A dual-mass piezoelectric bar harvester is developed for energy harvesting from ambient vibrations of a vehicle suspension system subjected to roughness of road surfaces. The harvester is made of a sprung mass (body mass) and an unsprung mass (wheel mass) connected by a piezoelectric bar transducer which is equivalently modeled as a suspension spring and a damper in a mathematics model. The dual-mass piezoelectric bar harvester is practically designed in a vehicle suspension system on wheels to generate an electric charge. To describe the energy harvesting process, a mathematics model is developed to calculate the output charge and voltage from the harvester by an iteration method in the temporal domain. The influences of some practical considerations, such as the width of the piezoelectric bar, the speed of vehicles, and the class of the road roughness, on the root mean square of the generated electric power are discussed. Our results show that a power up to 738 W can be realized for a practical design of the harvester with a width and height of the piezoelectric bar of 0.015 m and 0.1 m respectively. This research develops a new design method for efficient and practical energy harvesting from vehicle vibrations. (C) 2015 Elsevier Ltd. All rights reserved.