I didn't think of this at first, but...

The belt under the wheels won't be perfectly straight, it might
sag due to forces like gravity. Rockering the wheels would help
with that, but causes loss of control at high speed. Rockering
helps with maneuverability (that's the problem when going fast,
involuntary change of direction). But the inability to steer is a
potential problem with a tank tread anyway. Just can't go fast,
but that's okay given the risk of the belt breaking. A more likely
drawback of rockering is the loss of benefit from inline wheels,
the ability to smoothly roll over pits and potholes. As I recall,
rockering is for maneuverability. Maybe a little rockering towards
the back would work. In addition to helping solve the sagging belt
problem, rockering towards the back might reduce the ability to
smoothly traverse potholes but it might enable steering.

The term "rockering" means raising the front and back wheels on an
inline skate.





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Either the belt, or the staggered wheels thingy.
Thanks to the replies.