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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.

As a response to the continuing demand for lower weight and improved driver comfort, Hendrickson Truck Suspension Systems has designed and developed an innovative front steer axle and air suspension module for a 5.5 tonne (12,000 lbs.) axle rating. A system for a 6.7 tonne (14,600 lbs.) axle rating is under development. The suspension is a steel spring and air spring load-sharing system, offering roll stability and handling better than any on highway mechanical system while giving superior ride characteristics. In addition to the suspension, the module features an efficient fabricated steel steer axle and clamp group. The clamp group provides progressive support to the vertical legs of the axle housing with increasing bolt torque, thus maintaining the structural integrity of the box section axle. The complete system is significantly lighter in weight than competitive spring and forged axle suspensions and is designed for minimal maintenance.