FASSTEK TORQUE SPRING

Function of the Torque Spring in CVT

In a scooter’s CVT (Continuously Variable Transmission), the torque spring (also called the contra spring or secondary spring) is located in the clutch assembly on the rear pulley.

Its main functions are:

1. Pulley tension control → It keeps pressure on the rear pulley (driven pulley), resisting the belt from moving to its highest gear too quickly.

2. Backshift response → It helps the CVT downshift quickly when the load increases (like going uphill or accelerating hard).

3. Balancing force → It works against the variator’s roller weights, influencing the timing of upshifting and downshifting.

Stock 1000 RPM vs. 1200 or 1500 RPM Torque Spring

A “1000 rpm” or “1500 rpm” rating refers to how stiff the spring is (higher number = stiffer spring).

A 1500 rpm torque spring is stiffer than the 1000 rpm stock spring.

Effects of installing 1500 rpm instead of 1000 rpm:

1. Later upshift (higher revs before CVT shifts)

The stiffer spring resists the pulley from opening too soon → engine stays at higher RPM longer before upshifting.

This gives better acceleration, especially at low speeds or on hills.

2. Faster downshift (better backshift response)

When you let off the throttle or climb a hill, the CVT downshifts more quickly, keeping the scooter in the power band.

 Switching from 1000 rpm (stock) to 1500 rpm spring will give you snappier acceleration and better hill climbing, but may cost you top speed, mileage, and belt life if not tuned properly (usually paired with adjusting roller weights).