Abstract The design of a suspension system emphasizes weight reduction in this high-computation technology era. Understanding that the reduction of suspension mass can lead to cost and material reduction is important; moreover, the riding performance of the vehicle should be improved. Topology and topography structure optimization for the spring lower seat is performed to reduce the weight of a passenger car spring lower seat design under stress and structure compliance constraints. Topology optimization is performed to identify the density of the required elements, whereas topography optimization is utilized to strengthen the structure of the lower seat by applying bead parameters in the model. Based on topology optimization, the mass of the model is improved by a reduction of 36.5%. Topography optimization is subsequently performed to fine-tune the topology-optimized model. Beads are added to the model to strengthen the stiffness of the structure. The topography-optimized model has successfully increased compliance by 27% compared with the sole topological optimized design. With the combination of topology and topography optimization techniques, the weight of coil spring lower seat has been successfully reduced while preserving the strength. Suitable sheet materials are proposed to match the optimized coil spring lower seat design.