Kings Springs exclusively use high quality, high stress X5K spring steel.This new generation steel allows King Springs to further improve many of their existing designs by reducing the amount of steel required in a spring, making it substantially lighter (by approximately 30%) and reducing the solid height therefore increasing travel. Being of particular benefit at all top levels of Motorsport, this new high stress material was introduced to the leading v8 super car teams (inc DJR/TP, FTR & NISSAN) in early 2007 giving a hugely successful endorsement of its characteristics & proven durability.Although considerably expensive, King Springs have introduced this new high stress steel to their passenger car and 4wd designs which benefit the most at no extra cost to the consumer. As of now all King Springs manufactured coils are now in X5K material.