Does a car tire weigh more with air or the same when its flat and tire is on a rim?

The chemical signature for air is H20, or 2 parts Hydrogen and 1 part Oxygen. As each of these elements has mass, even in a gaseous state, the short answer is that air weighs 0.070 lbs oer cubic foot. So at one atmosphere of 14.7 PSI (that is the pressure of the air around us) when the tire is flat, if you knew the volume of the tire, you could compute the weight of the air in the tire.

Now, if the tire were inflated to 26 PSI, it would be at 1.77 atmosphere, so the weight of the air in the tire when inflated would more than when it is flat.

No, H2O is the chemical signature for WATER.

Otherwise the answer would be correct.