Categories could be:
-tech (how-to's on setting up engines, brakes, jackshafts and gearing, basic tips for frame construction, things like that)
-A-Z listing of bike brands (Asuza, Cat, Zebra, and so on). Instead of each bike having its own sub-category, each brand starting with the letter A, then B, then C ... kinda like minidoodle has it. You may also want to consider a "Miscellaneous Builds" category for those of us who have built bikes from scratch and not an existing frame or kit.