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

[Peter Vongboupha]

Were the tires installed on a vehicle? Would the weight of a vehicle have a greater effect on the loss of psi?

[Howard]

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.

[William A. Tomb]

Were the tires on new rims or older ones?

[Brad]

I think the bottom-line comment about being sure to check pressure regardless of air or nitro is key. I think the tendency would be to NOT check nitro filled tires as frequently as air filled.

[Janet Givens]

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.

[Tuan]

I agree with all of the comments above. It is a best practice to regularly maintain a car. Many people will get the oil change and for the most part, it ends there. Skipping scheduled maintenance may save money in the near term, but the long term wear on a car that is not serviced can lead to much more expensive remedies.

Car tires should be visually inspected before one drives their car.

[Kyle]

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.

[Chris]

Good Point!!!I hadn't looked at it that way, Think I'll skip the Nitrogen

[John]

I just had Nitrogen added in our 99 9-3. I'm getting roughly 1 mpg better than before. I also noticed a difference in the ride. It seems there is less give and therefore thighter steering. My wife who didnt' know about the nitrogen made the same observation about the handling. Anyway, seems worth it to me.

[Jason]

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?

[mark]

I agree with the other post that the test is flawed because it leaves doubts in people's mind, what if the tires got actually mounted to the car and driven around as they should be. Will the results be the same?

On the other hand, air contains 80 % of nitrogen already, and we are paying $5 a pop to increase that to 95%? Why?

[Norman]

I use ordinary air in my Prius, but spent $40 on nitrogen for my wife's 2007 Camry hybrid. Within a few months she flattened two tires on road trash and destroyed a third while trying to evade a pothole. My 2004 Prius, which has never had a flat, surpasses without nitrogen the mileage of other Priuses I have checked. Is there a message here? I suggest that driving technique may do more for fuel economy than nitrogen.

[David]

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 intert 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 overinflation and wear/tear resulting from heat build-up.

[Brad]

This seems like a flawed test because the tires weren't tested under "normal operating conditions." CR wouldn't test mattresses for excessive sag just by leaving them in the lab for a year or evaluate a car's gas mileage by running it on a treadmill. Ride comfort, tire handling and tread life and even braking distance could all be different for air- vs. nitrogen-filled tires. This "research" is irresponsibly shallow.

[Patrick]

May I suggest that improvements seen in MPG and ride comfort by using nitrogen are a result of the placebo effect? If you get N for "free", such as at Costco, then fine, enjoy your green valve caps, but paying money for the stuff is like throwing it into the 80% nitrogen wind!

[WIlliam Stackhouse]

What about daily, weekly, and/or monthly fluctuations due to significant changes in the ambient air temperatures? While PSI LOSS (from Oct to Oct when ambient air temperatures would be expected to be consistent) was comparable between Air and Nitrogen filled tires, would you expect that the PSI VARIATION due to ambient air temperature changes over shorter periods of time could be much more pronounced? Also, the question that was posted by someone else about the heat build-up during sustained highway driving is a related question that should be answered.

[Steve Sasaki]

If you don't want to give any credence to this test that's fine. Enjoy your proven increased mpg, handling, and "ride comfort" (See anecdotal evidence). But there are physical laws that we abide by here on earth and one of them is called the Ideal Gas Law. It simple states that N2 and "air" are pretty much the same thing and that they both share the same characteristics in a tire such as thermal expansion, molecule size, etc. CO2 also falls under this law. I don't know if I'm going to start hearing many bubbles bursting but if you don't want to believe me then believe the tire companies. They do have some smart people working there. I assume one day green valve caps will be a sign of ones gullibility.

As far the corrosiveness of O2 in air. You do have a point there. Luckily, tires wear out years before the effects of O2 would ever show any signs. There are other factors way more damaging to tires than air: UV, road hazards, poor maintenance, dog pee, the curb, my wife...

[Chris M]

The respondents that stated better fuel economy, must not have had proper inflation to begin with. PSI is PSI. 95% Nitrogen or air. As long as the PSI is the same, fuel economy would be the same. 95% Nitrogen would be lighter than air but it would not be enough to make a difference in fuel economy as long as PSI is the same.

[Steve Motta]

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 100psi.

Please consider a second, more complete look at this.

[Chris M]

The respondents that stated better fuel economy, must not have had proper inflation to begin with. PSI is PSI. 95% Nitrogen or air. As long as the PSI is the same, fuel economy would be the same. 95% Nitrogen would be lighter than air but it would not be enough to make a difference in fuel economy as long as PSI is the same.

[Darren Stukes]

If nitrogen is free sure why not. If I was planning to reuse the carcases of my old tires as they do commonly in the Heavy Duty industry- lets talk. This should not even be an issue if your 3,000 mile interval oil changes include checking your tires- if not I would look elsewhere for service. Other than that- Buy yourself $2 air gauge and check your tires when you get gas. Nitrogen doesn't prevent flat tires- and the last time I checked 1 PSI didn't make the difference when the guy next to me on the freeway had a blowout from a FLAT tire he was driving on.

