I vote for no air inside.
Ever play pinball?
Imagine the ball is a molecule of air. Lightly shoot the ball so it doesn't quite go over the top. It rolls smoothly back around to the plunger, right?
Now take a full shot so it enters the playing area (imagine that as the inside of your bike) and watch it bang off all the bumpers, cushions and flippers and slowly make it's way to the bottom.
Be kind to air molecules.