The Shimano Front Freewheel (FFS) was a proprietary bicycle drivetrain design of the 1970s that placed a freewheel between the pedal cranks and the front chainrings — enabling the rider to shift gears while coasting.[1] FFS rear freewheel is different than a standard freewheel because it's "stiff" with more friction than a normal rear freewheel. It will slip if necessary however, to stop the chain in the event of, for example, a clothing tangle — which could otherwise lead to injuries of the leg by the drivetrain, crashing of the bicycle, or both. *text from wikipedia