Vehicles that are capable of driving on and off paved or gravel surface are referred to as off-road vehicles. In general, these vehicles are characterized by having large tyres with deep, open treads and a flexible suspension, or even caterpillar tracks. Other types of vehicles that do not travel on public streets or highways are generally referred to as off-highway vehicles, which would include cranes, tractors, bulldozers, backhoes and forklifts (Faris et al, 2009a; http://en.wikipedia.org/wiki/Off-road_vehicle).

Unlike a road vehicle, an off-road vehicle is subjected to ride vibrations of low frequency and large amplitude, which cause bodily discomfort to the operator, and limit the mobility and performance of the vehicle (Srivinasa et al., 2003). Generally, the speed of off-road vehicles over rough terrain is determined by the ride quality not by the engine power. For this reason, researches are currently being undertaken to improve the ride dynamics of these vehicles using an advanced suspension system.