Check tire inflation pressure (including the spare) at least once a month and before
every long trip. Tires must be checked when they are cold; that is, before they
have been run a mile. If you must drive over one mile for air, before you leave
home, measure the cold inflation pressure of each tire and record the actual under-inflation
amount for each tire.
Upon arriving at the service station, measure the inflation pressure of each tire
again, then inflate the warm tire(s) to a level equal to the warm pressure
plus the under inflated amount you measured when the tire was cold. If the cold
tire inflation pressure matches the placard recommendation, then no further adjustment
is necessary for the warm tire.