Driving on Nitrogen-Pumped Tires

[Richard W]

The Feedback section of New Scientist (the jokey page at the end) has an item about garages charging extra to fill tyres with nitrogen rather than air. When talking about why you might want this, they refer to "an extensive and non-converging discussion on the urban legends website www.snopes.com" - in other words, this thread:

http://message.snopes.com/showthread.php?t=19107

Apparently they thought the most convincing reply was Quidam's about water vapour...

Originally Posted by ghostwaste

Consumer Guide did a test on this. They left one tire inflated for a year with air, and one with Nitrogen. The tire filled with air had leaked out about 4psi, and the Nitrogen tire leaked out about 2psi. Not much of a difference, especially for a year's span of time.

That lines up with my experience. Leaking out at half the speed seems like enough of a difference to me. When I last bought new tyres, they put nitrogen in them without consulting me. I was annoyed at first, but I follow their instructions and go back once every 5-6 months for a free top up. Whereas previously I was getting my hands dirty every 2 months or so.

[SplishFish]

Originally Posted by Doohickie

The only reasonable explanation I've seen as a nitrogen benefit is that it doesn't leak as readily. But as was pointed out above, it occurs in smaller molecules than oxygen, the next most likely element in air, so it's hard to see how that is a benefit. There is a very small weight benefit since N weighs less than air, and in the microscopic margins of airline profits and space travel economies, it makes some sense to use it, but on a car I can think of no reason why nitrogen is better than air.

On a side note, Easy Spirit shoes has an AntiGravity line where the soles/heels have nitrogen-filled micro-bubbles that supposedly make the shoe lighter. I did buy a pair (because they were nice and cushy) but I can't feel any difference in weight between that pair and a pair of similar, non-nitrogen sandals.

[Squirt]

Dry air has a density of about 1.275 g/l at STP, and pure nitrogen has one of 1.251g/l at STP, so you'd need to have 40 litres of bubbles before there was even one gram of difference! Of course, bubbly rubber would be significantly lighter than non-bubbly rubber, but the difference in the weight of the bubble filling would be negligible.

[compass]

One of the Last Word columns in New Scientist was a question of whether helium filled marshmallows would float. Considering a helium balloon's lifting power, the answer is yes if they're approx balloon sized.
Unless they're meaning that nitrogen is used to make the bubbles, and taking advantage of the suggestion they're then lighter-than-air.

[Alchemy]

Originally Posted by SplishFish

On a side note, Easy Spirit shoes has an AntiGravity line where the soles/heels have nitrogen-filled micro-bubbles that supposedly make the shoe lighter. I did buy a pair (because they were nice and cushy) but I can't feel any difference in weight between that pair and a pair of similar, non-nitrogen sandals.

Marketing people seem to like the word "nitrogen" so it's used in places where it's technically correct but highly misleading.

Expanded plastics like the above are made by mixing molten polymer with something that will create gas bubbles, which will remain when the molten polymer solidifies - a lot like you'd make bread or a cake. Air isn't an option here; at the high temperature you need for keeping the stuff molten, oxygen in these amounts would just char the stuff.

And still, the "nitrogen" they refer to is almost certainly not nitrogen gas; it's some organic compound that happens to contain nitrogen. (Which is, to some degree, like referring to a glass of water as "hydrogen enhanced." The element nitrogen is there, but the wording is misleading by suggesting a product contains gaseous (molecular) nitrogen, when in fact the product contains a chemical which happens to contain one or more atoms of nitrogen.)

"Nitrogen enhanced fuels" are much the same deal. They are a misleading marketing name for a fairly effective breed of gasoline detergents. "Amine detergent additive" would probably not sound as good as good. An amine is a particular type of nitrogen-containing functional group, which is part of some detergents. It sounds too chemical, like something you wouldn't want. Nitrogen sounds environmental, so that's the phrasing they use when marketing their gasoline to the general public.

[BoKu]

Originally Posted by Alchemy

...It sounds too chemical, like something you wouldn't want...

Hey, you got amines in my Bisphenol-A!

[Alchemy]

Originally Posted by BoKu

Hey, you got amines in my Bisphenol-A!

