Electric vehicles are equipped with electric-drive wheel systems, so the development of matching hub reducers with proper durability is important. Based on the Shanghai standard road-driving cycle, this paper forecasts the load spectrum for key components of the hub-reducer system. After considering the material strengthening under low-amplitude loads, the reducer system running-in test specification is issued. This paper also develops an electric-drive system durability test specification on the basis of the Miner linear cumulative damage theory, and estimates the hub-reducer durability mileage. The bench test for durability shows that the first round of the prototype design satisfied the durability mileage required, and the bending-fatigue strength of the gear is sufficiently reliable, which gives possibilities for further lightweight designs. This method can be applied for the lightweight designing of other key automotive components. It also provides empirical evidence for developing automotive products that meet the standard road-driving-cycle conditions.