Wheels
There are two type of road wheels on the Kettenkrad, the spoked wheels are very easy to modify, just glue them together.
The more solid road wheels require a bit more effort. You need to cut a 18mm length of 1/2 inch brass pipe, file around the bush where it meets the back of the wheel to remove the paint.
The tube is slightly too small and will provide a push fit, as you can see.
Tap the tube on to the bush, then run a small amount of super glue around the gap between the inside of the tube and the bush.
On the other half of the wheel apply some super glue to outside of the bush and then tap the two halves together, make sure they run true to each other by spinning them.
Allow super glue to dry before reassembling back on the Kettenkrads axels.
The tube size that I used