T he use of nodular cast iron is making a comeback with the discovery of TWC (thin wall casting) technology. The application of thin wall casting method in ductile iron will produce TWDI (thin wall ductile iron) material. The manufacture of thin wall ductile iron material opens up opportunities to compete with aluminum because of its mechanical properties and production costs are cheaper and the manufacturing process is relatively easy. The automotive industry is required to produce products with low fuel emissions and fuel-efficient vehicles. In this study, thinning of Vespa PX150 connecting rod components was carried out in the I beam section to reduce component weight. The manufacturing process carried out is the manufacture of casting designs and design simulations. The analysis process carried out, namely the comparison of the results of the Inspire Casting simulation analysis and the defects resulting from the simulation process. The Inspire Casting simulation shows that it is possible to make a connecting rod component by making a cavity in the I beam section. The connecting rod casting design functions properly without any suspicion of shrinkage defects of the removed parts in the I beam section. The prototype results obtained are similar to the Inspire Casting simulation results, where no casting defects occur in the piston rod component or workpiece.