This Polini compression spring increases the force by 34% over the original and is as a result ideal for tuning applications. The compression spring has the task of pressing the rear shifter pulley against the belt, so dictating how the Variator shifts. Replacement of the compression spring for a stronger one is therefore necessary if the power of the engine is increased by tuning, especially if the pulley begins to slip or the engine fails to stop. The Variator is very dependent on the compression spring, to the extent that the Vario always has to be adjusted when the spring is exchanged for another. Original spring strength: 65-70mm/kg. Polini spring strength: 65-94 mm/kg. Wire thickness 6.2mm. Overall length: 128mm. Internal diameter: 58mm.