Active suspension is a type of automotive suspension that controls the vertical movement of the wheels relative to the chassis or vehicle body with an onboard system, rather than in passive suspensions where the movement is being determined entirely by the road surface; see Skyhook theory.Active suspensions can be generally divided into two main classes: pure active suspensions, and adaptive and semi-active suspensions. While adaptive suspensions only vary shock absorber firmness to match changing road or dynamic conditions, active suspensions use some type of actuator to literally raise and lower the chassis independently at each wheel.