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Springs with low static deflection (stiffer springs for a given load) should have a more severe rig test than springs with a higher static deflection. It was theorized that the alternating to mean strain ratio increases as the spring stiffness for a given load increases. A series of strain measurements were conducted using three different spring stiffnesses for two different bogie load conditions. A total of six different static deflections were measured. The measurements at the truck bogie suspension show a clear trend that the ratio of alternating to mean strain increases as the static deflection decreases. Damage calculations were conducted to compare the relative fatigue damage caused by the road inputs. This data was then used to determine the alternating to mean strain ratio for a 100,000 cycle rig test equivalent to the relative damage caused by road inputs. It was found that the lower the static deflection, the larger this ratio must be.

Development of a state of the art facility specifically designed for accelerated endurance testing (AET) of heavy trucks has been completed. The 1 km road features Belgian block, broken concrete, ruts, potholes, sine sweeps, S turns, a turning pad, a curbing event and a frame torsion event. In keeping with modern trends to streamline product development the facility is adjacent to the company's Technical Center and Prototyping facility creating a central, full capability development center. The roughness profiles of the random road surfaces were developed by relative damage calculations using theory of random vibration to establish the proper acceleration factor. A broad range of operating conditions may be simulated by varying speed and event mix. An absolute correlation of the track to other test facilities and field conditions in the USA, Mexico and Canada has been made using a vehicle equipped with 18 transducers. Over 20,000 km of road data has been included in this effort.