it uses the centripical force, the greater the rpms, the more centriphical force there is. the bearings you see sit on a angled "ramp" towards the outside of the clutch. as rpms increase, so does centripical force, therefore throwing the bearings out farther harder, therefore pushing in on the clutch plates harder, and allowing the clutch to hold more horsepower. i have ran one on my built raptor for several years. works well, and a cost effective alternative to the pricey direct drive units.