A new mass optimum design theory has been developed. The theory will deal with any shape of suspension coil spring and a non-linear spring rate (stiffness). This new theory is primarily based on the application of the finite element theory and the incremental method, and results in the mass optimal geometry of the coil spring.The pitch effect on the mechanical behavior of coil springs was also included. i.e. Both the torsion and the bending of coil spring elements were considered in the evaluation of the spring rate for the coil spring.Available manufacturing limitations have been incorporated as the constraint conditions in the optimum design phase. Examples are the spring bar diameter, the bar taper tolerance, and the spring coil radius, etc. The constraints for the allowable stress and the available spacing are also entered into this new theory.The verification of the product for this mass optimal design has been done by both the non-linear analytical computer code, ABAQUS, and the experimental testing at the GM Livonia plant. The results show excellent agreement of the design input, the ABAQUS analysis, and the experimental testing of the spring rate.