After a decade of commuting and travelling by bike, I just learned about balance bikes. I get the sense that this is a fairly well-known technology, but for those like me who are just hearing of it today, I'll explain. A balance bike has no pedals, but the seat is low enough for the rider's feet to touch the ground. Thus the rider propels the bike essentially by running on the ground. But just like on a regular bike, the rider can coast, allowing forward progress to continue without constant exertion.
Balance bikes appear to be used almost exclusively as a training tool for little kids who can't balance on a real bike yet, hence the name. (I didn't know what they were because as a kid I just had training wheels and then a regular bike. I guess I was precocious?) But I started wondering why I've never seen an adult riding one. One clear problem with the pedal-less design is that it can't support multiple gears, so there is no way to leverage mechanical disadvantage to achieve higher top speeds. But that can't be a total dealbreaker--first of all, not everyone is out there trying to keep up with motorized traffic. Also, there is a contingent of talented riders who enjoy single-speed fixies, so clearly some people don't mind not changing gears.
On the other hand, balance bikes seem to have clear benefits. In addition to ease of balance, they are no doubt less difficult to maintain, cheaper to produce, and safer to fall from. And yet I never see anyone riding a balance bike. What gives? Are grownups just self-conscious about being seen riding "kid" bikes? Or are there other serious drawbacks I haven't thought of? Are there examples of adults riding balance bikes that I don't know about?