In this paper the relationship between weight reduction and fuel economy is determined. This is executed with simulations for the three different propulsion systems ICE (internal combustion engine), hybrid system and fuel cell (FC) system. Furthermore, the three different vehicles classes compact, mid-size and SUV are considered along with two driving cycles, NEDC and HYZEM. The re-sizing of the propulsion systems according to the lighter vehicle weight to achieve the same acceleration as the basis vehicle is implemented as well.As an overall result it is established that no general value for the fuel consumption reduction per weight reduction exists. It is very important to consider all boundary conditions, especially the used driving cycle, the examined vehicle class, the type of propulsion system and a possible powertrain re-sizing. In detail the results show values between 2 and 8 % fuel consumption reduction at a 10 % weight reduction. Conventional powertrains fall in a range of 2 to 6 % fuel consumption reduction for all driving cycles and vehicle classes. A strong impact of the powertrain re-sizing on the fuel consumption reduction is detected for the conventional powertrains, especially in the NEDC driving cycle. For the alternative powertrains the re-sizing has less impact.