Inner tubes are part of the rotating mass, and therefore they should be as lightweight as possible. But they also have to be plenty tough as a flat easily eliminates any gain in time.
Additionally, thicker inner tubes are being used during practice. This is why Onza Tyres offers its BMX inner tubes in two wall thicknesses, the ones for road bikes in three and the ones for mountain bikes even in four varieties. That way, you have the freedom of choice.
Buy Onza Wheels & Tyres from Chain Reaction Cycles, the World’s Largest Online Bike Store.