This paper presents a multidisciplinary design optimization of the rear leaf spring for a Dayun truck, aiming to simultaneously enhance mechanical performance, reliability, and ride comfort. The research methodology integrates analytical calculations, advanced numerical simulations, and systematic experimental tests. A detailed parametric model, incorporating all geometric details and the material properties of 55Cr3 alloy steel, was developed in SolidWorks software. This model was subsequently imported into ANSYS software for comprehensive finite element analysis (FEA), including nonlinear contact simulation between layers, stress distribution assessment under combined loading, and fatigue life prediction. Experimental validation involved fatigue tests conducted in accordance with ASTM standards and spring rate evaluation using a RANJBAR QCS98 testing machine. Statistical analysis of the results in Minitab software demonstrated that the implemented thickness modifications, while maintaining the spring rate within the desired specification (standard deviation < 2%), yielded a significant 18.5% improvement in fatigue life and 12.3% reduction in maximum stress. These performance enhancements achieved with only a marginal production cost increase of less than 4%, confirming the economic viability and practical feasibility of the optimized design.