Using air + castors/wheels is an interesting combination. I imagine it must be on the light side of feathers though, to get a decent speed, but also not too much momentum/inertia (always forget the correct word for that) to be too difficult to quickly change direction if you're heading for disaster (say a pit)?

Using air is something i'd considered, but didn't give much though, as I expected the driving to be worse than trying to drive a piano down a hill.