How Wheel/Rail Profiles Affect Hunting Stability


MxV RAIL R&D, MAY 2026 ISSUE: The use of coned or profiled railway wheels can lead to instability at higher speed on tangent track, also known as hunting. Extreme hunting occurrences can cause damage to lading, cars and/or tracks and potentially result in derailment. MxV Rail engineers set out to determine the worn wheel and rail profile characteristics that can be used to judge the stability of a vehicle without requiring detailed simulations. Identifying these characteristics would allow for better profile design, maintenance planning, and maintenance execution.

The hunting performance of various wheel and rail profiles was studied by running simulations using both an “empty standard covered hopper” and a “loaded intermediate covered hopper,” per M-9761, on tangent track in NUCARS® (a registered trademark of the Transportation Technology Center, Inc. dba. MxV Rail).

The simulations used measured worn wheel profiles from 14 in-service railcars and the AAR KR wheel profile. Seven unique rail profile pairs were used for the hunting assessment, including tangent grinding profile templates employed by three different Class I railroads and measured profiles from the M-976 hunting test zone. The stability of each wheelset was simulated 14 times owing to different combinations of car and rail profiles. The track had no irregularities other than a single 0.25-inch lateral alignment perturbation over 50 feet near the beginning of the simulation to initiate hunting. In the simulations, the velocity of the car was reduced from 80 mph to 10 mph in 140 seconds to determine the critical, or hunting, speed for a given wheel-rail combination by evaluating the standard deviation of the lateral acceleration of the carbody and the oscillating lateral wheelset displacement relative to the center of the track.

Pearce (2) and Sawley et al. (3) have suggested that hollow worn wheels are more prone to hunting. Therefore, the average hollow wear within a truck was determined together with the number of times that the truck experienced repeat hunting occurrences. The maximum number of repeat hunting occurrences that were possible was 14. Figure 1(a) indicates there is no clear relationship between repeat hunting occurrences and the average hollow wear within the truck, but some wheel profiles repeat more than others. The research suggests that a characteristic of the wheel profile shape can make profiles more prone to hunting; however, that characteristic has yet to be identified, and therefore, it is not understood. Pearce (2) further stated that flattening the rail crown increases the equivalent conicity of the contacting pair, and it is generally accepted that such rail profiles will increase the likelihood of hunting. When evaluating the performance of the rail profiles, researchers found that hunting occurred more often on the measured “flattened” rail profiles and less often with an increased amount of relief on the gage shoulders of the rail profiles. The rail profile grinding templates plus a measured rail profile from the hunting test zone are overlaid in Figure 1(b).

Figure 1. Hunting repeat occurrences related to a) the wheel profile performance and b) the rail profile performance.

From these results, it was concluded that 1) there is a yet-to-be-understood characteristic of the wheel profile shape that drives the hunting performance, and 2) smaller rail crown radii that result in gage shoulder relief are less prone to repeated hunting occurrences.

The Technology Digest4 this article is based on can be found in the MxV Rail eLibrary along with more than 1,000 other publications describing the railway research, testing, and analysis available from the AAR SRI program. Explore www.mxvrail.com to learn more about MxV Rail and our research capabilities. 

References

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