old air contaminating the nitrogen!
Normal atmospheric pressure is 14.7 PSI / 1 bar, so every time you increase the pressure 15 psi / 1 bar you add that same amount of volume. 15 psi = 1/2 N2, 30 psi = 2/3 N2, 45 psi = 4/5 N2, 60 psi = 5/6 N2, 75 psi = 6/7 N2, 90 psi = 7/8 N2. Some places will fill and empty and refill the tire so a 30 psi car tire would be 2/3 N2 on first filling then 8/9 N2 on second fill up.
Rodger, I agree with your view of N2 in RV tires. Should an RV owner want to
follow the N2 practice when they get the new coach home the cost will become clear quickly.
Believe what you want. I’ve been using nitrogen in tires for 30yrs. in my racing activities and due to that I’ve seen the advantages, that’s why I use it in all my vehicles.
nitrogen for tires = scam.
I am a longtime BMW owner as well as RVer. My BMW dealership stopped using nitro in my vehicles tires because there was no significant performance advantage over regular air. Plus, there was no cost benefit to speak of. I tend to believe BMW on technical matters such as this.
Costco, which always has the best tire prices, fills new tires with nitro. However, even though they will check and adjust tire pressure I’m not driving across town when I can easily adjust tire pressure at home. So, over time I’m increasing the oxygen level.
While I agree that there is only a small benefit to lower pressure loss of N2, you shouldn’t overlook the benefits of not having O2 diffuse through the tire and resulting oxidation of rubber and metallic products that negatively affects endurance. This would be especially true for trailer or RV tires that can go 5+ years before replacement.
You mean to tell me the Get Nitrogen Institute recommends putting nitrogen in my tires? Wow, there’s a surprise. I
The reason Nascar teams and other race teams use N is that it is dry, as in no moisture in it. The more moisture in the tire air the more variable the pressure gain in the tire is and the race teams taylor their handling with their air pressure. With humidity being a big variable dry N means that they know how much air pressure is going to be gained in a tire when hot. Some racing organizations allow bleeder valves where a tire will bleed excess pressure during the race leaving the pressure the same as the tire heats up. If you check your pressures regularly I think N is a waste as street tires never get as hot or need to get to a exactly right pressure as race tires.
Tongue in cheek here… Use helium and make the RV lighter.
Good idea, dale. Maybe that would help make the potholes a little smoother to go over (instead of through), also. Have a good night. 🙂 –Diane
Funny idea Dale, if Helium leaks out of my tires as easily as it does party baloons…😵💫
If you google Helium, you will find out we are running out of this special gas. Soon, no more chipmunk sounds😁
Normal atmospheric air is already 78% N2. By constantly inflating your tires with this air – if the O2 tends to permeate out of the tire, that means it is automatically leaving behind the N2 – meaning the % of N2 in tires will naturally increase anyway.
I know that some shops promote using pure N2 as a benefit, but with normal air already at 78% it seems that N2 promotion is more a marketing tool than anything else.
Race cars and airplanes, yes, other than that just an “upsale”.
If other gases seep out of the tires and the atmosphere is majority nitrogen after adding air to your tires over time your tires should be filled with nitrogen. The only real benefit of nitrogen is the outrageous price dealers add to the price of a car to line their pockets.
Nitrogen in tires is by no measure “new.” Aircraft are by far the most prolific users. But cable companies are near the top as well, but likely not for the reason one might think. Nitrogen is used to remove other gasses. Aircraft and cable companies need to get rid of moisture that can cause many problems. Since the air we breathe is nearly 80% nitrogen, we already benefit from the traits already mentioned, to a great extent. As for tires… if you let all the air out, then fill, you still have a significant volume of good old air in the mix, as the tire does not collapse when emptied. IF, someone finds a cheap way to draw a vacuum on each tire, to remove all air, then fill with pure nitrogen only, and do so for $2 per tire. I will be first in line, until then, this person will settle for 80% for free.
One huge single-brand dealership in the midWest does a hard sell on Nitrogen in all their ads, including YouTube videos. I’d have to be desperate to buy anything from them.