A vehicle comprises a frame, a slide rail, and front and rear arms pivotally coupled to the frame and the slide rail. Front and rear shock absorbers are interposed between the slide rail and the frame. A linkage system is coupled with the slide rail, the front arm, and at least one shock absorber. The vehicle suspension system becomes increasingly stiffer as the deflection of the slide rail increases, to contribute to a more comfortable ride and to reduce the risk of bottoming-out.