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

[Ed]

This report does not give a true picture of the advantages of using nitrogen in tires. It is typical of running tests and drawing conclusions under the wrong conditions.
Before I used N, I would fill each tire to factory specs before each long (4000 Miles +) trip, and would invariably have to refill them again after the trip. If I forgot or neglected to do this, the tires wore prematurely on the outside edges due to underinflation brought on by tire pressure loss. This did not happen with my properly filled N tires.

Right now I am still driving on a N refill I got in Olean, NY in the fall of 2006. I have put on 18,000 miles having driven twice to the East Coast, once to the West Coast including two trips to Las Vegas. I reside in Colorado at an altitude of over 6000 ft. where the winter temperatures regularly drop to sub zero temperatures and I drive to altitudes of over 10,000 ft. Not once have I had to add N since this N refill in NY, nor has my pressure varied more than a pound or so through extreme heat and cold conditions. My very sensitive tire pressure system (2006 factory)has remained "silent" throughout all this time, even at 20 degree below zero temperatures.

One other factor the report fails to address properly is that under conditions of driving long and fast under very hot conditions, an air-filled tire's pressure will increase significantly, possibly even approaching dangerous levels. This does not happen with N filled tires. Check out why race cars use N in their tires.

I am not a dealer nor do I operate any kind of tire service. I am retired, and have now experienced at least 10 continuous years of driving with N filled tires. The few bucks spent on getting my tires filled with N is insignificant compared to the extra milage and even tire wear that I have since enjoyed.

[Christopher K]

As a Manager of Vehicle Services for Bridgestone/Firestone, I have had my fair share of questions regarding niotrogen for inflation of tires. As a corporation, BFRC does not condemn nor condone nitrogen for use of inflating their tires. I work in a corporate store, and we do not offer nitrogen as an option to our customers. According to my bosses, the added expense of equipment and increased cost to the consumer versus benefits to the consumer does not warrant the use of nitrogen in tires.

In my 20+ years of automotive experience both as a manager and a technician, I have noticed the average consumer pays little to no attention to their tires until they go flat, or they are worn to the point that the consumer experiences reduced traction due to worn tires.

A tires inflation should be checked monthly, at minimum, according to the RMA. Tire pressure cannot be accurately checked by just looking at a tire. Modern radial tires will have an inherant bulge to them, especially on the front tires, where the majority of the weight is, namely the engine and transmission. the ONLY ACCURATE WAY TO TEST FOR PROPER INFLATION IS TO USE A RELIABLE TIRE PRESSURE GUAGE.

A tire under normal circumstances will lose 1 PSI per month due to permeability. In addition, a tire will gain or lose 1 PSI per 10 degree Farenheit change in temperature. This is why you should check your tires when they are cold. A cold tire is defined as a tire that has not been driven on for more than 1 mile, or one who has sat for 4 hours or more.

According to the RMA, if you must check tires while hot, add 4PSI to the cold inflation pressure without exceeding the maximum pressure on the sidewall of the tire.

If consumers would simply maintain their tires at proper inflation pressure the US could save 4 million gallons of gasoline per day! Unfortunately, the average consumer only checks their tires every 3 months or 3000 miles when they get their oil change.

Please, check your tires, your fuel economy, safety, handling and tire life is at stake!

[Craig j Knarich]

