Some basic things to do with "air" style hubs. Always glue the tyres to the hubs, just on the outside of the rim. Then true them up and if you treat your tyres (rubbing oil in to them) do that. This overall affect will creat a pocket of air in the middle space that expands as the rotational speed increases (down a straight) giving a larger diameter and more top speed. Round the corners it "deflates" and gives max surface area round the grips and therefore max grip. It is known to inject air in to the centre part of the tyre to aid this but this only works if it is a totally sealed unit.