SUSPENSION SYSTEM AND HELICAL COMPRESSION SPRING FOR THE SAME

PROBLEM TO BE SOLVED: To provide a knee action-type suspension system in which the stress of a helical compression spring for the suspension system can be brought close to an equalized condition.SOLUTION: A knee action-type suspension system 11 includes: an arm member 20 freely swingably supported in the vertical direction around a pivot 31 provided at an arm mounting part 30 of a vehicle body; a helical compression spring 21 disposed between a lower spring seat 22 and an upper spring seat 23; and a shock absorber, etc. The helical compression spring 21 expands and contracts between a full rebound state (maximum stretched state) and a full bumped state (maximum compression state) according to the size of load applied to the vehicle body. Strand 40 of the helical compression spring 21 has large diameter strand part 40a provided at a pivot side portion 21a of the side near to the pivot 31, a small diameter strand part 40b provided at an anti-pivot side portion 21b of the side far-off from the pivot 31, and a wire diameter change part 40c.