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.

This paper presents the results of research on the vibration of the Hyundai Universe bus using an air suspension system and mechanical suspension system when it is run at different speeds on random road surface profiles according to ISO 8608:2016. The research results show that the used air suspension system ensures smooth movement and dynamic safety according to TCVN 6964:2008 (ISO 2631:2003) and VDI 2057:2017 standards. The maximum vehicle speeds on different road classes varied from 105km/h to 65km/h. A vehicle with an air suspension system provided a smaller root mean square of vibration acceleration RMS(Z) than a vehicle with a mechanical suspension system. The root means square of the wheel load RMS(Fz) of a vehicle with an air suspension system is about 99.6% of that of a vehicle with a mechanical suspension system.

The braking force of the tractor semi-trailer depends on many random factors and road parameters. Therefore, determining the braking force based on theoretical calculation or simulation is not accurate. This paper presents the method of setting up the braking force measurement system of the tractor semi-trailer on the road and constructing the braking dynamics model of the tractor semi-trailer to investigate the braking force using Matlab-Simulink software. The study results show that the average error between the simulation and experimental results of the tractor semi-trailer braking force is 9,81%.

Multi-purpose forest fire fighting vehicles should carry a set of firefighting equipment such as high-pressure water pumps, tree cutters to create a fire isolation corridor, vacuum, and blowing machine high-speed wind sandblasting devices etc. The bumpy road and velocity of moving vehicles can affect the vibration response of these vehicles. Hence, in this research the vibration analysis of a Multi-purpose forest fire fighting vehicle mounted on a URAL4320 active three-wheel drive vehicle is simulated and analyzed. The effect of road bumping and speed of vehicle on the vibration parameters are studied via building mathematical models with 19 degree of freedom for simulating the suspension system of the investigated vehicle.