Synchronous belts have a tendency to incur belt climbing, whereby the belt pitch circle does not coincide with the pulley pitch circle at the beginning of meshing and at the end of meshing due to the belt bending rigidity and interference between the belt and pulley teeth. The present study experimentally and theoretically investigates the transmission error having a period of one pitch in synchronous belt drives under quasi-static conditions and the transmission force when a belt having a curvilinear tooth profile incurs belt climbing. For a constant transmission force, belt climbing increases when the installation tension decreases, and is particularly large on the slack side when the installation tension is below a certain tension. Belt climbing is slight at the end of meshing on the driven pulley. Experimental results obtained for the transmission error agree closely with the results computed using the measurement results of belt climbing. The greatest reduction in transmission error is obtained when the installation tension is set such that the rate of decrease in belt climbing on the slack side with respect to installation tension becomes small.