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