[Jeff Bartlett]

There has been great interesting 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.

Click on my name below to visit the post, also at:
http://blogs.consumerreports.org/cars/2007/10/nitrogen-tires-.html

[David Scribner]

We have seen a study by a major vehicle manufacturer which revealed most air pressure loss in tires does not take place through the sidewall of the tire but is due to tire bead to rim bead seat and flange leakage around the valve stem and valve core areas. I dont think any type of gas used would improve pressure loss in these cases.

The Rubber Manufacturers Association has also issued this statement:

Applications such as aircraft, mining, and commercial/heavy use utilize nitrogen to help reduce the risk of internal combustion (fire) if the brake/rim/wheel components overheat. Also, dry nitrogen is used in professional racing to help reduce variation in inflation pressures (caused by moisture) where even small differences in pressure can affect vehicle handling at the extreme limits of performance.

For normal tire service applications, nitrogen inflation is not required. However, nitrogen inflation is permissible as its properties may contribute to minor reductions in inflation pressure loss. Nevertheless, several other sources of pressure leaks, such as punctures, tire/rim interface (bead), valve, valve/rim interface, and the wheel, may negate the benefit of nitrogen.

If the tire inflation pressure is below the pressure specified on the vehicle placard, the tire must be re-inflated – whether with air or nitrogen – to the proper inflation pressure.

RMA warns that depending on nitrogen alone to reduce the requirements for inflation maintenance may, in fact, lead to under inflated operation, which may result in premature tire failure.

“With the right amount of inflation pressure, you will achieve optimum tire performance,” RMA wrote. “This means your tires will wear longer, save fuel and help prevent accidents.”

And above all, the RMA bulletin strongly reminded motorists to check tire pressure at least once a month when tires are cold and to use the vehicle manufacturer’s recommended inflation pressure.

“Whether inflated by air or nitrogen, regular inflation pressure maintenance remains critical and necessary,” RMA wrote. “Use of nitrogen alone is not a replacement for regular inflation pressure maintenance.”

The RMA bulletin notes that nitrogen is an inert (non-flammable) gas – basically, nothing more than dry air with oxygen removed (air contains about 78% nitrogen). Because of its inert properties, nitrogen is often used in highly specialized service applications and/or demanding environments.

[Note - CR shortened this message for space, though did not alter content.]

[Frank Ruscitti]

My question to Consumer Reports

When filling the Air Inflated Tires was the air source using a Refrigerated Air Dryer or some type of Moisture Dryer?

Most comsumers fill there tires with Compressed Air that has not been filtered and I personally have seen my wifes Volvo lose 2+ Pounds per month and have upto 10 PSI Pressure increase on a hot day in AZ.

With Nitrogen I see almost No Pressure lose with Monthly checks and only a 4 PSI Increase.

This gives the vehicle a very much improved ride and handling.

I paid $29.95 for the inflation and feel that If I receive only a 10% better tire life that pays for the Nitrogen.

The ride and handing improvement is more then worth the cost.

[Mat]

As many have already pointed out, this report is flawed in that it is not reflective of actual real life conditions where tires under continual driving conditions lose pressure much faster. As a long time subscriber to CR, I am disappointed by the incorrect inference it may lead to. But, as the report’s bottom line points out there is no substitute for checking tire pressure regularly.

Four point to make:

1. Various studies point to higher average pressure loss (about 1-2 psi per month). One Bridgestone study says air inflated tires lost an average of 2.7 psi per month and nitrogen inflated tires lost an average of 0.7 psi per month. (Guy Walenga, Clemson Tire Conference, March, 2004)

2. Despite repeated advice from consumer and industry groups, fact is, consumers simply do not check tire pressures regularly (you can forget about monthly checks). People just don't have the time and that is unlikely to change soon. When did you check your tire pressure last? According to studies, a large majority of us (~90% in a report by RMA http://www.goodyear.com/media/pr/nat_2003/22655ti.html ) do not check our tire pressure properly. So, many of us are likely riding on underinflated tires. If Nitrogen tire inflation can reduce that underinflation effect, it contributes, even if modestly, to improved gas mileage and ride comfort. Mileage improvement stories listed here are likely factual and these people, like many others, were riding on underinflated tires and nitrogen tire inflation helped, just like air inflation would have. But with nitrogen, proper inflation may last just a little longer.

3. Even CR test does shows ~38% improvement in pressure retention with nitrogen. If average tires lose 1-2 psi per month, compounded difference over 4-6 months may be well over 4 psi.

4. Another perspective is its impact on energy conservation and climate change. In that regard, individual paybacks become less important than overall contribution to reduced energy consumption. Examples are energy saving light bulbs and hybrid cars with long paybacks.

5. There should be no doubt on whether nitrogen tire filling is better or not. It definitely is. Question should be if it’s worth the price charged? May be not for everyone. It should be looked as a matter of convenience. If you do not have to top off tires as often, is it worth it the charge?