Lordie, no--we had ENUFF trouble with Stepneygate!

 

Calculation is rather straight forward. Just look up the vapor pressure of water at the two temperatures of interest, then subtract. (Handbook of Physics and Chemistry). But recognize you have to have enough liquid water in the tire to actually saturate the entire volume at the vapor pressure, kind of doubtful.

I too use an old fashion high volume bicycle pump. About 6-7 pumps per psi. (15 in. tires on a MC). If one is that worried about water vapor, just pump up your tires with a bicycle pump on a very cold dry morning, when the dew point is in the teens. The air is pretty dry then. Don't pump it up when its raining (air saturated), or there is fog, or significant dew on the grass in the morning.

 

I agree. I think I'll stop now while I think I'm ahead.

 

Most shops that run equipment off their air compressors will usually have an inline dryer to catch most of the moisture in the lines/compressed air, which is a lot less effort.
When I was working on PCA racecars we used bottled nitrogen for everything from the tires & shocks to the built-in jacks. You still get some pressure change as the tires heat up, but it's more consistent, no need to debate the physics.

Having your pressure change as the tires heat up is NOT an old racers trick, it's just something you have to deal with/account for, same as the tires adhesion as the rubber changes temp. In an ideal world you'd have nice sticky tires from the time the green flag to the checkered.

In a street driven car your tire pressure's going to change more based on the ambient temp. then your driving style, not worth worrying about. If you're really ****, spend that $40 on a good pressure gauge and check your tires on a regular basis. A nice gauge will last you the rest of your motoring lifetime.

 

Good to know about the in line dryer.