It's easy to build a solid container with < 1 atm inside. But I don't think such a container will fit the definition of a pneumatic tire. Any flexible container

It's easy to build a solid container with < 1 atm inside. But I don't think such a container will fit the definition of a pneumatic tire. Any flexible container with < 1 atm inside will collapse until the pressure inside reaches equilibrium with the air outside. It will collapse further if there's a heavy load on top of it, or maybe less if it's a run-flat tire with rigid structures inside. Perhaps if you were on top of a very tall mountain or, even better, another planet, you could get away with filling your tires with less than < 1 atm and still have them functional.