In the past decade the applicability of belt-drives has been extended significantly due to their increased reliability. With automotive engines it is now common to join a large number of belt-drives into a single, long belt-drive with several tensioner pulleys. However, these belt-drives can exhibit complex dynamic behaviors, which can lead to undesirable noise and vibrations. The aim of this paper is to present an effective and realistic numerical model to predict the dynamic response of such belt-drives. Based on the simulated responses the belt-drive construction can then be optimized in order to increase efficiency, reduce noise and vibrations, etc. The belt-drive model is based on flexible multibody system dynamics, where the belt is modeled using beam elements. With the developed contact model between the belt and the pulley, we can accurately predict the contact forces and stick-slip zones between the belt and pulley. The identification of the belt-drive's material properties is based upon experimental data. Several original experiments are proposed in order to extract the damping and friction characteristics of multi-ribbed belts. Finally, the applicability of the belt-drive model is presented by simulating a serpentine belt-drive, considering non-steady belt-drive operational conditions, which are common in automotive engines.