PDA

View Full Version : Nitrogen in Tires?



wnelms
02-08-2006, 05:22 PM
Hello gang. I was recently in Costco, and I saw a service brochure that recommended inflating tires with nitrogen as oppose to air (oxygen/nitrogen/etc.). Costso claims that pure nitrogen does not escape as fast from tires. Hence, the characteristics of nitrogen help maintain better tire pressure and as a result one gets better tread wear and more miles from a set of "shoes".

By the way, their pricing is very competitve as it includes "road hazard". Please note that Costco told me it would take them about two weeks to obtain the tires for my vehicle - 235/45/17 Michelin Pilots. Price $173.

Is this simply a marketing ploy or is it vaild science?

1996 328ti
02-08-2006, 11:09 PM
The deal with nitrogen is that it doesn't change air pressure with temperature.
I think cars in storage can benefit from nitrogen. For a passenger car I think it is a gimmick. It couldn't hurt. But I don't buy that it leaks less than air.

Dirichlet
02-09-2006, 08:01 AM
The deal with nitrogen is that it doesn't change air pressure with temperature.


This isn't true. Any gas will increase in pressure when it's temperature is increased, given that the volume is held constant. P=(nRT)/V...

1996 328ti
02-09-2006, 08:46 AM
This isn't true. Any gas will increase in pressure when it's temperature is increased, given that is volume is held constant. P=(nRT)/V...Maybe I'll rephrase it. It doesn't change as much. This is why race cars use nitrogen.

spric116
02-09-2006, 08:54 AM
I don't have any experience with pure nitrogen in tires, but air is ~79% nitrogen, isn't it? and about 20% oxygen, with a bunch of others making up less than 1%. And I think nitrogen and oxygen molecules are pretty close to the same size, so it doesn't seem like there would be too much difference between pure nitrogen and air...

Its been a while since chemistry though, so I could be wrong.

SharkD
02-09-2006, 09:01 AM
This isn't true. Any gas will increase in pressure when it's temperature is increased, given that is volume is held constant. P=(nRT)/V...
That's the ideal gas law, van der Waals takes into account the fact that moleclar structures are not uniformly elastic and/or symmetrical:

http://hyperphysics.phy-astr.gsu.edu/HBASE/kinetic/imgkin/waals.gif

(R is the universal gas constant, A & B are gas-specific constants)

Oxygen (a)1.382 (b)0.03186
Nitrogen (b)1.370 (b)0.03870

Basically, Oxygen and Nitrogen are relatively similar, and the issue is moot, anyway, since ~79% of the atmosphere is nitrogen. (Edit: spric116 beat me to this point.)

AlfaEric
02-09-2006, 10:09 AM
I don't have any experience with pure nitrogen in tires, but air is ~79% nitrogen, isn't it? and about 20% oxygen, with a bunch of others making up less than 1%. And I think nitrogen and oxygen molecules are pretty close to the same size, so it doesn't seem like there would be too much difference between pure nitrogen and air...

Its been a while since chemistry though, so I could be wrong.
Nitrogen will leak less than oxygen (their molecules are slightly larger) but if the difference was actually significant you could do things this way... If you filled your tires and (to keep things simple) about 80% was nitrogen and 20% was oxygen (and other stuff)... If all the oxygen leaked out your tires would be left filled with mostly nitrogen (the original 80%). If you top off your tires you would now only have about 5% oxygen and 95% nitrogen since the original 80% Nitrogen would still be there... The next time there would only be about a 5% drop... The time after 1%... After a couple top-offs, your tires would be filled with Nitrogen. :tongue:

---Eric

wnelms
02-09-2006, 10:10 AM
I am glad to see that others are quite versed on the subject. From what has been presented, it seems that my only "real" issue is assessing whether Costco's customer service and price warrant me business. Thanks for the thorough explanation...This is truly an engaged message board!

Dirichlet
02-09-2006, 10:13 AM
That's the ideal gas law, van der Waals takes into account the fact that moleclar structures are not uniformly elastic and/or symmetrical:

http://hyperphysics.phy-astr.gsu.edu/HBASE/kinetic/imgkin/waals.gif

(R is the universal gas constant, A & B are gas-specific constants)

Oxygen (a)1.382 (b)0.03186
Nitrogen (b)1.370 (b)0.03870

Basically, Oxygen and Nitrogen are relatively similar, and the issue is moot, anyway, since ~79% of the atmosphere is nitrogen. (Edit: spric116 beat me to this point.)

Glad to see there is another scientist among us :)

AlfaEric
02-09-2006, 10:21 AM
Maybe I'll rephrase it. It doesn't change as much. This is why race cars use nitrogen.
The rubber and wheel will also expand/contract with temp changes. I believe the main reason race cars use nitrogen is because it isn't flammable.

---Eric

SMOODY
02-09-2006, 12:36 PM
From what I understand, the process to get pure nitrogen results in a dry (no water), inert gas. The lack of water vapor reduces the amount that tire pressures will increase as the tire heats up.

Does it make that much of a difference for the average daily driver? Probably not. But it sounds good.

I think that using nitrogen is really only beneficial in race cars and vehicles that need their tires to last a very long time. Most of us will wear the rubber off the tire before the tire breaks down from being filled with regular air. And as Eric noted, over time your tires are filled with mostly nitrogen anyway.