A link mechanism is placed between the rear arm and the cushioning unit, which functions on the lever principle with a variable factor that changes the lever ratio as it functions. When the shock absorber is close to the full extension of its stroke, as in normal riding on smooth roads, the lever ratio is large and the resulting ride is softer. As seen I the diagram, when the rear wheel moves from A to B, the stroke of the shock unit is shorter (A to B). But when the stroke of the rear wheel gets bigger (B to C), the lever ratio gets smaller and the spring rate gets stronger. In this way, this suspension can provide both a soft, comfortable ride and outstanding shock absorbing performance at times of high load.