Nitrogen tire pressures

[xtn]

Originally Posted by FlyLo

Only if you're getting a phase transition. Water vapor is still a gas.

To be fair, I have seen liquid water come out of gas station air pumps.

#1. A phase transition isn't required. Water vapor, as a gas, expands a lot more than dry air with the same temperature increase.

#2. OMG just imagine actual liquid water in the tire! Well I don't know how much that would contribute. Once the air in the tire is at 100% humidity, especially at 30psi or thereabouts, you're going to have to have a lot of temp gain for much more of it to vaporize. Of course, there may BE a lot of temp gain, but then again the pressure is going up with the temp, so I don't imagine more of the liquid water changing state.

Conclusion: Most of the pressure increase that is due to a heated tire may be contributed to the water vapor that is in the tire.

[SirBedevere]

Don't forget that when you "fill with nitrogen", you should have first evacuated all the air with a vacuum pump. If not, you still have a lot of air in there.