It would be hard not to notice that Japan's streets are jammed with fixed-gear bikes. As reported here in December, these are simple, stripped-down bikes originally built for racing around velodromes; the single gear is locked to the back wheel, so the pedals keep turning when the bike is moving. But while these machines may be minimalist at their core, having just one gear, the youths who started this craze are finding ways to take it to the extreme.

Not content with getting from A to B in utilitarian fashion, these cyclists are turning the streets into a vast, ongoing spinoff of MTV's popular car restoration show "Pimp My Ride." Spend half an hour in Tokyo's Shibuya, Osaka's Minami Horie or Sanjo Street in Kyoto and it is hard not to do a double-take on cool kids riding fixed-gear bikes as carefully assembled as their outfits — from glaring all-white to riotous fluoro or black. And the weird and wildly colorful takes on this virtually maintenance-free cycle that are popping up like so many hallucinations are fueling a cottage industry for customizers.

Yo Kishiguchi, an Osaka-based designer who offers new types of frames built to suit every type of rider and every wardrobe, explains that behind the bespoke bike trend is an entirely new breed of bicyclist.