Tires - Nitrogen air loss study

Filling tires with nitrogen rather than air is becoming a common practice in the replacement tire market. This service offers tire dealers another avenue for making money while also promoting safety. The claimed safety benefits often include the potential for reducing air loss compared to an air-filled tire. Maintaining proper inflation can help prevent tire overheating; promote optimum tread life; and reduce rubber aging and wheel corrosion. The use of nitrogen in large truck fleets and the commercial tire industry are well documented and support these claims.

The National Highway Traffic Safety Administration (NHTSA) has seen reduced aging of tires filled with nitrogen. Though the data does support that passenger car tires could benefit by all the claims made for nitrogen, tire manufacturers say that they already design tires to perform well with air inflation. And while nitrogen will do no harm, manufacturers say that they don't see the need to use nitrogen, which generally adds $5 or more per tire charge.

Consumer Reports wanted to find out if nitrogen is worth the price, so we purchased a Nitrogen Inflation System and checked out how well the inflation held up over a one year period. 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.

The tires were filled and deflated three times with nitrogen to purge the air out of the tire cavity. We also used an oxygen analyzer to be sure we had 95-percent nitrogen purity in the tire--the claimed purity limit of our nitrogen system, which generates nitrogen gas from ambient air.

The test started on September 20, 2006 and the final measurements were taken on September 20, 2007.  The results show nitrogen does reduce pressure loss over time, but the reduction is only a 1.3 psi difference from air-filled tires. The average loss of air-filled tires was just 3.5 psi from the initial 30 pressure setting. Nitrogen-filled tires lost an average of 2.2 psi from the initial 30 psi setting. More important, all tires lost air pressure regardless of the inflation medium, so consumers should check their tires' air pressure routinely. No evaluation was done to assess the aging claim.

Bottom line: Overall, consumers can use nitrogen and might enjoy the slight improvement in air retention provided, but it's not a substitute for regular inflation checks.

--Gene Petersen

Added 10/11/07:

There has been great interest in this topic, as evidenced by the comments. Among the user posts are many questions—more than could be addressed in a simple comments format. We have posted a "Nitrogen in Tires Q&A" directly answering many of these questions.

Read the latest tire Ratings and advice. Discuss Tires in the Consumer Reports forums.

Comments

[Geri Rhodes]

Would it be possible to put C02 in tires as a way of sequestering it? What would be the effects on the operation of the vehicle?

[Mike Demers]

The missing piece of information? What was the purity or percentage of Nitrogen in the tire when all of these "tests" were performed? Like every other product, their are different levels of equipment and procedures for filling a tire with Nitrogen. The tire MUST have 95% or more Nitrogenn content. I see no discussion of the Nitrogen percentage in the above tests or personal expierences. Any reputable provider of Nitrogen will have a guage that can show the percentage of Nitrogen in the tire. The guage attaches to the valve stem of the tire, giving a real reading of Nitrogen purity. If your Nitrogen provider does not have a guage--you may be paying for compressed air! Independent blind tests by large fleet showed a significant increase in fuel mileage and tire life, when tires were properly inflated with Nitrogen. Not all Nitrogen services were created equal--95% purity or more is a must. If you check you tires every week, and fill with DRY compressed air--you will gain no bebefits. But, newer vehicles are going more miles between oil changes---sometimes 6 months and 7,500 miles. These long service intervals really demand Nitrogen in the tires. So a proper test needs...
1. 1 car with one front and one rear tire filled with Nitrogen.
2. tires moved side to side (some cars have different pressures front to rear, every 2,000 miles
3. Nitrogen content at least 95% in the tires
4. drive 8,000 to 10,000 miles
5. monitor the pressures at the beginning and end of the test
6. record the differences of pressures after 45 minutes of driving in hot weather
7. check tire wear at end of test
Will someone run a proper test? Or do we listen to more discussions with little facts or standard prodedures?

