Originally Posted by invisiblehand
Very true. Just to be clear, my concern is not whether one could reach those speeds but whether it would be wise to reach those speeds on typical city roads on a short wheelbase sub-20" wheel folder.
BTW, there are people who share my opinion as well as people who believe that I overestimate the likelihood of a mishap. So I would take my opinion with a grain of salt.
After riding around on 8" wheels I'm starting to think that the wheelbase is probably more important than the wheel size.
At speed, I think the momentum of the bike will carry the wheel over holes which are bigger than the wheel itself. Of course, when you get air you lose stability, but as long as the wheels are far enough apart only one wheel will get air at a time, while the other remains stable (increasing the overall stability of the bike).
I wonder how much this actually changes for a bike with larger wheels. After all the contact patch is still small and as long as the contact patch is going over the hole instead of in it, the rest of the wheel doesn't matter (it isn't touching anything). Of course, there's the inertia of the wheel to keep it pointing forward, but that's related to the wheel weight rather than the wheel size and the wide wheels/tires commonly used on smaller wheels make them just as heavy as their larger brethren.
Remember that car tires are even smaller in diameter and just about pothole sized (probably no coincidence), yet they remain stable due to wheelbase and tire width.