Do they use helium in car tires?

Answer 1

Not normally. Most stations use just plain ordinary air. Some places are starting to use nitrogen in the tires.

those places that do use nitrogen, do so as to reduce loss of pressure over

a much longer time-period, as supposedly, the molecules are 'bigger-fatter'

than those in regular 'air' /so I've heard/--and 'those places' sometimes

replace the valve-stem-caps with bright green-ones as a visual tip-off,

although who knows if that nitrogen was replaced /for some reason/ by

yet another place, months later. one would hope they change the cap to

black again, if so air only was used to re-inflate.