This paper aims to investigate the impact of vehicle velocity on the rollover stability of a fully loaded tractor semi-trailer during lane changes and turning. Specifically, the study focuses on velocities ranging from 30 km/h to 60 km/h. The investigation found that vehicle velocity is a critical parameter that can affect the potential for rollover during lane changes or turning. The results showed that to ensure the vehicle moves steadily and does not roll over during these maneuvers, the steering angle must be controlled and kept within certain limits. The study provided specific recommendations for maximum steering angles at different velocities. For instance, to ensure stability when the vehicle is moving at 60 km/h, the maximum steering angle should be less than 4 degrees. Similarly, at 50 km/h, the maximum steering angle is recommended to be less than 6 degrees, and at 44 km/h, it should be less than 8 degrees. At lower speeds, the recommended maximum steering angle increases, with the maximum recommended angle at 36 km/h being 12 degrees. These findings highlight the importance of carefully controlling vehicle velocity and steering angle to minimize the risk of rollover accidents. By providing specific recommendations for different velocities, this study can inform the design and safety testing of vehicles to improve their stability and safety during lane changes and turning.