Adding air to RC tires would be rather difficult. When I raced electrics back in 87' we would glue the tires to the wheels and in some cases trap air inside. As I got out of RC's (and into girls) foam inserts were just coming into existence. If you notice there are companies that make various foam liners, hard, medium, etc. Foam liners do a very good job of acting as a replacement for air.

OHHHH one last thing. For any kid who is going down the path I went down (getting out of RC and into girls), BEWARE! As expensive as RC hobbies are, they are still CHEAPER and in some cases give you less trouble than girls!!!!!!!!!!!! J/K!!!!!!!! LOL!!!!!!!!!!!

Later.