This paper is concerned with the tank-to-wheel (TTW) analysis of a series plug-in hybrid_x000D_ electric bus operating in Gothenburg, Sweden. The bus line the powertrain model are described._x000D_ The definition the calculation method of the recuperation fuel-to-traction efficiencies are_x000D_ delineated for evaluating the TTW energy conversion. The two efficiencies are quantified and_x000D_ compared for two optimization-based energy management strategies, in which convex modeling and_x000D_ optimization are used. The impact of downsizing the battery on the two efficiencies is also investigated._x000D_