I had to go back to figure out why this thread became a talking point about global warming.
Low tires decrease mpg. 
Ice can sometimes get form in the valve stem area in freezing temps and cause a tire leak. Dry all the valve stems out and put new caps on and keep them tight. Might help.
GeorgeSanJose said: “Ice can sometimes get form in the valve stem area in freezing temps and cause a tire leak…”
Ice can sometimes form in 37°F temps, so I recommend NOT checking tire pressure when it is below 40°F
^Go all winter without checking pressure? I recognize your expertise, but that seems…extreme.
I’m interested in this ice that forms at 37F. You could win a Nobel Prize for this discovery.
The air coming out of the compressor can be much colder than the ambient temp. In cold weather I agree you need to be careful with moisture. I always let a little more air out of the tire before adding air just to make sure frost is cleared out of the valve. But then I have a warm garage too and would never use an outside air source in the winter unless I had to.
"The air coming out of the compressor can be much colder than the ambient temp."
It would only be about 3 deg F colder from a 140 psig compressor.
@idiot,
Ever heard of adiabadic compression? Pressures go up/down; so does temperatures. Actually, I’m surprised letting 36 PSI out of a tire only results in a 5F drop!
"Ever heard of adiaba[t]ic compression?"
Actually, since the air does no net work coming out the valve, adiabatic expansion doesn’t play a role. Only the Joule-Thomson expansion coefficient applies. If air were ideal, there would be no cooling, but since it has a positive coefficient of about 0.25 K/bar, you see the minor cooling I mentioned above. Helium or hydrogen would warm slightly coming out the valve because they have negative J-T coefficients.
meanjoe75fan said: “…^Go all winter without checking pressure?..”
I didn’t say that. Surely there are times where your car in parked where the temp is above 40F sometime in the winter.
Idiot666 said: “…I’m interested in this ice that forms at 37F. You could win a Nobel Prize for this discovery…”
atmos.washington.edu/cliff/Roadway2.htm
Extracted from that: “…Thus, frost can be occurring at the surface even when official temperature observations are reporting temperatures of 35 to 37F…”
And as been been mentioned above, air escaping from a high pressure to a lower pressure cools and can form ice.
Actually both disprove your point. Joule Throttling lowers the temperature. Official temperature stations are set like 6 feet high so it is not measuring the road surface temperature. Plus the weather station can be many miles away. In either case, the water is not freezing at 37F.