Nitrogen is a larger molecule and therefore takes more time to leak
out. As the water wapor is in the gaseous form it behaves like any
other gas. 18 grams of water takes up 18cc but 18 grams of water vapor
takes up 22.4 liters of space at STP, a 1200x expansion. Thank God that
water is typically a liquid at standard temps and pressure as going to
the beach would be quite an adventure if it wasn't. The problem with
water in your tires is the volume loss when the water vapor condenses or
even more critical the volume gain when it goes from liquid to gas which
will cause the pressure to climb rapidly if a substantial amount of
water is present. You should flush the tires a few times if you are
going to N2 to get rid of the O2 and H2O vapor, or I would think pulling
a vacuum and filling with N2 would accomplish the same thing, maybe
better. Or like millions of Americans with underinflated tires, don't
worry, be happy.
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