Reducing vehicle fuel consumption has become one of the most important issues in recent years in connection with environmental concerns such as global warming. Therefore, in the vehicle development process, attention has been focused on reducing aerodynamic drag as a way of improving fuel economy. When considering environmental issues, the development of vehicle aerodynamics must take into account real-world driving conditions. A crosswind is one of the representative conditions. It is well known that drag changes in a crosswind compared with a condition without a crosswind, and that the change depends on the vehicle shape. It is generally considered that the influence of a crosswind is relatively small since drag accounts for a small proportion of the total running resistance. However, for electric vehicles, the energy loss of the drive train is smaller than that of an internal combustion engine (ICE) vehicle. Therefore, drag represents a relatively larger proportion of the total running resistance. That makes it necessary to consider the influence of a crosswind in order to reduce electric power consumption in real-world driving. In this study, representative test conditions taking into account a crosswind were proposed for wind tunnel tests based on an analysis of U.S. market data such as vehicle speeds and wind speeds. The test results made clear the mechanism causing drag to change under the representative test conditions. The representative test conditions were calculated by the Monte Carlo method using real-world driving data. It was found that a yaw angle of 4 degrees is the most influential yaw angle. The mechanism causing drag to change was studied in wind tunnel tests. The factors affecting the change in drag were identified, and measures for reducing that change were examined.