Different tire sizes and components in some of the clutch kits for 2016 Polaris RZR models have different requirements. In some kits, like the RZR S 1000, you can convert your clutch kit to another application with a different secondary spring. The instructions may call for a particular set up using this spring when using different tires or conditions.
Springs are part of a complete tuning package, and the required spring is dependent on the rest of the tuning components used.