Quote Originally Posted by angrybear View Post
No they should not leak

Neither should your tyres,
but they will be effected by temperature ie if you fill them at a garage while hot from driving when they cool the pressure will drop, also the weight of the vehicle (loaded/unloaded) exerts physical load on to a tyre allowing/preventing expansion of the rubber.

Tyres leak - other than through a faulty valve or cracked wheel, there's a large mating surface between the tyre and wheel which leaks when the wheel coating starts to corrode...but the oxygen molecules in air slowly permeate through the tyre rubber. The valves at the fill end and outlet end of an air rifle are the only component in common with a car tyre and if they are leaking there's something wrong with them.