Abstract: The rolling contact mechanics in a simple flat belt drive has been experimentally studied to explore the mechanism of relative displacement and friction generated at the belt/pulley interface in both the driver and driven cases. We have found that under the slow speed considered, no sliding takes place at the belt/pulley interface, and that relative displacement between the elastomeric belt and the pulley is achieved by means of cyclic detachment. This calls into question the universal validity of the sliding-based approach to analysis of the belt drive contact. Stick-slip instabilities are observed in both the driver and driven pulleys, though the scale of these events is much larger in the first case, which renders the driver pulley as the main source of noise and vibration. The rolling contact mechanics is different in the driver and driven pulleys, which results in much different slip arc angles and calls into question the validity of the symmetric approach to analysis of the belt drive contact. Schallamach waves of detachment are observed in the driver pulley, while in the case of the driven pulley, the system instabilities result from the combination of the pulley rotation and the adhesion hysteresis.