How do scooter variators work?

Written by eileen faust
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How do scooter variators work?
Scooters in the U.S. have variators that control their speed. (hotwheels image by Robert Kelly from

The variator, or constant variable transmission, in your scooter helps your engine switch gears so you don't need to use a clutch. Many scooter owners change their variators under the impression it will improve their top speed, or to help their transmission more smoothly and quickly switch between gears, allowing for quicker acceleration.

The Parts

A variator is composed of two pulleys: a drive pulley that connects to the driven pulley by a belt. The drive pulley connects to the engine and the driven pulley connects to the clutch.

The Drive Pulley

The drive pulley is made of a front and back angled plate on a metal shaft with a belt sitting in between the plates. Inside the front plate on the drive pulley are two weights called roller weights.

The Driven Pulley

The back pulley has two angled plates connected to a spring called the contra spring which is connected to the clutch. The contra spring forces the two plates together when the scooter is idle or not in use.

Speeding Up

The plates of the drive pulley spin faster as the engine speed increases and the driveshaft speeds up. The roller weights in the drive pulley roll outward to the edge of the plate, forcing the front and back plates of the drive pulley together. This forces the belt toward the outer edge of the plates. The plates of the driven pulley are forced apart by the belt as the scooter speeds up, pushing the clutch and forcing the scooter into a higher gear.

Slowing Down

As the scooter slows down, the roller weights slide down toward the driveshaft, causing the angled plates to open up and the belt to drop down toward the centre. The contra spring's force then pushes the plates of the driven pulley back together, forcing the belt on the driven pulley outward toward the edge of the plates. This causes the clutch to slide into a lower gear, slowing the scooter's back wheel.

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