Stupid question about tires

DrewE wrote:
Water vapor not near the dew point does indeed act as an ideal gas, for practical purposes.

Air from a compressor (at least in somewhat humid climates), if there is no dryer in the line, will be saturated and pretty close to the dew point at the tank pressure, as evidenced by the condensation that collects in the compressor tank. Tire pressure is lower than the tank pressure, which lowers the pressure dew point in the tire somewhat, but it's still well in the range of ambient conditions that a tire is likely to be exposed to.

While rubber is somewhat more permeable to water than to air, it's still a very slow process for it to get out. (It's still more permeable to carbon dioxide, and it takes a long time for a tire filled with that to deflate noticeably.)

I have flipped a lot of tires back in the day when it paid my rent. Never any moisture ever. Tires are always dry inside. This in the 1980s when no attention was paid to use nitrogen, use an air drier, separator or filter. Just compress to 175 psi and fill the tire to 32. Drain the shop compressor when it seems to be short cycling. No perception of moisture in the tires.

I just use compressed air - and you will need some goof-off to remove those dumb stickers...

I'm just curious...how much do they charge to put nitrogen in your tires. Anybody know?? Do they meter it? Flat fee?
JK

Depends on the shop - some are free, some charge a couple bucks. I think I paid $5 a tire a number of years back, but have never paid since as other places are free. Although I have only done it twice and the last was Costco which was included with the tires. But the tires were cheaper at Costco vs Discount Tire.