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

[Alan Ollie Gelfand]

The bottom line on what to put in your tires. Free Nitrogen or clean dry compressed air. Automotive shops need to have clean compressed air. At my shop vdepot we have air line dryers and filters that take out oil and moisture. Keep your tires at maximum recommended pressure with clean dry air and check pressures often. Alan Ollie Gelfand owner VDEPOT

[AOA]

DOT Research report to Congress on Tire Aging said: The loss of inflation pressure between room controled and real world use of tires could be up to 20 time greater. This test was to examine the effects of heat built up, on the relationship between the amount of oxygen permeating through the tire and the rate of thermo-oxidative degradation. In the same report Exxon used nitrogen inflation and tests showed that nitrogen can reduce the static air loss rate by 45% and correspondingly reduce the rate of aging. CR please post real world test. With so many tire failures that lead to accidents and loss of life why is this an issue.

[SCOTT M.]

I`ve been a A.S.E. certified master tech since 1992 and have owned my own shop for 7 years.I`ve read a lot of articles and studies on the subject.The bottom line is that the whole nitrogen "thing" is a gimmick!The equpiment companies want us(repair shops)to buy a $7500.00 nitrogen filling station(that lasts for about 5-8 years).The tire salesmen work off of comission in the big tire shops.You do the math.At $5.00 a tire extra and selling 20-30 tires a day????Hmmmm,I wonder?
As stated by others,Earths atmosphere is 78.8% nitrogen.Can the other 15% make THAT much difference?-No! Common sense goes a long way and your test proves it.There are a lot of variables and you can run hundreds of tests,different tires,wheels,temperatures,vehicles of different weight,etc....Every test may have a different result.
Once again as stated by others..why do you think the manufacturers spent millions of dollars on tire pressure monitoring systems.People are generally too lazy to check the tire pressure.After the Ford Explorer/Firestone fiasco do you think they(Ford,GM,Toyota,ect.) really want that kind of problem again????? Every day the customers go to the dealers and complain that their 80,000 mile Michelins only got 65,000 miles and the want their money back!!!!Check your tires on a regular basis and rotate them every 7500 miles.Regular maintenance goes a long way and common sense goes even further.
Anyone that thinks putting nitrogen in your tires will give you 3-5 miles a gallon better is the same foolish,gullable person that thinks buying a Prius is/was good idea!!!!You should have saved your money and bought a used Geo Metro or an old VW Rabbit diesel!!!!!!!

[Dodger]

Since most of us do not let our cars sit for one year unused, the test is invalid. If, using new tires, CR inflated with nitrogen one tire out of four on a test automobile or pick-up, drove the vehicle for a year, then compared the tire pressure and tread wear, then the test would have relevance. I doubt any of us let our car sit unused for a year. Besides, the CR test tire did not have any weight on the tire. I think the test was meaningless.

If you are going to test something, then please do a valid test.

[dominick]

I noticed one comment that brought up the fact that tire pressure goes up or down with each change in temperature. It is about 1psi for each 10 degrees of change. If you lived in the upper midwest, and filled your tires to the best pressure during the summer, they could be up to 10 psi underinflated in the dead of winter, or vice versa. In fact, you might even notice this difference if you checked the tire pressure between the side of your car exposed to hot sun for a few hours, and the side sitting in the shade. Therefore, if you live in a climate with wide swings in temperature, using nitrogen doen't seem to make any economic sense for the minor improvement in loss of pressure.

[Ricko]

There used to be a joke in the auto repair business about asking the customer if they would like to change the air in their tires..........Now it's happening!

[Mike Robinson]

I have had my tires filled with nitrogen and have noticed a better smoother ride and I have increased my mileage by 20 miles more per tank, that is proof enough for me since I drive 26 miles one way to work

[Robert Tucci]

It is time for a chemist to weigh in here! Air is mostly nitrogen it is true. And the oxygen in air will have some very limited negative effect on rubber which will increase exponentially with heat. However, the real reason that nitrogen works is because the nitrogen enriching equipment also desiccates the air in the course of enriching to 95% nitrogen. It is the humidity in ambient air which cause many issues.

Have you ever noticed liquid water coming out of the air hose used to inflate your tires? Humid air will drop out liquid water upon compression (service station air) or cooling (evening dew on the lawn?). Liquid water will vaporize on expansion (as you fill your tires) or with heat (as you drive down the highway).

