A comprehensive analytical and numerical study on the design of passive, adjustable and automatic suspensions is presented. The fundamental limitations inherent in a passive system which are incompatible with the active and semi-active systems are demonstrated. The mathematical models of the vehicle are linear time-invariant lumped parameter systems with fixed configurations. The vibrations of the vehicles which are assumed to move forward at constant velocity are induced by deterministic ground roughness. With the above models the influence of active, semi-active damping on ride control is discussed. Computer simulation results of single-input-single-output (SISO) and multiple-input-multiple-output (MIMO) automobile models, show that the semi-active-damper (SAD) significantly improves the vibration isolation capabilities of today's vehicles, and consequently represents an attractive alternative for the automobile industry. When compared with fully active the SAD is distinguished by low power requirements and hardware simplicity. Feasibility design of an adjustable and semi-active hardware device capable of faithful and fast reproduction of a desired force is presented.