A scale model simulation is developed to study passenger car running performance. Emphasis is placed on a study of vehicle overturn according to drastic steering. Two model cars are used. They have suspensions, pneumatic tires, shockabsorbers and steer mechanism. As the tests are performed while coasting, they do not need the engine and drivetrain to test of the basic running characteristics, the model is continuously given the necessary speed by the rotational arm or by the full size cars. Especially, at J turn, they are shot by the catapult.