But it comes with a free Frogurt!

The use of Nitrogen in tires is primarily for two reasons:

1) The absence of oxygen inside the tire prevents rubber oxidation from inside. This marginally (is believed) affects tire life.

2) The process by which Nitrogen is extracted removes 99% of all other things including moisture.

It has nothing to do with changing pressures based on temperature. Boyle's gas law refutes that. All gasses (within a tiny percentage) respond to the same exact formula: PV = nRT. As temperature changes, pressure changes proportionally regardless of the gas. The only reason pressurized ambient air in a tire would change pressure is if a considerable percentage of that air were water. Using Nitrogen in tires reduces the chances of moisture which reduces the chances of tire pressure changes based on temperature. It is also believed (as said above) to increase tire life by removing the possibility of oxidation from the inside.

[jimmy101_again]

Originally Posted by Doohickie

n does not change for gas in a closed system (such as a tire with no leaks)

As others have posted, moist air over a wide range of conditions is not well represented by the Ideal Gas law. Primarily because "n" is not constant. (Condensed moisture is not covered by the Ideal Gas law and condensation changes "n".)

Edit: One reason for not using compressed nitrogen in a tire is the huge difference between the pressure in a typical compressed gas cylinder containing nitrogen and the typical shop compressor. Shop compressors generally are limited to tank pressures of 100 to 150 PSIG. Cylinders of compressed nitrogen run from about 2000 to 6000 PSI. A car tire might explode at 150 PSIG, it absolutely positively will explode at >2000 PSI. So if the tire shop's Nitrogen pressure regulator fails, and the shop has a studly Nitrogen distribution system, there's a chance of a pretty respectable explosion.

[A Turtle Named Mack]

CO2 should work every bit as well as N2, maybe better since it is denser. And it could be very easy to apply, if we had tires with pressure relief stems - when the tires are mounted, just put a big chunk of dry ice in them, and as the CO2 turns to gas, it will drive out the O2 and H2O and keep the tire at the proper inflation pressure - what a sublime solution!

[GenYus234]

Booo! Hisss!

Did you come up with that idea just so you could say that?

On a serious note, I'd be concerned that the dry ice would make the tire brittle in that particular spot. Plus, the gas pressure might not increase fast enough to seat the tire on the rim.

[A Turtle Named Mack]

Originally Posted by GenYus234

Booo! Hisss!

Did you come up with that idea just so you could say that?

No, but after dismissing the practicalities of it - your criticisms are among several I came up with - I posted anyway for the pun.

[overyonder]

Originally Posted by jimmy101_again

Edit: One reason for not using compressed nitrogen in a tire is the huge difference between the pressure in a typical compressed gas cylinder containing nitrogen and the typical shop compressor. Shop compressors generally are limited to tank pressures of 100 to 150 PSIG. Cylinders of compressed nitrogen run from about 2000 to 6000 PSI. A car tire might explode at 150 PSIG, it absolutely positively will explode at >2000 PSI. So if the tire shop's Nitrogen pressure regulator fails, and the shop has a studly Nitrogen distribution system, there's a chance of a pretty respectable explosion.

How often does one walk away from a tire being filled, or worse, let it get overfilled knowingly? Assuming either air or N2.

I have a few high pressure regulators in my garage (for welding, carbonating, etc) and all of them have release valve to "dump out" in case the regulator goes on the fritz.

OY

[Latiam]

Are people still charging for the nitrogen fill? When I got my new car in April it just kind of came with nitrogen filled tires. I had no real interest in them. I don't do anything to them and they check the pressure and add gas as needed during oil changes and maintenance (I haven't had any maintenance yet, obviously). It's included in the "Fluid top up" and that's included. (I was going to say free, but TANSTAAFL)

The car salesman did deliver it as a selling point but when my response was, "Oh. Really?" in a tone that made it clear that I was completely unfamiliar with the concept he wisely switched over to neat things I did care about, like heated side mirrors. (It does get cold enough and snowy enough here that that matters - ever try to use an ice scraper on a mirror?)

Even after reading this thread I'm take it or leave it. It's not something I'd pay for. It was included in the cost of the car, not an add-on.

