The importance of light weight frames in automobiles is well known but becomes even more important in electric vehicles for direct gain it brings in range. Topology Optimization followed by Size/Gauge optimization very early in product life cycle serves as an effective method to determine the optimal material distribution path and tube sizing at the initial design phase itself so that the frame can be designed at an optimal level before heading to validation phase. It is usual practice to perform size optimization with 1D beam model. However, stresses due to geometric complexities including welds, and joints are not accurately predicted with the beam model and hence the optimization results are in a crude state. The method explored in this study explores using high fidelity durability model to perform size optimization which will increase the accuracy of the results.