This paper investigates the emergency braking dynamics of the 2022 KIA Seltos using CarSim simulations to determine safe speed limits under different road-surface conditions. Simulations were conducted at speeds ranging from 60 to 120 km/h on dry asphalt, wet asphalt, and snow-covered roads. The results show that tire-road adhesion strongly affects braking performance. On dry roads, the vehicle achieves a deceleration of approximately -6.5 m/s²; however, the simulated braking distance at 120 km/h is approximately 110 m, exceeding the 100 m minimum safety distance specified in Circular No. 38/2024/TT-BGTVT when only the braking phase is considered. On wet roads, deceleration decreases to approximately -4.9 m/s², resulting in an average increase of about 26% in braking distance across the investigated speed range. Accordingly, the safe operating speed should be reduced to below 100 km/h. On snow-covered roads, deceleration is limited to approximately -1.96 m/s², and the braking distance becomes more than 220% longer than that on dry roads. Therefore, the recommended speed should not exceed 80 km/h. These results provide vehicle-specific simulation data and support adaptive speed regulation, infrastructure design, and braking safety assessment in Vietnam.