French Variated bikes have a short belt which drives the chain which drives the wheel. when the the variator moves so does the engine to account for the changing pulley size. Counter clutch bikes account for this without the engine needing to move. On a vespa the clutch is mounted on the rear wheel (no chain) and the pulley behind it has a spring in it. as the front variator pushes the belt outward it pulls the belt inward in the rear (duel variation) this has the affect of making a more significant "gear change" as you go up and down through the revs. so when the front is big the back is small (top speed) and when the front is small the back is big (hill climb) its the best of both worlds! Ciao For the win!