I gleaned this from Scooter Therapy... "
http://www.scootertherapy.com"
Mopeds and scooters have a couple of different transmission types used. The top speed is determined by how fast the engine can spin, and what the gear ratio from the engine to the wheel is. You need power to get started, (low ratio) and high top speed (high gear ratio) How is this achieved? Several ways, depends on your machine, as to how fast it is intended to go.
One is a manual gearbox, like a motorcycle, where you clutch with your hand and shift gears manually. Another is automatic clutch and manual shift, where you shift gears with your foot but the clutch action is automatic. A very common style for mopeds is a single speed automatic with a centrifugal clutch. This type requires no shifting or manual clutch operation, and top speed of the moped is determined by how fast the engine can spin after the centrifugal clutch is fully engaged. (not slipping).
A better way is with pulleys and a drive belt, where the pulleys have movable sides so when the pulley halves come together, the belt moves higher in the pulley, increasing the diameter of the pulley and changing the gear ratio. As the belt moves up in the front drive pulley, the halves of the rear pulley are moving apart and the belt is sliding down. This makes the rear pulley smaller, further increasing the gear ratio to the rear wheel. The top speed of this type system is determined by the ratio produced when the front pulley is fully compressed and the rear pulley is fully apart, offering the highest ratio available without making the pulleys a different diameter or replacing the gears in the rear gear box with a different size. This type of system uses roller weights to force the front pulley together, and a spring to keep the rear pulley from coming together too easily.
Changing the weight of the rollers will alter the speed at which the engine spins, until the clutch is fully compressed. The rollers weights are telling the pulleys when to shift up to the next ratio. Changing them does not affect top speed at all, just how long it takes to get there. The rear gear box transfers power from the rear pulley to the wheel, commonly with two shafts and two gears. Changing the size of the gears will affect the overall ratio, having nothing to do with the belts or pulleys. Although it will affect them, in that more power is needed to pull a higher ratio.
peace