I have just received a call from a good friend about nitrogen and how his buddies are busting on him about the use of nitrogen. First let me state that I have a duel life in the working mans world. I am a state certified engineer in hydraulics in the fire service. I am a professional fire fighter. Second I own by industry standards the most advanced tire company nationwide. PIT CREW TIRE SERVICE I have been in the tire business since 1981. My company was one of the first to go with nitrogen in the states. January 2001 when I built my new truck I thoroughly researched the gas and reviewed its results in Europe. It had been used in Europe since the 1990's the difference is I wanted to do my own study so I invested in a $10k industrial grade nitrogen generator.(AIR PRODUCTS) I used it for 2 years without telling my customers what I had done never charging them a single dime. My blind study showed that my customers enjoyed the ride of there car better and they started wondering why the tires lasted longer and had improved gas mileage for those freaks that really watch there fuel economy. And yes I had a few. How do I know this, I call every customer after I put tires on there cars. Yes not the norm but I can tell you first hand it works. My company does not charge for nitrogen you purchase tires I give it free. It is a cost of doing business. I will tell you I would never pay for nitrogen in my tires I have seen what the bean counters are doing and it is going to bite them right in the BUTT. nitrogen generators must be serviced once a year. They must have the prism membranes and the o2 sensor changed at a cost of around $500 annually and they are not doing it. Plain and simple nitrogen is like bottled water was in the 80's want to buy some bottled water and the laughed you out as they went to the tap. Now nobody drinks tap water that is why I don't sell it but be warned there are people out there that are unknowing selling air at nitrogen prices and I have seen it first hand. Warning if you buy it ask them to show you a o2 gauge to prove that they are adding n2 as long as your tire obtains a 95% or better concentration or the o2 sensor gauge reads 4.0 or better you are o.k. Air is 78% nitrogen 21% oxygen and 1% other gasses. NEWS FLASH they tell you the reason oxygen seeps through the betel sidewall because the oxygen is smaller and the n2 molecule is larger that is false and every reporter gets it wrong along with the sales men n2 is smaller o2 is larger the n2 molecule is very dense and the o2 molecule is not that is why it seeps through and that is why you get a better ride and improved mileage. The tire also will stand taller and be more rigid and have reduced tire squirm and hydro planing in rain Second the people in southern states will benefit the most and will notice the difference more. The only people that will not notice a difference are those people that are driving on run flat tires there are many more thing I could debate about this but there is only so much time I will tell you yes it works and the tire dealers should give it for free when you purchase tires from there store.

[HAROLD HERZLICH]

Nitrogen inflation of tires is the next paradigm shift in tire maintenance. Rubber oxidizes and the expensive antioxidant chemicals incorporated during manufacture, while being effective, are consumed or lost during tire service. The opportunity to inflate with an already proven oxygen free, less permiable inert gas that helps the tire retain it's pressure longer while virtually eliminating the inflation oxidation component is something the industry should encourage rather than taking a neutral position.

Under inflation is a major contributor to tire over heating, injury, vehicle loss of steering control, loss of wet traction and tire failure.

TPM devices are not going to eliminate marginal under inflation misuse. In fact these devices may encourage it by having the motorist believe that tires don't have to be checked until the device triggers (at 20% underinflation) when it's already weakened the tire and caused an increase in fuel consumption.

While one psi advantage may seem small, fuel consumption increases by about .33 percent/psi.

Rather than the micro effect on an induvidual, environmentally responsible CR reporting should include the macro carbon footprint benefit of nitrogen inflation for the billion tires that are delivering 3 trillion miles of service per year.

Environmentally responsible people know the single aluminum can they recycle, will by itself have no measurable benefit, but when the macro effect of milions of people acting together, the benefit is massive.

Your readers are smart enough to crunch the numbers and be amazed by how much fuel is saved by an even small improved nitrogen inflation pressure advantage.

TPM devices will benefit from high purity nitrogen inflation with fewer false alarms,less marginal untriggered under inflation and other damage.

Nitrogen inflation will improve a vehicles fuel performance. it will not make a tire bullet proof. Some claims being made are not technically sound and are actually irresponsible, hurting the concept.

CR should amend it's report and extrapolate its inflation differential findings to fuel efficiency on a billion tire/three trillion miles per year macro scale showing the many millions of gallons of fuel saved. It is reported that under inflation wastes an estimated 600 million gallons ($1,800,000,000 at $3.00/gallon) per year. How can we conclude that nitrogen inflation is too expensive???

Why doesn"t the Department of Energy get involved?

[Greg]

Another recent CR article states: "What’s more, all tires tend to leak over time. Pressure loss averaged 6 psi for 36 all-season models we checked after one year." It is located at: http://www.consumerreports.org/cro/cars/tire-maintenance-1205/index.htm

How does that study differ from this study? Why almost double the difference (3.5 lb to 6 lb) in air pressure loss?

[Joseph Ruan]

Your getting ripped off and thinking your getting better gas milage is your imagination. I worked as a tow truck operator 15years and have been a tire manager for the last 8years and the air you breath is 75% (3/4) nitro. Joe the Tire Guy.

