Speed significantly impacts the stability of a loaded truck on curves with suboptimal geometric design. This study examines how truck geometry and loading conditions affect speed changes on horizontal curves in rural highways. It uses the IPG Truckmaker simulation tool to model vehicle dynamics, with accuracy verified through field tests. Key findings include the distance before a curve where a truck begins to decelerate and the point of maximum speed reduction when traveling at 65 km/h on a straight road. Results reveal that curves with radii <100 m are particularly problematic, showing high-speed reductions before and after the curve. The study’s insights can guide highway engineers in placing caution and speed limit signs on curves frequented by trucks and identifying areas needing corrective measures. Understanding maximum speed reduction aids in evaluating curve consistency and underscores the need for adequate curve radii on rural highways.