Weight reduction and material substitution are increasing trends in the automotive industry. In this project, the task of substituting the steel body side in the monocoque of a large SUV towards an aluminum body side was investigated through a design engineering approach adopting a breadth-first analysis method. One conclusion based on the analysis is that the choice of joining technology would become arbitrary due to the breadth-first approach. In this paper, the authors present their findings from the aforementioned case, including the challenges with switching between materials with fundamentally different properties when performing material substitution projects. The possibility of having taken a depth-first analysis approach, and the possible effects on the project result, is discussed.