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

[bruce kepley]

First of all, I was extemely skeptical about filling my tires with Nitrogen but finally agreed to do so at the urging of a friend. These are my observations...

I have a 2005 Hemi Daytona truck...after filling with Nitrogen I noticed an audibly quieter ride and better handling. Suspecting that this was just me, I had a friend to do the same with his Dodge truck and he experienced the same, along with reduced pressure fluctutions over time and temperature.

About one year after filling the truck's tires with Nitrogen I bought a standard utility trailer 6x10 for my lawn mower. On the way home, unloaded, it was bouncing in an un-nerving fashion, so I stopped at the same place that filled my truck tires with Nitrogen and had the tires filled at no charge (primary reason was the reduction in "dry rot" for a sitting trailer). Immediately the trailer changed reaction to a smooth, even ride. I had a friend with me and we were so surprised and skeptical that we turned around and came back over the same road from the trailer place and the ride was still smooth. Shocked is a good word to describe how we felt.

In December, 2008, I bought a 61 corvette straight axle car, not noted for the handling. To make matters worse the tires were brand new bias belted, so they developed flat spots when sitting. After filling with nitrogen the cars handling characteristics improved dramatically to the point that my friends thought that I had changed the suspension. As well, the sound level was audibly reduced and no more flat spots. Why, I don't know, but this is real world to me.

So I have nitrogen in not only my truck, trailer and collector car but in everything I own, including my riding lawnmower, where it made the most dramatic change. Instead of bouncy it's a much smoother ride and I don't have to check tire pressure but once a year.

You guys can continue to shoot at Nitrogen, and I was just as skeptical, but I spent 30 bucks to see what all of the fuss was about. I now consider that a great investment.

Take your best shots...these are my actual experiences, not theory...

[Ken Westbury]

Seems that if the oxygen escapes through the tire and the nitrogen does not, eventually through the process of repeated filling, the tire would be 100% nitrogen anyway. Why pay for it?

[Mike W]

Everyone keeps saying that the air we breath is mostly nitrogen and why therefore would you pay for additional nitrogen in a tire. Let me ask a question. Would you drink a glass of water that contained 20% gasoline? No? Why not? It is mostly harmless water. That is the point. It is the 20% oxygen, co2, moisture, misc. gasses that adversly effect a tire, just as the gasoline would effect your health. Oxygen and moisture cause a chemical reaction know as oxidation. This is why paint peels, steel rusts, etc. You would not see those effects if they were subject to an inert gas only, such as nitrogen. Need I say more.

[Tom]

Why not use helium in your tires. Helium is used in ballons
and is lighter than air thus lowering the weight of the vehicle.

[Jay De Dabellue]

Tom, "...why not use helium?..."
Because helium will make your voice sound funny, and then the cops will throw you in the pokie. Okie dokie? JDW

[joe]

I am always amazed at how easily the public is duped into believing these marketing scams. Even if you slept through your high school physics class, you had to have absorbed some knowledge to pass the course. Or did you?

[jack]

"Seems that if the oxygen escapes through the tire and the nitrogen does not, eventually through the process of repeated filling, the tire would be 100% nitrogen anyway. Why pay for it?"

All atoms seperate there is not enough air to totally drive out all the air molecules without a complete and repeat purge.

[Jim Connell]

I recently had my 2009 Fusion tires filled with Nitrogen. The ride was so much improved and the handling so much easier that I then had my 2001 Crown Vic tires filled also. I had new Michelin tires on the Crown Vic and wanted it done immediately. The Crown vic has 114,000 miles and handles like a new car.

[yosef lati]

hi,i use to live in las vegas and i use the nitrogen air in my car working great.im living in israel now and i dont know if you supply any of the nitrigen air her in israel ?and if not i will be nice to sell it her,let me know what do i need to do to make it happend,thank you ,yosef

[Normfromga]

"Seems that if the oxygen escapes through the tire and the nitrogen does not, eventually through the process of repeated filling, the tire would be 100% nitrogen anyway. Why pay for it?"

'All atoms seperate there is not enough air to totally drive out all the air molecules without a complete and repeat purge.'

Ah, but the main argument for filling with N2 is that O2 leaves the tire up to three times faster. Thus, this filtration would enrich the N2 content over time.

Of course, there is a limit...even if you topped up with air every time your pressure dropped 3 or 4 psi (~10%), a little oxygen would be introduced.

However, 10% of 25% O2 (in air) = only 2.5% O2 in the tire, which means the tire could contain a purer N2 content than that used in the CU experiment (95%).

[FUNZIE]

Just another way to take money out of our pockets!

[Gary]

If this discussion were based on free air vs Nitrogen for free then the advantage would be to use the nitrogen because of the small advantages mentioned above.

But since the user would need to go to the dealer and pay for topping up there tire and also paid initially to have them filled, it has a disadvantage since the average owner can not just check his tires and air them up.

I think the advantages of regular inspection and topping up due to temperature changes and other issues out weigh the marginal advantages of nitrogen.

I think regular inspection and proper inflation with good old air is a more economical and better solution than wasting money and depending on the dealer. Proper maintenance is more likely with air.