[DJlargo]

Air is already 80% nitrogen. And its free. If you want to pay for 95% nitrogen be my guest.

[EWordmon]

Darn! DJlargo and Joe the Tire Guy beat me to the punch. This ought to be on Penn & Teller's show.

Air is already 80% nitrogen. Hey, but if you want to pay $20 for 95% nitrogen by all means...

Most likely the gas mileage improvement is due to slower pressure loss over time. Harold hits the slower pressure loss above. The savings are negligible.

Go for the low hanging fruit. Make sure you change your oil. Use a lower viscosity oil if your owner's manual indicates you can. Make sure your air filter is clean and changed often. Ensure that your car has had a recent tune up. Check belts and/or serpentine belt.

And most important, check your tire pressures often. This will negate any comparison with air and 95% nitrogen and is a good practice anyway... ;-)

[Keane]

For the most part, if you are driving a normal car and not for racing, I would think that air is good enough considering the fact that it already has 78% nitrogen.

The key is to check the tire pressure regularly, at least once a month for vehicles and once a week for motorcycles.

~100% nitrogen filled tires can only help that much, it still depends on you to be discipline enough to check the tire pressure on a regular basis.

[TangoCharlie]

Reality check on nitrogen.

1. "Believe Ideal Gas Law. It simply states that N2 and "air" are pretty much the same thing, so both will act the same."
Fact: Incorrect. Fact is that Oxygen in the air permeates (leaks) out FOUR times faster than nitrogen. That makes nitrogen retain tire pressure for longer time.

2. Nitrogen "Drivers should check and refill tires regularly - monthly, if not weekly."
Fact: Most of us DO NOT check tire pressures regularly. At most, it is visual inspection, which can be very inaccurate. For many people, refilling tires less often with nitrogen is a convenience which may be worth $20.

2. "Air is already 78% nitrogen, what good will it be to get >95% nitrogen"
Fact: It is the OXYGEN that is bad. Oxygen leaks out of tire 4 times faster than nitrogen and also contributes to rubber damage. That is why bags of potato chips are filled with nitrogen - to preserve it. With nitrogen tire filling, bad oxygen is reduced by >75%.

3. "Industry spent millions of dollars on TPM systems. They will warn of low tire pressure anyway"
Fact: TPMS will light up only when pressure goes below 25% of set pressure. That is 8 psi in a 32 psig tire. At that point, cars will have lost >5% extra in fuel besides having measurable negative safety impact.

4. "Savings with nitrogen are miniscule and economically unattractive to consumers"
Fact: If ~3% (10c/gallon) are minisule for average driver, yes, the savings are miniscule. Regarding individual payback, you may also consider not buying energy saving devices like CFL light bulbs, more expensive energy saving appliances and hybrid cars because they all have multi-year payback.

[Tom]

Take it from an engineer. One common claim made by tire dealers is that nitrogen-filled tires do not react as much to temperature as air-filled. This claim is false! All gases change volume essentially the same amount due to temperature changes. (read a thermodynamics textbook) The difference between air and nitrogen is so small you could never measure it with a tire guage. So remember to always check your tires because even if tires didn't leak at all seasonal temperature changes will affect tire pressure enough to make a significant difference.

[Steve S]

I'm going to address just one point - the effects of the differences in leak rates for oxygen and nitrogen through a tire. Assume that the leak rate of nitrogen is one-forth that of oxygen, as some posters have claimed. Further, take the example of a tire that, when inflated with air, loses 5 psi per month. Since the leak rate of oxygen is much faster than nitrogen, and since the tire is filled with air which is approximately 20% oxygen (that is, contains 4 times as much nitrogen as oxygen), the tire in it's first month will lose equal amounts of nitrogen and oxygen.

Then, the tire is brought back up to the correct pressure using plain ol' air. But now, the tire contains more than 80% nitrogen because the added air was mostly (80%) nitrogen.

The effect of this, over several months, is to gradually increase the percentage of nitrogen in a tire. In this example, the tire reaches 90% nitrogen in 4 months, and it stabilizes at about 94% nitrogen after 12 months.

Hence, in this example, you get much of the (supposed) benefits of nitrogen just by the normal process of keeping your tires topped off at the correct pressure.