[Robert Treadway]

I think the CR test did exactly what is was intended to do: test the loss rate through the porosity of the rubber tires. The test was only intended to see if N leaked out faster than O2, under constant conditions. None of the temp fluctuations, driving conditions, "placebo effects", etc., can be included, because they cannot be held constant. The test showed a very small difference in pressure loss, which is all it tested for. You can extrapolate this to real world conditions: say you lose 3psi a month with air, then you can assume you would lose 2 psi a month with N.

The biggest (or only) benefit from N use, in my opinion, is the increased life of the tire casing, enabling it to be re-treaded 2 or three times, a cost factor in truck fleets. The theory is that the oxygen permeating the casing will eventually cause the steel plies to rust and fail. Joe consumer who replaces tires every 6 years will see no benefit. O2 in air and water vapor can rust the rim at the bead, causing leaks, but Joe consumer only keeps his car 6, or 10 years maybe?

[Fred Flintstone]

N sure sounds like another money making gimmick for the tire installers. A difference of only 1.3 psi air loss over a year's time is absolutely nothing. You should be checking your air pressure every 2 weeks anyway. Buy N for your tires and watch the mechanic laugh at how dumb you are behind your back.

[Steve S]

To Doug-

My comments about the percentage of N2 in a tire increasing was based on filling the tire, and topping it off, with normal 78% N2 air, as I stated. Yes, you're right that if the tire had been inflated with 95% or purer N2, then topping off with normal air would increase the percentage of O2 in the tire. However, that was not the scenario I described.

[Billy G]

Only a fool would believe that inflation with nitrogen would improve gas mileage 3-5 mpg. Well a fool and their money are soon departed.

[FRE]

One can, for little more than $100, buy an air compressor to keep in the garage. That makes it easy an convenient to keep tires properly inflated. With nitrogen, you have to go to a special out-of-the-way place during business hours to check the tires, so it will surely be done less often. That's why I have an air compressor to inflate my car, bicycle, and motorcycle tires. That also makes it possible to check the tires while they are cold.

[Don Lipman]

The atmosphere is already 78% nitrogen, on average, is it not? Therefore, by putting "pure nitrogen" into your tires, you're adding little additional nitrogen beyond what would otherwise be entered,

[Bill Babis]

Its just a money making gimmick. I suspect most of these increased mpg claims are due to a PSI change rather than the nitrogen. As far as 95% nitrogen not reacting with the tire rubber as much as 78% air, may be a valid claim but statistically meaningless. Unless you drive on a different planet than me, you have good old 78% nitrogen air reacting all over the surface area of the tire on the outside. Just check your tire pressures regularly and you'll save plenty of money not to mention whatever someone wants to rip you off for nitrogen.

[Bill]

The hypothetical MPG increase by using nitrogen in tires would be easily validated or refuted if Consumer Reports would fill the same tire once with air and once with nitrogen. In each case they could put the tire on their rolling resistance measuring machine. Then we'd know if there was a difference or not.

I don't see why there would be a difference but empirical evidence frequently surprises me.

[Neil Fichthorn]

I just drove from FL to NJ, a bit over 1200 miles with side trips. In the fall when going to FL, I got 23.9 mpg; this week I got 27.1 mpg. Driving speeds were about the same and vehicle weight about the same. Three things were different: first, I had nitrogen in the tires; second, I inflated the tires to 35psi instead of the recommend 33psi; third, I used only gasoline without ethanol. I'd do it again in a heartbeat! Which of the three made the major difference? I don't know, but it is a factual test done within the last two days and I feel the nitrogen was worth it.

[Paul]

No ethanol will make the biggest difference in the mpg. Ethanol though Env-friendly contains less energy than gas and therefor takes more to do the same amount of work. Second would be the pressure. Increased pressure means less rolling resistance. The engine does less work to move the car. Last would be the Nitrogen.

