Street trackers are just dirt track-looking bikes made street legal. Mostly they have smaller tanks and wide bars.
I think of street fighters as bikes that are parked outside. Made from dissimilar parts, perhaps even other brands. They are made to be used and abused, but may be sleepers, too. I get the impression that a vague notion of that concept has been elevated (just as many styles originate in the lowly city streets), made new, and merchandised. My concept is one of utility with an overtone of "badboy" in the way that outlaws have always been romanticized.
I see bobbers as originally being modified for speed on a budget. It's a post-war idea of throwing away easy weight- like fenders and covers. Maybe a little engine work. Bobbers sort of became choppers and now bobbers (derived from the idea of "blunt -or even rudely- cut". Many women wore a hairstyle called a bob that was just made to look as if it was just quickly cut). I think "bobber" is an American term, whereas "cafe" is English.
I think street fighters and cafes were more closely related because English guys were more willing to interchange parts- like putting different engines in a featherbed frame. Americans have too much brand loyalty to do that kind of thing.
No real copper in $.02 anymore...
