This study reviews the assumption that the lightweight design of commercial vehicles is significant from the aspect of the anticipated fuel consumption and environmental regulations that are consequently applicable to those vehicles. Generally speaking, it is noted that among the numerous trailer components, a stub axle, which is designed to independently operate as an integral part of trailer’s suspension, can play an important role in increasing the shipping capacity of a box trailer. For this reason, because each stub axle is comparatively a heavy unit in itself, and a total of six stub axles are mounted in a box trailer, the lightweight design of a stub-axle is noted as an essential factor to reduce the whole weight of a trailer. For a finite element analysis, an original CAD model is modified through removing a chamber, airbag, axle drum, bearing and pivot on a vehicle. In addition, the loading conditions are imposed considering three extreme driving conditions and the effects are studied when in the event of review of a fully loaded in a box trailer. A topology optimization is conducted to determine a lightweight design for minimizing compliance under these boundary conditions.