SS and G6 discs are Sprung Centered for noise reduction on solid ACT Flywheel. Must use ACT Flywheel with Sprung Hub Discs for proper clearance. (Flywheel not included) XT/Race Sprung 6 Pad Moderate to heavy pedal effort, aggressive engagement, OE to mild gear rattle; Moderate friction life, extended by ACT's exclusive diaphragm design; Carefully engineered, precisely assembled, accurately balanced, uses select ceramic friction materials for high heat tolerance and maximum performance; Recommended for high horsepower street or race use; 100% clamp load tested and dynamically computer balanced for smooth high RPM reliability TS4-XTG6 kit features an Xtreme pressure plate for the most demanding driver. ACT Xtreme pressure plates use exclusive diaphragm design to increase clamp load, reduce deflection and maximize clutch life. All diaphragms endure a four-stage, heat-treating process for unparalleled performance. ACT pressure plates have precision cover stampings to provide rigidity and consistency. ACT's 6-pad spring-centered race disc features a spring-center construction to properly damp torsional vibrations and resist failure under harsh conditions. ACT spring retainers utilize wraparound spring windows and thicker retainer stampings to provide spring support, reduce stress concentrations, and increase strength and reliability. With the 6-pad spring-centered race disc, engagement is harsher, but shifting is faster. The 6-pad spring-centered disc is recommended for larger clutch sizes to absorb more heat.