if you live in an urban area, chances are you've seen quite a few young people (with jeans that are probably too tight) riding around on bicycles that look like an incomplete 1970s schwinn hobby project cobbled together for emergency transportation only. Actually, they're supposed to look like that.
These bikes aren't new, though their popularity has exploded as of late. What you're looking at is a fixed-gear bike, commonly known as a "fixie." what sets these bikes apart from their more familiar cousins is that these are stripped down to the most basic of elements: Wheels, pedals, handlebars, a seat, and a frame. That's about it.
Popular with bike messengers for years, these zen-like modes of transportation hark back to the earliest bikes that were direct-pedal driven. One size fits all without any shifting or any coasting. If the wheels are moving, the pedals are moving.