Air at 20C at normal atmospheric pressure is 1.204 milligrams per cubic cm. Not very much.....40psi is about 2.66 atmospheric pressures, so I would guess that at 20C 40psi air weighs about 2.66 x 1.204 = 3.211 milligrams per cm3.
Not very much. So a 14" tire would probably hold about/approx/educated guess, maybe 5 liters??? or 5,000 cm3. Weight of the air maybe would be about 16 grams. Not very much....??? Am I close??? Even at 10 liters of air, 32 grams???? Not very much..