is stiff or poorly steering or axle sets that don't follow the path of the track correctly. presents itself like 'dog tracking" where the trucks are biased to run against the flange on one side or the other. truck performance defects include tracking position and angle of attack on a per-axle basis, as well as rotation, shift, inter-axle misalignment, and tracking error on a per-bogie basis. truck performance detectors can provide early detection of bogie defects, and early warning of derailment risks through flange climb or rail break.