Nitrogen in tires

[hot_rod]

Change it?

WTF....Does it wear out or something?

[CamaroSkooter]

Originally Posted by jrisebo

Ok, thanks. Perhaps i should use helium for better gas milage, lol. Or hydrogen for a bit more power

Helium is lighter than air, so I can see where the concept comes from, however it's also a smaller particle than air which means it will "leak" from your tires at a much faster rate than normal air will.

If you want to eliminate how much air leaks from your tires, then you could go with Argon, but I imagine the fact that it's almost 3 times as heavy as Nitrogen means it might adversely impact your gas mileage. I doubt it would be by much, but I'm not nearly knowledgeable enough on how much the weight of the air inside a tire contributes to increasing or decreasing gas mileage...

[Offy]

Nitrogen is great for racing because it dosen't change with temperature change as regular air will. In racing a pound can effect the car's handling quite a bit. In a road car it is a waste of time & money. I've even heard salesmen tell people that nitrogen can prevent a tire from rotting cause a tire goes bad from the inside!

[camarozzzz]

Originally Posted by hot_rod

Change it?

WTF....Does it wear out or something?

OF COURSE!! Tires need to breathe too man!!! If you keep using stale Nitrogen they will asphyxiate!!!

No man, I am kidding! You don't need to change it! It is just the service departments trying to bait you into coming in so that they can drop a bunch of useless things on you!

I have 40 000kms on my car and my service tech JUST tried to sell me a transmission flush, radiator flush, basically the WORKS. Tried quoting me at like 650$ worth of service I did NOT NEED!

[tonyko1]

Not sure what tires you have, but the Pirelli handbook specifically states that nitrogen is NOT needed.

[Bobaloo]

Nitrogen use comes from the aircraft industry where landing struts are filled with nitrogen due to the extreeme temp changes in altitude and airports traveled to. Yes it is less suseptable to pressure/temp changes and because the molecules are bigger leakage is less likely. Just plain old air in my tires.

[scottyvegas]

Air here.

[rykeith]

Originally Posted by scottyvegas

Air here.

Does that Barbie have a Kroger card?

[scottyvegas]

Originally Posted by rykeith

Does that Barbie have a Kroger card?

Yes, 10% off anything over an 8ball

[1o.f00t.570rk]

Your time/money would be better spent making sure that the air lines being used in the shop have the appropriate filters so you don't pull any oil or water.

That said, I'll add this to quantify the discussion:

Going into the math of the stuff, I submit the following equation:

PV = nRT

P = pressure
V = volume
n = moles of gas (unit-less quantity)
R = gas constant
T = temperature

This is the Ideal Gas law, which gives us both pressure and temperature in one equation. This equation can be simplified, however, for comparison and when trying to solve for a change in variables. We will pretend that our volume is constant, that we have exactly one mole (6.02 x 10 ^ 23 molecules) of each gas, and also that the gas constant is...er...constant. We'll drop those values out for the sake of comparison, giving us the following:

ΔP = ΔT (Conceptually)

Or

P1T1 = P2T2 (Mathematically)

Or, in words, the change in pressure at constant volume for a fixed quantity of gas is directly proportional to the change in temperature of that gas. We'd need to throw the constants back in if we were to calculate it out for the sake of getting units to cancel, but from a theory standpoint the relationship is accurate. This relationship also exists for volume and temperature at constant pressure, via Charles' Law.

We'll now need to bring in another concept, the one which helps quantify what ΔT means: heat capacity. Heat capacity is the measurement of how much energy is required to raise the temperature of a substance by a degree. The heat capacities of the two gases are as follows, assuming constant volume (and 298K):

Nitrogen - 20.8 J / (K × mol)
Oxygen - 21.0 J / (K x mol)

J = joules
mol = moles
K = ΔT, or temperature change, in Kelvin

So what this means is that it takes Nitrogen 0.2 J less at 298K (~77°F) heat up one degree Kelvin than Oxygen, if we assume we have one mole of each. This makes sense because there is more mass in O2 than N2, so the molecule with less mass requires less energy to change its temperature.

Now, let's assume that a car tire has a volume of 10L. We can then calculate how many moles of each gas we would have at a set temperature (298K for consistency) and gauge pressure (240kPa or roughly 35psi):

Nitrogen
240kPa × 7.9L= n(8.314(L × kPa)/(K × mol))(298K)
n=0.765 mol


Oxygen
240kPa × 7.9L= n(8.314(L × kPa)/(K × mol))(298K)
n=0.194 mol

The nitrogen component requires about 15.9 J / K, and has a mass of about 21.4 grams. The oxygen component about 4.1 J/K and 6.2 grams. Combined, the mixed gas would require 19.97 J / K to measure a uniform increase by one degree Kelvin, and total mass of 27.6 grams.

For comparison, pure nitrogen would be about 20.1 J / K and 26.9 grams, and pure oxygen would be about 20.34 J / K and 30.7g.

What about at a higher temperature you ask?

The heat capacity does change as temperatures also increase, but it does so in a pretty consistent pattern, though not identical for each gas. At 375K (202°F) the values look like this:

Pure Nitrogen - 28.1 J / K

Pure Oxygen - 28.7 J / K

"Air" - 28.1 J / K

So...while I could try and calculate exactly how much pressure was going to be exerted by the change in temperature of just the oxygen instead of the uniform gas, I won't, because tires are not a rigid container and things get wacky when you can have variable changes to both pressure and volume at the same time, especially by external means such as turning hard in a corner.

That said, you'll also note that the ideal gas equation doesn't really take into account what gas you are using, just that you have an ideal gas, which both nitrogen and oxygen can be treated.

At the end of the day, the math doesn't support some of the claims people make, and the rest exist in an area where the placebo effect has to be taken into account, because there is no actual way to quantify there being any change.

Now...move outside nitrogen/oxygen, or any ideal gas, and it becomes a while different ball game.

References:
http://en.wikipedia.org/wiki/Ideal_gas_law
http://en.wikipedia.org/wiki/Ideal_gas_constant
http://en.wikipedia.org/wiki/Molar_heat_capacity
http://en.wikipedia.org/wiki/Avogadro_constant
http://en.wikipedia.org/wiki/Ideal_gas
http://en.wikipedia.org/wiki/Gas_laws
http://www.engineeringtoolbox.com/oxygen-d_978.html
http://www.engineeringtoolbox.com/nitrogen-d_977.html

[rykeith]

Originally Posted by scottyvegas

Yes, 10% off anything over an 8ball