The paper presents a method for the indoor testing of road vehicle suspension systems. A suspension is positioned on a rotating drum which is located in the Laboratory for the Safety of Transport at Politecnico di Milano. Special six-axis load cells have been designed and used for measuring the forces/moments acting at each suspension-chassis joints. The forces/moments, wheel accelerations, displacements are measured up to 100 Hz. Two different types of test can be performed. The tire/wheel unbalance effect on the suspension system behavior (Vibration and Harshness, VH) has been analyzed by testing the suspension system from zero to the vehicle maximum speed on a flat surface and by monitoring the forces transmitted to the chassis. In the second kind of test, the suspension system has been excited as the wheel passes over different cleats fixed on the drum. By analyzing the forces and the acceleration measured on the suspension system, a set of performance indexes has been derived from the analysis of the data both in time and frequency domain. A simple mathematical model of the tire/suspension system has been derived and validated to analyze the relative effect of the road irregularity and of the tire/wheel unbalance on an actual suspension dynamic behavior. It has been shown, that the direct measurement of the forces and moments at the suspension-chassis joints is an effective way for understanding the vibration and harshness suspension performances.