We are told to inflate cold. We add water vapor and sometimes liquid water. Then we heat our tires and the water expands, increasing our tire pressure. Tires loose pressure more quickly at higher temperatures. Our tires then have less pressure upon cooling. Dessicated air expands more consistently (following the ideal gas laws). Water is not an ideal gas!

So, net net, nitrogen doesn't help or hurt. Dessication helps. The nitrogen guys selling the equipment know this is a major benefit, but dessication is much cheaper.

[Jean Eastin]

As a driver of over 44 years I got a 2007 Toyota two years ago and have had nothing but trouble with the Bridgstone nitrogen filled tires. I think in 44 years of driving I have only had 3 flat tires. I have 5 blow outs or gotten screws or nails in them. Two of the tires had the treads worn with less than 20,000 miles on them. I hate them..........When the weather turns cold the tire light comes on....I go around and check the tires and they have 32 lbs of pressure..... I live in Fl. and after a cold spell of 3 days last year and 2 days this year the pressure light finlly goes off. I have called my dealer and another dealer and they all tell me nothing to worry about it's just the cold weather. They (service managers)both said they have had over 100 calls. wonder what is happening with the cold weather up north. I am no chemist...but something is going on with the nitrogen and giving a false setting. I am wondering if it somehthing with the nitrogen. I have owned a brand new car for less than 2 years and I am on tire 5. It is disgusting, not only could I have been killed a couple of times the time and energy lost for the replacement of these $252.00 tires. I wonder if any one out there has had any troubles like this?????

[Robert Cornforth]

I bought a new GMC Acadia on Sep 5, 2008 with nitrogen filled tires. My wife and I took a trip from Pheonix, AZ to the Washington DC area at the end of September, and before I got to my destination in VA, I was already getting a message on the instrument panel to check my tire pressures. They had dropped from the delivery pressure of 35 PSI to 28 and 29 PSI. The new vehicle now has 6000 miles on it, and the tire low message appears every time I start the engine. The closest place to get them refilled with nitrogen, is at the dealers where I bought it inScottsdale, AZ, about 15 miles away.

[cartboy]

Enough with the nitrogen bull. This all started when someone noticed tanks in one of the pits at a nascar race and asked what they were and what for. Air from a compressor has a higher water vapor content than nitrogen and since nascar adjusts tire pressures as little as a 1/2 pound it is easier and more accurate to work with the nitrogen.Remember to drain the water out of your compressor after you shut it off.

[Ken Perkins]

If there is nothing to it how come they use nitrogen in the tires on air craft and NASCAR.

[Richard Greifer]

Just purchased an Audi TT which came with nitrogen filled tires at no extra charge. My dealer said he would top off the tires with nitrogen at service time or whenever needed for free. The dealer also said tires would hold nitrogen for 6 months before needing a top off or get a top off sooner if the low tire pressure warning light goes on. On my previous TT's(without nitrogen), I checked my air pressure once a month and typically needed to add 1-3 lbs. of air. I believe nitrogen leak is less than that of a tire with air for maybe a couple of months, however, after that, until six months comes around, I'm convinced thatI would be driving around with underinflated tires, thus introducing added wear an a poorer ride. In summary, I'll check my pressure once a month and refill with air. That way I'll know I'm driving with properly inflated tires. I believe the industrial gas industry is using nitrogen in tires as a ploy to increase revenue. Any benefit of nitrogen is negated by driving with underinflated tires. As the saying goes, the cure(nitrogen) is worse than the disease(underinflated tires).

[Nate Hager]

unbelievable, CR does an article and then many comments are made without one mention of the TPMS systems in modern vehicles. The feds mandated that a TPMS (tire pressure monitoring system) shall be in all new vehicles sold in the U.S after sometime in 2007. The TPMS system is designed to ensure proper tire inflation even for those people who are too lazy (or don't know how) to check their tire pressure. The system utilizes sensors that are in each wheel to maintain proper inflation, warning the driver of a pressure change usually greater than 3 psi. Well let me tell you it works! I live in Colorado at high altitude and drive down to a lower elevation to go to work. The TPMS system works so well that it would come on nearly every day (due to the elevation changes, and the temperature difference). So when this light comes on in the dashboard the driver is left with a question: Does one or more of my tires have a real pressure problem? ie:picked up a nail, or is my TPMS system just doing it's job? well the natural reaction is to eventually ignore the TPMS system.
Now I am not saying the Feds are always right (rarely in my opinion) but I think they hit the nail on the head with the TPMS system. The mandate was made as a solution to the Bridgstone tire/ Ford Explorer problem. A federal study found that the tires were good tires, as long as they were properly inflated. When they were under/over inflated was when the problems occured. So they recommended TPMS systems to solve the problem. The thing they left out is nitrogen to go along with that system. I put nitrogen in my tires and have not seen a TPMS light in a little over a year, and guess what, the pressure remains the same in that same amount of time! Also consider the fact that air filled tires contain moisture (undisputable) and the combonation of moisture and oxygen is detrimental to the TPMS sensors, which cost around $100 each!! The sensors will last longer in the dry, oxygen free environment of a nitrogen filled tire. The benefits of nitrogen are far greater than have been discussed here!

