The study presents investigation is the pneumatic spring suspension system of diesel train DPKr-3. The research aims to estimate the influence of track irregularities on the pneumatic spring dynamic stiffness and its damping coefficient at 170–250 km/h speeds. The pneumatic spring suspension system characteristics were studied using an improved mathematical model of the system ‘rolling stock-track’. The pneumatic spring ‘force-strain’ relations are obtained at different values of the connecting pipeline diameter and length at high speeds. It was determined that increasing a connecting pipeline diameter from 20 to 40 mm and a speed change from 170 to 250 km/h causes decreasing a spring dynamic stiffness. It is shown that at a speed range from 170 to 250 km/h and a connecting pipeline diameter from 20 to 40 mm, a change in a pipeline length from 3 to 6 m does not lead to significant changes in stiffness. It was found that in the range of speeds from 170 to 250 km/h, the damping coefficient has maximum values with a diameter of the connecting pipeline from 25 to 30 mm.