I know the spares used to be filled with nitrogen, but I'm not sure about the primary tires.

 

You still have a leak.
The "nitrogen-fill" tires will be a bit more PSI stable under varying temperature conditions, that's all.

 

Nitrogen is just a gimmick in my opinion. So the two arguments for nitrogen are that 1) it is dry and doesn't have water vapor and 2) it permeates through tire walls more slowly than oxygen.

A common "pro" given for nitrogen fills are that oxygen can permeate through a tire about 3 times more rapidly than oxygen. But the key thing to take into consideration is that the permeation of oxygen through the tires is very small anyways. Combine that with the fact that filling your tires with standard compressed air will consist of only ~20% oxygen.

The "nitrogen-fill" tires will be a bit more PSI stable under varying temperature conditions, that's all.

Nitrogen filled tires won't be any more PSI stable over temperatures compared to standard air filled tires. The only reason its claimed that nitrogen tires are more temperature stable than standard air filled tires is that the nitrogen is dry and doesn't contain as much water vapor as standard air. But if you fill your tires with a well maintained air compressor that has a drier on it, you will be fine. The key is to use a compressor with a large enough tank. Because if you let your compressor's tank pressurize, the water vapor should condense and settle at the bottom of the tank, and the output air will be pretty dry. Then when you are done filling your tires, drain your tank to get rid of any water condensate.

 

Keep in mind shop air is going to already have about 78% nitrogen. Our atmospheric air only has about 21% Oxygen, 78% nitrogen and the rest is CO2, Ar and trace elements. We are already getting nitro fill, no need to pay extra for it.

 

I don't know about saying temp variations make no difference between nitrogen and air.....In the midwest we get 50° temp swings all the time, especially when coming out of winter. I've had much more "even" tire pressure since a free nitrogen fill over plain air...... Others in the area have similar experiences. I think it depends a lot on your climate.

 

I was just trying to say that correlation does not imply causation. Nitrogen filled tires are correlated with lower pressure differences at different temperatures, but nitrogen is not the cause of this effect.

The temperature / pressure variation is 100% due to water vapor in the tire. It just happens that nitrogen production systems produce very dry nitrogen. Thus, nitrogen filled tires usually have less water vapor in them, so the tire pressures have a lower temperature dependence compared to air filled tires (which usually have more water vapor in them). You can achieve the same temperature stability if you use an air compressor that is drained frequently and has a drier on it.

Gay-Lussac's Law applies whether you have pure nitrogen or traditional air

 

You just used the word "causation"...now you have gone above my pay grade Mr. Fancy Words

 

Tires filled with Nitrogen usually have green valve stem caps to alert the owner/mechanic to not use regular air. Mine had regular caps, I bet yours does too.

 

5th Gear on Nitro fill:

 

You still have a leak.

You are correct, sir or madam! Dang, that was one tiny screw. Was 600 miles from home when I discovered it, but I figured correctly it would last until I got home as it was probably embedded in that tire for a year (and I have the optional spare).