Technology Digests / Wheel-Rail Interaction Affecting Hunting Stability

TD24-022

June 25, 2025
Authors
  • Ulrich Spangenberg
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Key Findings

  • The equivalent conicity at 3 mm (0.12 inch) lateral amplitude, while suitable to indicate hunting, is not an accurate measure to quantify the hunting threshold speeds of North American freight wheels.
  • Rail profiles with smaller crown radii resulting in gage shoulder relief are less prone to hunting occurrences.
  • An approximately constant cone (flat) equivalent conicity function may contribute to loaded car hunting.
  • When worn wheels are considered, especially in the loaded condition, the lateral acceleration criterion may erroneously identify hunting occurrences more frequently than the lateral displacement criterion.
  • *NUCARS(R) is a registered trademark of MxV Rail

Wheel-Rail Interaction Affecting Hunting Stability

Under the Association of American Railroads (AAR) Strategic Research Initiative (SRI) program, MxV Rail engineers performed NUCARS(R)* simulations to determine the characteristics of interacting wheel and rail profiles that may contribute to severe hunting instabilities in railcars. Historically, wheel profile coning has been used to allow wheelsets to 1) find an equilibrium rolling position, 2) remain centered on tangent track, and 3) better negotiate curves resulting in reduced flange wear and rail side wear. Unfortunately, coning of the wheel profiles is often accompanied by undesired instability on tangent track known as hunting. Minor instability on tangent track is usually acceptable, but extreme instability can damage lading, cars and/or tracks, and can potentially result in a derailment. The increasing use of wayside wheel profile detectors allows analyses such as the one described in this Technology Digest to be implemented more successfully; thereby proactively optimizing safety and efficiency of the network. For…