Abstract A fundamental theoretical study is performed for the computation of the expected fatigue damage of the main structures of a road vehicle running on a randomly profiled road. The expected fatigue damage can be estimated according to Miner's rule and Rain-Flow counting employing Rychlik method. Referring to a 2 d.o.f. mechanical system, the standard deviations of the random forces on acting on the body and on the wheel are computed symbolically by means of the Power Spectral Density Method. The influence on damage of vehicle parameters is discussed.