Tubes are not part of the standard wheels by default. Nevertheless there are some applications when a mounted tube does make sense. In case you want to use your ballon wheels some place apart from civilization (say a desert or remote holiday area) a tube comes in very handy since it is much easier to fix than a broken tire's shoe, similar to a bike. This is especially important for racing buggy pilots who spend a lot of their time apart from touristic areas pursuing their favorite sport.