Here's the thing -- the Sheen ARE their bikes. Literally. They're made of some kind of fluid chrome matrix that means they can remake themselves into anything they choose. And what they choose is to tear ass on two wheels.
The Sheen don't work with anyone -- hell, they don't communicate with anyone, either. They're robo-punk teens with attitude and no interest in organic life. Their entire existence is built around some deity they call "Jaimsdeen."