Cargo loaded on vehicles is easily made unstable during turning or braking because of the high position of the center of gravity. In Japan, many rollover accidents of large-sized cargo vehicles occur to this day. To prevent these accidents, we are studying the behavior of cargo vehicles during rollover by conducting tests that include the steady state circular test, lane change test and J turn test in order to study the mechanism of rollover and its boundaries. We are studying a method to simulate rollover phenomena and a method for tests to verify rollover performance.