PURPOSE: To provide a suspension coil spring of a small size for a knee-action type suspension system by interposing rotational kinematic pair means between opposite terminal ends of the suspension coil spring and respective means for supporting the opposite ends of the coil spring to remove bending moment acting on the coil spring.

CONSTITUTION: An arm 3 has a base end thereof pivotally mounted as at 5 on a chassis 7 and has the opposite end thereof supporting a wheel 6 by means of a pin 4. The arm 3 is supported adjacent to the opposite end thereof on the chassis 7 by means of a suspension coil spring 1. The coil spring 1 has each terminal end thereof fittedly engaged with a cylindrical spring seat member 8 which has a pair of rounded pins 9 integrally formed to extend in opposite diametrical directions from the center of an outer periphery of a cylindrical body thereof. At each of those portions of the chassis 7 and the arm 3 which support opposite ends of the coil spring 1 thereon, a supporting projection 10 is fixed which has a supporting groove 10' formed therein in which the pins 9 are loosely fitted. The coil spring 1 is thus supported at both ends thereof on these supporting projections 10 which act as a rotational kinematic pair means.