If the tires have calcium chloride inside, make sure the fluid covers the entire rim. This will prevent corrosion of the rim. You can by a gauge designed for fluid filled tires. They are made with non corrosive materials. The pressure will read the same with or without fluid in the tires. You won't have any fluid come out once you learn how to put the gauge on the valve stem properly. Put the gauge on squarely, press firmly, then remove quickly.