The only annoying thing was that the valve caps have "N2" on them and someone stole one. They replaced it and gave me an extra, though, so that's fine. Probably happened in the school parking lot, since they're shiny. Kids.

[jimmy101_again]

Originally Posted by overyonder

How often does one walk away from a tire being filled, or worse, let it get overfilled knowingly? Assuming either air or N2.

I have a few high pressure regulators in my garage (for welding, carbonating, etc) and all of them have release valve to "dump out" in case the regulator goes on the fritz.

OY

Tire explosions aren't exactly common but they aren't unheard of either. http://www.ncbi.nlm.nih.gov/pubmed/1854067
I would think most failures are due to a flaw in the tire or rim but at least some are from over pressurizing (for example to get a bead to seal well). Give the mechanic access to 6000 PSI instead of 120 PSI and who knows what'll happen? A very high pressure source will fill a car tire pretty darn quickly, a mechanic used to 100 PSI could easily blow a tire if he suddenly had 1000 PSI and wasn't careful.

You can get fixed output regulators but most regulators are adjustable. In a shop, with an adjustable regulator, you would need to lock the regulator to keep people from fiddling with it.

[jimmy101_again]

Originally Posted by Alchemy

And still, the "nitrogen" they refer to is almost certainly not nitrogen gas; it's some organic compound that happens to contain nitrogen. (Which is, to some degree, like referring to a glass of water as "hydrogen enhanced." The element nitrogen is there, but the wording is misleading by suggesting a product contains gaseous (molecular) nitrogen, when in fact the product contains a chemical which happens to contain one or more atoms of nitrogen.)

"Nitrogen enhanced fuels" are much the same deal. They are a misleading marketing name for a fairly effective breed of gasoline detergents. "Amine detergent additive" would probably not sound as good as good. An amine is a particular type of nitrogen-containing functional group, which is part of some detergents. It sounds too chemical, like something you wouldn't want. Nitrogen sounds environmental, so that's the phrasing they use when marketing their gasoline to the general public.

I would be very surprised if shoe (foam) manufactures are using "nitrogen" and not referring to bubbles. Including nitrogen gas, as bubbles in a polymer is pretty easy to do and has been done for decades. Indeed, I would think that if a gas is going to be introduced mechanically (as opposed to being created in a chemical reaction like bread rising) then nitrogen would be the gas of choice (dirt cheap, readily available, chemically inert, non-toxic, non-flammable...)

I don't see anything wrong with "nitrogen enhanced" fuels since the additives do indeed contain nitrogen. Being more precise (using "amine" instead of nitrogen) contributes nothing to the description since 99.9% of customers don't know what it means.

You could label a nitrous oxide system as "nitrogen enhanced". Not that that tells you anything. (Nitrous is used for a completely different reason than are detergents, Nitrous is part of the oxidizer and contributes a heck of a lot of energy to the combustion process.)

[overyonder]

Originally Posted by jimmy101_again

I would think most failures are due to a flaw in the tire or rim but at least some are from over pressurizing (for example to get a bead to seal well). Give the mechanic access to 6000 PSI instead of 120 PSI and who knows what'll happen? A very high pressure source will fill a car tire pretty darn quickly, a mechanic used to 100 PSI could easily blow a tire if he suddenly had 1000 PSI and wasn't careful.

Exactly how are you going to deliver 3000-6000 PSI of Nitrogen to the fitting on the tire? The vast majority of flexible hoses are rater 175PSI operating with a 300 PSI burst (I'm going from memory admittedly). If the hose gets pressurized to 6,000 PSI, it will immediately (and very loudly) burst.

I've had ONE tire explode on me (in my hand, in fact), which was a bicycle tire. It was VERY loud and scary for the 8-y-old that I was!

OY

[RichardM]

Originally Posted by A Turtle Named Mack

No, but after dismissing the practicalities of it - your criticisms are among several I came up with - I posted anyway for the pun.

I had to go re-read your post to get the pun. Now

[A Turtle Named Mack]

Originally Posted by RichardM

I had to go re-read your post to get the pun. Now

Not all punning is verbal slapstick.