As bearings rotate, the raceways of the inner ring and outer ring make contact with the rolling elements. This results in a wear path on both the rolling elements and raceways. Running traces are useful, because they indicate the load conditions. They should be carefully observed when bearings are disassembled.
If the running traces are clearly defined, it is possible to determine whether the bearing is carrying a radial load, axial load or moment load. Additionally running traces can help determine the accuracy of bearing roundness, confirm whether unexpected loads or large mounting errors occurred, and shed light on probable causes of bearing damage.