[Bill]

As a retired airline technician may I say that airline tires which go from extreme low temps in high altitude to hot landing temps in hot areas perform extremely well for the reason they use nitrogen. The variations of actual tire temp is kept to a minimum. This increases tire wear and performance. Wear is relative as the landings wear off a great deal on touchdowns. If you purchasem tires from Costco they install nitrogen free of charge and you can have them check your tire pressures for free and they will adjust up if neccessary. Nitrogen is better.

[B Davis]

Another point to remember is that normal compressed air is wet, Nitrogen systems are dry. The lack of moisture decreases the rust on the rim and any metal belts in the tire. It also maintains a more even temperature while traveling as the water in the tire is not freezing or expanding

[al]

I tried nitrogen in only 2 tires and found no difference.
I recommend that you don't pay extra for nitrogen

[Brad Holt]

Perhaps we should inflate our tires with helium, so they would be lighter, which should improve gas mileage.

[Richard]

Since atmospheric air is 78% Nitrogen, and since air leaks out of tires faster than Nitrogen according to your tests,doesn't that mean that of the air filled tire the Nitrogen component is leaking out more slowly? Shouldn't the level of Nitrogen in an air filled tire increase and approach 100% after multiple refills?

[Craig Weuve]

Nitrogen can and will help do a lot of things but has of Aug 31, 2007 all vehicles below 10,000 ponds have a Tire Pressure Monitor system (TPMS). The nitrogen is dry where the air we get is often contiminated whith impurites and water this will effect the way TPMS works, and the systems are very expensive. So if you have dry air and uncontiminated go a head and use air but I would use nitogen for these systems

[Shlomo from Carterville]

People seem to miss the point. Nitrogen is a "SAFETY" feature. It minimizes the need to 'check' tire pressure. For the same reason "idiot" lights were added to cars instead of oil pressure guages, etc. Nitrogen may "preserve" the integrity of tire construction for a longer period of time. Nitrogen is a "preventive" solution for people who take the path of least resistance/maintenance.

Think about the 75-90 percent of Americans who keep their cars outdoors, live in metro areas, hardly ever completely dig out from snowstorms, etc. If it prolongs tire life with regard to treadwear and/or mileage (mpg)---great!!! But, Nitrogen is more importantly, the safety feature for tires for the great mass of people who park outdoors in urban areas, for whom finding a 'nearby' station with air is not a snap, as well as for all of us "idiot" light people.

[Steve Grant]

You did not use a "real time" test. A tire that sits outside after being inflated with both nitrogen and air as a comparison omits the heating and cooling cycles and sidewall flexing that occurs when tire are used in the real world. Try it again before you endorse or condemn the nitrogen thing.

[Dave Windsor]

I refuse to buy into the nitrogen hype as the hassle and additional cost are not worth it. What I have done is filled my tires with helium. Yes.. I know it's expensive but my tires are SO much lighter now my Prius is getting astounding mileage. I just find it a bit inconvenient to drive to Party City to fill up my tires when the pressure is low. I also find it disconcerting on a windy day when my Prius nearly floated to the next lane!!

[tom salisburg]

Air supports life. Many people have been killed using 'inert' nitrogen unsafely. Maybe not a big risk in this application, but walking into a confined space (e.g. garage) where nitrogen has leaked has taken many lives. Remember you can't tell that you are gradually being asphyxiated -you just loose consciosness as do the people who come and rescue you who also can't detect anything either you. The science for automobile users supports marginal at best improvements -if you want to save gas moderate your driving style.

[Mikey]

Sounds like a great way for auto shops to make more money off the gullible. The changes observed by Nitrogen users are likely caused by the placebo effect -- people experiencing and observing data that supports what they want to see. There are a lot of reasons any improvement (other than the potential reduction of pressure reduction) would be unlikely. For you thermodynamics geeks, the differences in Cp (or is is Cv?) of air vs. nitrogen are miniscule. Good job, tire marketing guys... you're making more money off the foolish. What did PT Barnum say? LOL