Those are fascinating. But while I was thinking about why they seemed like they’d be heavy, I came up with a completely different thought.

A traditional circular wheel is kind of wasteful of material and space. At any given time the bottom spikes are doing the largest strain and only a few inches of tire are touching the ground. The wheel is in compression and hardly strained at all, which is why it’s ok to make it from aluminum. What if the wheel and tire were replaced with a little tank tread? Half a foot long. Could you make it have a similar rolling resistance? You could have a fork as big as the one on a Razor scooter, and suspension to stand in for the lost pneumatic tire.