XB4 Spring Sets New optional progressive and linear springs Laser engraved for easy identification. Sold as a pair Individually measured controlled inspected and matched to provide identical damping characteristics Perfect spring match-ups Gives your car predictability and consistency The springs have been specifically designed to complement the big bore shocks. Set of 2. The spring rate of the linear springs is constant during the entire spring compression. The main advantage and benefit of progressive springs is that as the car initially enters the corner they work like soft springs to provide maximum traction. At the same time when the chassis begins to roll in the middle of the corner the spring rate progressively increases until they work like a hard springs which allows the car to maintain maximum cornering speed. Like all the other XRAY springs these springs are manually measured selected and matched into pairs to guarantee precisely equal length and damping characteristics. #368174 Front Spring Set Progressive - 2 Stripes (2) #368184 Front Spring Set - 2 Dots (2) - Standard #368185 Front Spring Set - 3 Dots (2) #368273 Rear Spring Set Progressive - 2 Stripes (2) #368284 Rear Spring Set - 1 Dot (2) #368285 Rear Spring Set - 2 Dots (2) - Standard #368286 Rear Spring Set - 3 Dots (2).