Purpose. This study aims to determine the geometric parameters of the brake pads of freight cars under hazardous wear. Methodology. A set of operational and theoretical studies concerning the occurrence of hazardous wear, which changes the geometric parameters of the useful contact area of the brake pads of freight cars at different established gaps between the pad and the wheel, which significantly impairs the effectiveness of train braking. Using the collected statistical material, computer mathematical modeling of the upper hazardous wear at different gaps was performed and the negative factors affecting the brake system were identified. MathCAD and AutoCAD software was used. Findings. As a result of inspections of the mechanical part of the brakes, attention was paid to the abnormal wear of the brake pads of the freight cars, which is formed by the fact that the common gravity center of the pad and the shoe, placed on the pendular suspension, do not coincide with the center of the hole in brake beam king post with any pads. In order to investigate possible causes of abnormal wear of the brake pads, their real images and theoretical schemes are given, which allow to establish the causes of the formation of abnormal wear of the pads at different gaps between the pad and the wheel and to determine their change of geometrical parameters that affect the useful contact area. When comparing the results of calculations according to the coordinate method performed in the MathCAD software environment and the graphic method (in AutoCAD), for determining the geometric parameters of the formation of the upper hazardous pad wear, depending on the regulatory pad wear between the wheel and the brake pad, it is theoretically proved that the error between them does not exceed 5–7%. Originality. For the first time, the principles of the methodology for determining the geometric parameters of the useful contact area of the pads with the formation of upper hazardous wear, depending on the gap between the wheel and the brake shoe, were formulated using coordinate and graphical methods. Practical value. It is advisable to apply the results of the research obtained in the work in the design and technological departments and bureaus when designing both mechanical brake systems for the undercarriage of innovative cars and for improvement of the cars currently operated at the railways.