THE MOTOR-TRUCK TIRE IN ITS RELATIONS TO THE VEHICLE AND TO THE ROAD1

In motor-truck impact-reactions, the unsprung component is generally the major quantity and the force depends on four principal variables: tire equipment, load, speed and road roughness. The tire equipment that utilizes the greater time of duration for the reaction will cause the lower impact-forces. Increases in load, speed and road roughness increase the impact-reaction. Poor tire-equipment on rough roads may cause forces of 35 tons to be borne by both the truck and the road. Pneumatic tires rarely allow reactions greater than twice the static wheel-load. The impact reactions of a six-wheel truck approximate one-half those of an otherwise equivalent four-wheel truck having the same pay-load. Fifty per cent loss in the overall height of the tire multiplies the impact reaction by 2.5. Rolling resistance varies with the speed, the tire equipment and the road surface, and may reach a value of one-sixteenth the wheel-load. Gasoline consumption at 10 m.p.h. on solid tires equals that at 25 m.p.h. on pneumatic tires. Data concerning forward and sidewise skidding are given for wide ranges of conditions.