Purpose: To conduct comprehensive experimental studies on the fatigue strength of side bearing springs for freight bogies, evaluating the effectiveness of thermal and shot peening treatments during their manufacturing process. Methods: The method of stand endurance (fatigue) testing of constant contact side bearing springs has been applied, allowing for obtaining endurance characteristics of actual components. Metallographic studies of spring steel have been conducted to investigate the influence of strengthening operations during spring manufacturing on their fatigue strength, with the assessment of mechanical characteristics of surface layers in various zones of the helical spatial beam. Results: Experimental force characteristics of spring sets for side bearings of an innovative freight bogie with a load of 25 tons (245 kN) on the axle have been obtained. Fatigue curves of the springs have been presented in a probabilistic aspect, enabling the determination of load factor for fatigue strength of the springs considering operational loading, as well as justifying the compliance of the spring sets with the regulatory requirements. Practical significance: Based on the research results, the considered constructive-technological variant of the constant contact side bearing spring for the freight bogie has been put into serial production. The test results allow us to reasonably determine the warranty mileage of the responsible assembly of the bogie and to conduct further work on the design modernization with the aim of increasing operational life.