The percent nitrogen in the air that the tires stabilizes at is the same, and is only dependent on the relative leak rates of oxygen and nitrogen. The time (number of months) that it takes the tire to reach this point is dependent on the absolute leak rate through the tire. The slower the leak rate (for both oxygen and nitrogen), the longer to reach the equilibrium point.

[pmk]

Let me start by saying that I've been a tire engineer for 15 years.

No tire company inflates their tires with N2. It's been tested, it's a joke. Rolling tires don't lose more air through the innerliner than tires sitting against a wall. If anything, they may lose air due to tires slipping on the rim during accel/decel, but that would further squelch the differences seen in the CR study. Save your money for a good gauge and use it often.

[Robert Kershaw]

It seems there is a lot of discussion on the benefits, or lack thereof, when using nitrogen for tire inflations. No one has mentioned the hazard of using pure nitrogen.

For a homeowner with a nitrogen generator in an open garage, the danger is probably very low. But, if a tire shop replaced the air compressor with a nitrogen compressor the breathing hazard could be very real. Humans require a minimum of 10% oxygen to remain conscious. Less than 5% oxygen is usually fatal. Using pure nitrogen in a tire repair area where inflation, breakdown, re-inflation occurs could result in death.

The petrochemical industry has used nitrogen for decades and has developed very strict rules for handling, connecting and working around nitrogen. BREATHING PURE NITROGEN IS FATAL.

If you use nitrogen please consider the hazard. Never inhale pure nitrogen. Ensure adequate ventilation is present. Place appropriate warning placards around the nitrogen generator/compressor or use area.

[Chris Fogerty]

Some are saying they get better gas mileage with the nitrogen in their tires. Did they have proper pressure before you changed to nitrogen???

[Darrell]

Nitrogen, intake 'turbinators', fuel system 'rare earth' magnets, fuel 'catalysts', oil additives, pricey 'high power'/ultra low resistance spark plug wires, spark plugs with split electrodes, etc all have one thing in common. The separate fools from their money make and con artists rich. Properly maintained vehicles that use high quality fuels and fluids will not benefit from any of these modern snake oils. But if it makes you feel better, then go for it.

Added note re nitrogen and prevention of rubber deterioration not mentioned in previous posts: The most significant rubber deterioration occurs on the outside of the tire where ozone and UV light from the sun are the major agents causing damage. Take a look at the inside of a 5 year old tire freshly removed from a wheel and note the the rubber is smooth and looks new. Now look at the external side wall. Put another way, tires rot from the outside in. Nitrogen inside the tires will not prevent this external damage.

[David Smith]

I vote for nitrogen. I have a Convaid stroller for my daughter. The Convaid is like a wheelchair. The 8" front tires are quite small, and carry a lot of weight. I had to pump them up quite regulary. Then I found out the local Costco inflated their tires with nitrogen. They graciously pumped up the tires of the stroller. I noticed that the tires maintain their pressure longer, and I have to pump them up only about 1/4 as often. I didn't do a scientific study/keep track of dates and pressures, but my experience is enough to convince me that filling tires with nitrogen has merit.

[David Smith]

A suggestion for CR in a follow-up study: repeat the study with pressure monitors on the tires. Log the pressures as vehicles drive in different conditions and report the results. CR could also look at other factors such as road surface quality, style of driving etc. Putting air and nitrogen tires on the same test vehicle would eliminate many independnt variables.

[Beejal]

I have a pair of Goodyear Allegra passenger type tires that benefited quite a bit from inflation with nitrogen vs. air. When I inflated them with air, they seemed really susceptible to pressure fluctuations (both up and down) when I checked them 1-2 times per month. Also, the ride was very uncomfortable (hard and noisy) and the handling was loose compared to the OEM Bridgestones on my Mitsubishi Galant.

I was very disappointed with my tires, but after hearing about nitrogen inflation, I decided to give that a go. After inflating the Goodyear passenger type tires with nitrogen, my ride is much quieter and more forgiving over the rough roads here. The handling did indeed "tighten up." Finally, the pressure fluctuations stopped... I still check the pressure in my tires monthly, and over the course of 14 months, I've only had to adjust the pressure in my tires once (vs. 5-6 times with air-filling).