[Olen Soifer]

I have to laugh at people who spend $30-40 to fill their tires. Sorry, but I think it is a joke and anecdotal evidence is not reliable. Unfortunately, no-one wants to admit that they were "taken", so the tendency is to see a benefit that doesn't necessarily exist.

In terms of the specific claims:

First, nitrogen, being a smaller atom and molecule than oxygen, should leak thru the rubber tire quicker than oxygen.

Second, the comments about perfect gases and the laws of thermodynamics do not vary because you are trying to justify having been ripped off by a fraudster.

Third, as someone above has said, take a look at the inside of an old, hard, deteriorating tire. You will find that it is quite soft and flexible...meaning that the deterioration comes from exposure to UV, ozone, possibly other exposures, not from the oxygen inside the tire.

Fourth, it is a pretty well known fact that the conventional air-filling machines do a fairly poor job of removing water vapor from the air going into the tire.

Fifth, and probably most importantly, consider that the nitrogen fill is often done when new tires are installed. So, there is a brand new tire with a clean, slightly sticky bead and a wheel whose rim has probably been cleaned at least a bit, and a new valve...meaning leaks are less likely at the valve or rim. A buddy of mine just had a nitrogen fill on existing tires and they removed every tire, used special sealants on the rim/bead and installed new valves. So...will we attribute less losses to the nitrogen or to the care taken in regard to the rim/bead interface and new, better valves?

There money spent, to the tune of millions and millions of dollars on breast enlargement cremes, penis enlargement pills, copper and magnetic bracelets to "cure" numerous ailments, billions of herbal supplements (that occassionally work, but are always accompanied by disclaimers). The many buyers of this crap often swear by them but, again, it is all anecdote. More often than not, it is a case of mind over matter...and I am all for it because it helps our economy and keeps the fraudsters from perpetrating crimes like armed robbery. But it does not deny that the large proportion of people who are tricked are either not capable of logical reasoning. The want to believe, so they find "proof" that doesn't exist. In short, many are just plain idiots or, at best, foolish. Sorry if that's harsh, but it's usually the truth.

[Hanoch]

I have a 2007 Prius. I have been averaging 45 mpg. I recently had my filled with Nitrogen at my dealer's. Now I drove about 50 miles before doing so and had set the cruise control to 63mph. I got 44.4mpg. After filling the tires with nitrogen, I've gotten 49.3 mpg at the same cruise control setting on the same highway. I know it's not a very scientific study, but I'm wondering if you have tested the mileage with and without nitrogen?

[David Snodgrass]

I always record my fuel and mileage, and have records that go back more than 10 years.
Since buying my 2003 Ford Expedition, I have recorded fuel and mileage when I fill up.
I replaced the OEM Continental Radial tires with Michelin Radials on 01/19/2007.
The Michelins were filled with Nitrogen when Costco installed them.
Costco added Nitrogen when they rotated them.
In 2006 we traveled 9,322 miles and got 13.8 MPG without Nitrogen.
In 2007 we traveled 9,972 miles and got 13.5 MPG with Nitrogen.
Our Expedition is driven in Phoenix Arizona most of the time.
Our driving habits are pretty much the same each year.
I check tire air pressure every three months.
The Nitrogen inflated tires held pressure much better.
If given a choice, I would have my tires inflated with Nitrogen every time.
I would be surprised to see any substantial gain in MPG with Nitrogen.

[Mwb]

This discussion is interesting but I have had a first hand experience that indicates NO net MPG value.

My wife purchase a Hyundai XG350 (new).

The tires have a chronic slow leak. We returned this vechicle many times over a 4 month time period and to no avail.

After much investigation the dealership and a local "Tire Specialist" who checked and replaced the valve stems (twice), checked the rims and their "round", and reconfirmed the tire balance(s) and tire conditions; concluding there was no apparent reason for the leaks. It appeared to be two of the four leaked more but they all had some leakage???

