Our kids are starting to outgrow our double stroller, but will still want to ride from time to time. We've had this wagon for years, but it needed some upgrading. Rather than toss it and buy a new kid wagon, I decided to modify this one. Its biggest deficit was its wheels. They had metal sleeve bushings instead of real bearings and the wheels themselves were basically just an ABS doughnut with a narrow/thin rubber bands for tread. The treads had all cracked and fallen off. All this made the wagon hard to pull and loud.
I decided to make my own wheels to solve both problems. The new wheels consist of two halves and a TPU tread. The halves are keyed to mate with each other and are held together with m3 nuts/threadserts. Each half contains two skate bearings, resulting in four bearings per wheel. It's probably overkill, but I didn't want to leave the two halves unsupported in the center of the wheel at their interface.
Built in bridges for the somewhat weird shape to trick the slicer.
Now my 3 year old can pull me around in the wagon.
Near the bolt holes joining the two halves, you can see thin strips going across that overhang gap. Those eliminate local sagging without needing support material. The part could have been flipped 180 instead, but then the outer edge rim would be unsupported.