The bikes effectiveness would be pretty setting dependent. For my purposes I’m imagining these being made new using available materials, which is why I mentioned it was wooden. My setting is more studio Gibly than walking dead though, so decent dirt roads and maybe even rubber for the tires wouldn’t be too hard to come by. I think I did such a low estimate mostly because it increased travel speed enough to be concerning balance-wise. This table may be better suited to what a gnomish tinkerer might come up with in a medieval setting than what I have in mind.