[Madidus_Scientia (OP)]

My friend insists that his mothers car is "so much smoother" after she had her tyres changed and filled with helium instead of air. I argued that the effect was more likely due to the brand new tyres rather than the helium, or placebo effect. But is there any reason for using helium instead of air or is the tyre shop just trying to con people out of money?

I know it would make the tyres slightly lighter than usual, but would this really be significant at all?

And helium atoms being so small, would they leak out of the tyre like they do out of balloons?

[Don_1]

I can't see this making the slightest difference.

[Bored chemist]

I think the answer to the question posed in the thread's title is "Yes, but only if you are the one selling the gas.

[lightarrow]

The only relevant difference is the fact helium doesn't have water vapour mixed with it (as instead in the case of air). Water vapour can cause greater pressure variations with temperature.
Another effect (of which relevance I really don't know) is the adiabatic compressibility as function of T and P (which depends essentially from the specific heats) which can give a different elastic response of the tyre and a different energy dissipation in the rolling and in compression/releasing. The last two tings depends also on the different density of the gas, because during tyre compression, the gas inside "squishes" laterally, so I presume a lighter gas would work better from this point of view (but, again, don't know the actual relevance of this).

[Karsten]

From: http://blogs.consumerreports.org/cars/2007/10/tires-nitrogen-.html

"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.

Nitrogen_tiresaver_4 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.

Nitrogen_mainchart_consumer 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."

[Karsten]

And from: http://www2.canada.com/calgaryherald/cars/story.html?id=c9300414-e397-48b3-8f6f-2b0410cdb66b

Q:What's wrong with air versus nitrogen? During a recent trip to my nearest tire store, to get a punctured tire repaired, I asked the customer service rep if he could give an estimate on a set of tires that I may have installed in the fall.

When I got home, I reviewed the estimate and noticed that he had added Consumer Nitrogen at $7 per tire to the invoice. What is this about? Is this another way to boast company profits?

I like the free stuff that you get out of an air hose, I find that it works just fine thank you. Why nitrogen? Why not pump CO2 into our tires? That way we could reduce global warming.

A: Our atmosphere is made up of approximately 78 per cent nitrogen and 21 per cent oxygen. All tires will lose pressure over time, as the oxygen makes its way through the polymer chains of the rubber in the tire. At the molecular level, nitrogen is slightly bigger than oxygen, and so nitrogen minimizes the loss.

Oxygen and moisture contribute to the degradation of rubber in tires. Nitrogen generators remove both oxygen and moisture. Therefore the "inside" rubber portion of the tire should degrade slower. The pressure of a tire filled with nitrogen is not affected as much from variations in ambient temperature or from heat caused by road friction and load. Nitrogen is currently used in aircraft and race car tires for these very reasons.

For nitrogen to be effective in the everyday automotive world, the rims must be free of corrosion on the tire to rim sealing surface, whether steel or alloy. This "corrosion-free" state may be hard to achieve on anything other than new or low-use rims that haven't seen wintertime road de-icing chemicals. Otherwise, the nitrogen will leak out the same as air.

In my experience, rim corrosion issues contribute more to low tire pressure than anything else. And most people simply do not check tire pressure often enough.

So, if nitrogen has all these benefits, why not use it? I would give it a try with a new set of tires.

I'm going to speculate that in the not-so-distant future, nitrogen won't be optional during a new tire installation, if one wishes to keep the manufacturer's tire warranty valid.

[Karsten]

In case of using nitrogen, it seems that checking your air pressure and keeping it where it needs to be (or even slightly higher) is just as effective and much cheaper.

[Madidus_Scientia (OP)]

Thanks Karsten

[Don_1]

As I said, the use of nitrogen to inflate tyres will not make the slightest difference, except to the cost of running.

The test Karsten referred to proves nothing whatever, since this was carried out under almost 'lab' conditions and the wheels were unused. Our roads are not 'labs' and tyres do get used.

Rim corrosion - Next time you have a tyre changed, look at the wheel while the tyre is off. You will see no sign of corrosion on the hub where it has been protected by the tyre. As for the actual rim of the wheel you will see that any corrosion will have occurred where the rim is exposed to the air. The majority of the rim is, in fact, exposed to the air. Most corrosion will have taken place at points where the rim has been damaged. If you are that desperate to avoid rim corrosion, don't bump your car up kerbs and/or fit alloy wheels.

Oxygen and moisture contribute to the degradation of rubber in tires. - A tyre will wear out long before there is any appreciable degradation of the rubber. I would hazard a guess that a tyre could do 10 times the milage its tread allows before any such appreciable degradation occurs on the inner surface of the tyre. Any appreciable degradation will occur on the outer surface of tyre which is exposed to the air, rain, grit, salt, oil and other muck on the road surface.

I think the answer to the question posed in the thread's title is "Yes, but only if you are the one selling the gas.

Quite so.

I'm going to speculate that in the not-so-distant future, nitrogen won't be optional during a new tire installation, if one wishes to keep the manufacturer's tire warranty valid.

I don't think so Karsten, unless tyre manufacturers get in on the supply of nitrogen, in which case I would agree with you.

[Karsten]

I'm going to speculate that in the not-so-distant future, nitrogen won't be optional during a new tire installation, if one wishes to keep the manufacturer's tire warranty valid.

I don't think so Karsten, unless tyre manufacturers get in on the supply of nitrogen, in which case I would agree with you.

I did not say that. That was from the website I quoted.

[Don_1]

Sorry, pardon Karsten.

[lightarrow]

And from: http://www2.canada.com/calgaryherald/cars/story.html?id=c9300414-e397-48b3-8f6f-2b0410cdb66b
...
At the molecular level, nitrogen is slightly bigger than oxygen, and so nitrogen minimizes the loss.

Is this really true? Since the O₂' molar mass is greater than that of N₂, I thought it would be the opposite (but of course it's not so simple).

[Karsten]

Sorry, pardon Karsten.

Thanks.  []