My fuel economy is the same since I previously monitored and adjusted the pressure in my tires frequently. However, I still feel like the nitrogen is a worthwhile investment, as it also improved ride and handling for me. I think the relative lack of water vapor in nitrogen vs. compressed air is another reason for the advantages.

[Travis]

As a mechanic I think the two biggest problems with nitrogen (other then it being a scam) are.

You normally can't get it at a smaller garage or quick lube, so you have to go to a tire dealer every time your tire is low.

And the bigger problem is no one ever checks thier own tires. They expect someone else to do it. And if they are bringing it to a shop without nitrogen they probably aren't doing it either. Not just because they don't have nitrogen but, because the last time someone with nitrogen filled tires caught them checking thier tires they got yelled at. So after one or two oil changes of not checking the tires the ones with nitrogen will be under inflated and the ones with normal air will be right where they are supposed to be.

I don't know how they are marketing this stuff but, you would think that any body who paid extra to have more constant tire preasure with 95% nitrogen would be willing to let it get dilluted down to 94% or 93% so that they are actually at the proper PSI.

[John Palazzini, Woodland Hills CA]

I would also think that there would be alot less oxidation with a nitrogen filled tire. Neoprene oxidizes over time and will have its physical properties compromised. So, with Nitrogen, there should be less oxidation and hence, less degradation.

[Mike Demers]

A few missing bits of information. The temperature/pressure factor is influenced by the amount of water vapor in the tire. The water vapor is the reason for pressure differences with temperature changes. The required 95% purity of N2 in the tire assures that most of the water vapor has been removed. A static test of tires is not a true test, a tire in use on a vehicle goes through many temperature changes, which changes pressure. The higher pressure from high temperatures should cause more laekage. Tires inflated with N2 are not as susetable to huge pressure increases/decreases caused by temperature. Remember--even 1% underinflation will decrease fuel mileage and tire life. The new Nissian GTR is reported as having N2 in the tires from the factory.
Key ingredients for proper tire inflation: 95% purity and monthly pressure checks.

[Doug]

First of all, it is not Nitro, it is Nitrogen, they are completely different topics.

The amount of difference Nitrogen has made in my 99 BMW M3 is, absolutely nothng, but then again, I monitor tire pressure very regularly, just like my oil level & everything else about the car or the SUV I drive sometimes, or any vehicle I've ever owned. Everyone should.

I monitor tire pressures, and I use my car for driving to work, at High Speed Driving Events, and at a race track for the occasional track day. I have thoroughly tested the difference between running Nitrogen & plain old air on the track & on the street & guess what? There is no difference after trying it in multiple setes of tires, none, nada... None of my tires wore out from the inside out, so Nitrogen didn't help that, & wont help you either, if you keep your tires on for 10 years, the rubber has lost it's effectiveness anyway, so Nitrogen isn't going to help there.

I hope none of you would go without checking tire pressure for months at a time, and if you do, why bother with Nitrogen, when you obviously don't care about safety, mileage or tire wear?

People who buy Nitrogen, dont' even get me going on the environmental issue, change your oil & all your filters, check your tires, & keep your car tuned up, or stay quiet about the environmental impact, unless you ride a bike all the time.

The science behind Nitrogen sounds good to most people, but in practice, the first time you add air, (contrary to what the confused Steve S is talking about above???), you increase the ratio of O2 in the tire slightly, and eventually, the tire becomes the same mix as the outside air.

Go ahead, buy Nitrogen from the snake oil salesmen, while you're at it, buy a Q-Ray bracelet. Oh what's that? You already have one & it makes your life better? Brilliant. Spend the money on a tire gauge instead dammit & use it more often.

[Joe]

CR only bothered to look into one of the benefits of running nitrogen in tires. They did nothing to determine if tires run cooler when filled with nitrogen rather than air and they did not look into any issues regarding nitrogen being more "friendly" to the rubber. CR kind of dropped the ball on this one.

[tim hughes]

I tried an experiment using nitrogen in the rear tires of my corvette and air in the front. Although I could not tell any difference in grip, I have replaced the rear tires twice while the front are still in good shape. I agree that after using nitrogen on 2 different occations in the rear tires, they indeed wore out quicker with no difference in grip,braking or traction.