Our latest step forward in chassis tuning and control - the Progressive Bump Spring kit allows you to create and tune a progressive rate bump spring assembly. The outer spring is approximately 3/4" longer than the inner spring which allows for the car to feel the rate of the outer spring only for the first 3/4" of travel until it engages the inner spring at which time the combined rate of the inner and outer springs are what the car feels creating a progressive feel in the seat. This allows for the use of a soft outer spring than normal with the support of the inner spring to keep the car from over traveling. The inner springs are color coded the same as the outer springs - the same color is the same rate no matter if it's an outer spring or an inner spring - White-150 Yellow-200 Orange-250 Blue-300 Purple-350 Black-400 Red-500
Inner spring are currently produced in rates of Yellow-200 Blue-300 Black-400 Red-500
For example if you choose a Yellow (200#) outer and a Blue (300#) inner the car will have a 200# rate bump spring for the first 3/4" of travel and then it will have a 500# rate with both springs engaged. This system has been used with much success since it's introduction in early 2018.
SPECIFY SHAFT SIZE WHEN ORDERING - 1/2 - 9/16 - 5/8 **NOTE 500# INNER SPRING WILL NOT FIT OVER 5/8 SHAFTS SO YOU WILL RECEIVE AN EXTRA 400# SPRING IN YOUR KIT INSTEAD**