As a final gesture, they filled them with nitrogen.
I checked the pressure and found they were inflated to the max at 45 psi. It took almost 3 weeks but they slowly leaked again to the point where they were noticeably low. Particularily the front two tires?? I did check on the gas mileage and we found that we had no gain or loss of MPG.

I would love to find a MPG improvement in anything right now with the current high gas prices but I can not say that nitrogen is one of them.

Mwb

[Holla]

It shouldn't of made a difference in you mpg, if you have your tires properly inflated all the time.

[carlos]

Lets face it, once you put 30 psi of any gas inside of a tire, the outside does not know what it is inside, it will still behave like it has 30 psi of gas inside. Ok, it is harder for nitro to escape from a tire, check the pressure once a month. Me, I keep mine at 40 psi (from 32 suggested) and get about 3 MPG from the suggested MPG.

[Tommy]

Isn't air already 78% nitrogen? So, just using regular air gives you most of the benefits of nitrogen without any extra cost.

And not having oxygen in your tire may help the inside, but there is still plenty of oxygen on the outside of your tire.

If you've ever taken a tire with dry rot off the rim, you'll notice that the outside looks terrible, while the inside still looks like new. That's because the biggest cause of dry rot is UV rays from the sun. Putting nitrogen in your tires won't help with that either.

Nitrogen is just a way for businesses to take more of peoples money, for very little in return.

[RWS]

Never a believer of the nitrogen in tires, I finally tried it in a tractor trailer. I used to have to replace 4-8 tires a year because of blow-outs especially during the hot summer months. In the last 3 years, not 1 tire lost to blow-out! In over a year, the tires lost only 5-10 lbs of pressure (tires run at 125psi.) whereas with normal air inside of the tires, 5-10 lbs were lost every month. Don't care what anyone else says, I KNOW nitrogen works in tires.

[airairair]

Pathetic! People want to believe that Nitrogen works...so badly...just like the tornado in the air intake gives you more power and increased mpg. What a joke!

[John Scott]

If the 22% of oxygen in an air charge leaks out faster than the 78% nitrogen, then with each charge of air to replace the depleted oxygen, the mixture of gases in the tire casing should become a richer and richer mixture of nitrogen. After a year or so of monthly inflations, you'll have a nearly nitrogen filled tire!

Voila'. Needless to say, I think $20 to fill four tires with nitrogen is just another way to scam money from an ill-informed consumer.

[objective]

Wow, a long and varying set of opinions. I see a lot of comparisons, opinions, alleged scientific data, and anecdotal evidence both for and against the use of Nitrogen in tires. I recently replaced a set of tires with 30,000 miles on them run on "air" with an identical set of tires filled with "nitrogen". I'm in an extremely hot environment. I will report back in 30,000 miles with my unscientific opinions. Based on what I have seen, heard, and some scientific information, it seems like it would be worthwhile, even more so if it was included like at Costco. It also seems, like it might also be very worthwhile on 18 wheelers, who spend a lot of road time in extreme conditions, like heat, and you most commonly see tires blown all over the road. It is not convenient enough presently to be practical for everyday drivers.

[Alienistic]

WHAT A SCAM! Last I remember regular AIR WE BREATHE IS 99.99% NITROGEN! With that thought in mind, are'nt we already filling our tires with nitrogen when we go to the gas station or use our home compressor to fill our tires? How can removing that tiny .009% of non-nitrogen elements from AIR make any difference!? If you really want to save money dont pay $50 to fill your tires with nitrogen, simply check your tire pressure regularly, like once every week or two. If you have a tire thats losing pressure more than the others check if you have a nail in your tire. If there is no puncture problems with the tire then the seal in the valve stem may be worn or bad in which case just stop by your local tire store and have them replace the 50 cent valve stem.

[Kyle Keegan]

There is nothing you can put on your Prius that can get you 3-5 more miles per gallon. That is the stupidest thing i have ever heard. Nitrogen weighs the same and is the same density as air, therefore it is impossible for you to see gas milage improvements.