A couple misconceptions need to be cleared up because you are a little misinformed. To begin, air is made up of roughly:
78% Nitrogen
21% Oxygen
1% Argon
There are a lot more components but they are in quantities so small we can assume they are all 0.

You fill up tires with a compressor. While they may very well have had an air dryer you are right in stating that it won't increase the amount of nitrogen any noticeable amount. They also may have had an air separation unit. It would be a huge waste of money, but they certainly exist.

Nitrogen and Argon are not "airs". They are gases just like propane, butane and the many other gases you see on a day to day basis. Oxygen and the trace amounts of water vapor at the low pressures that you are filling your tire are just as stable as nitrogen and argon. At low pressures (and high temperatures) gases will behave as an ideal gas (remember PV=nRT from chemistry?).

Individual oxygen molecules are slightly smaller than nitrogen, but only by about 3%. You will not see any significant differences using that as your reasoning.

There are several beliefs on why you should fill your tires with nitrogen. All of them are as dumb as the next.

Some people believe that not having oxygen in the tire will prevent it from rotting the inside of the tire. There may be some merit to this belief, but for nearly anybody the tread on the tire will go out long before any of the rubber begins rotting on the inside.

 

Yeah, I know. That's why I said "bet that 78% is a free fill up" - aka - from an air compressor. Thus the face.

Like I said, you're not increasing the nitrogen in the tire by *most* of the equipment that a lot of these tire shops are using to claim a nitrogen content in your tire. You're just removing the other stuff - moisture.

I'm not sure where you're calling me mis-informed - you just backed up everything I said - with an exception to me calling the other gasses "airs" - I typed that within the first 10minutes after my alarm went off. Trust me, not much thought went into it.

On a street car, there is not enough benefit to warrant putting nitrogen in the tire to be worth paying for. The race cars that I work on however, That is a different story. We do use nitrogen in our race tires for obvious reasons.

 

I may have missed it but when running nitrogen you need to start with a higher “base” pressure because it does not expand as its temp rises like “air” and therefore will not have the correct operating pressure if you don’t.

 

No, nitrogen will act the exact same as regular air. It will expand at the same rate regular air will at these low pressures.

 

Yes & No.

It's not something you should have to worry about in a street car at the very least. There's really no reason to have nitrogen in a street tire anyways. Any humidity thats compressed in the tire would only cause a minimal expansion & full temp anyways. Street tire temps are MUCH different compared to race car tires (where nitrogen IS needed) - where it NEEDS to be dry inside.

If a race tire hits a 2PSI change only due to the contents of the tire, thats major. We already have to start the tires at a lower PSI to compensate for normal temp build up during a race - it'd be even worse if we ran regular compressed air. A steet tire doesnt get anywhere near the same temps, and any psi change wouldn't even be noticable from the cab anyways...

Try driving a race car that should have finished a run at 29-30psi, and have it balloon out and hit 35psi...

 

Not in my racebikes it doesn't.

 

sqidd - I dont know if he's reading out of a science book quoting "perfect oxygen" or just compressed air in general. Not sure what he's thinking...

I completely agree with you - compressed air versus nitrogen do NOT expand at the same rates. The only difference is that I'm sure your race bke's tire temps get a TON hotter than your truck tires. I know my late-model race car tires do!