Nitrogen filled tires, Is it worth it?

[enigma9o7]

Assuming ideal gas, the R values cancel anyway, and the change in pressure is purely a function of the change in temperature.

PV=mRT. Same mass, Same volume, Same R values. Say T1 is 80F and T2=0F

I don't think mass is the same, that's the whole point. And I remember the formula as PV=nRT, where n is the number of moles, and is equal to mass divided by atomic "weight"..... air and pure nitrogen don't have the same atomic weight... so I don't think the same number of moles fill the same volume and the same temperature and pressure.....

Kinda funny the ideal gas law comes up now, just last weekend I was driving behind a car with the license plate "PVISNRT", it took me a couple minutes before it clicked... guy must be a chemist or chemical engineer!

[Alex3000gt]

I was saying a closed volume - where state one is at a temperature, T1, and state two is at a lower temperature, T2. If it is a closed control volume then the initial mass, m1, is equal to the final mass, or m2.

PV=nRT is the same thing as PV=mRT is the same thing as P=pRT.

When using mols R is kj/(kmol*Kelvin), when using mass it is kj/(kg*Kelvin), or perhaps even BTU/(lbmass*Rankine) depending on SI or US units.

Mass=mols*atomic mass in g/mol or kg/kmol.

[enigma9o7]

Exactly. The initial pressure and temperature are the constant right? R is the same thing if in the same units... but n, or m, or whatever - those are what's different between air and pure nitrogen. What is constant over over temperature between air and nitrogen in your tire is the volume. So if volume and (and R) are constant over temperature, what varies? With different n, it's the pressure! And thus, that's why some people prefer Nitrogen over Air. (Not considering that the nitrogen some people are buying is not pure nitrogen, I wasnt aware of that, but either case it's n is gunna be better than air).

I probably don't know what I'm talking about, this isn't my area of expertise, I'm an EE so I let the ME's deal with chem/temp stuff at work... but unless I'm misinterpreting the basics, I'm pretty sure I'm right. Plus its midnight on a friday night and I've been drinkintg. Well drinking. I coulda corrected it. But taht helps my point, I dunno what I'm talking about, it's just off the top of my head without thinking too hard. (And I could correct that too).