Performance of Soils under Tire Loads. Report 4. Analysis of Tests in Sand from September 1962 through November 1963

Abstract : This report examines the effects of tire deflection, tread, carcass stiffness, construction, speed, and slip on tire performance in a dry sand. Laboratory tests results indicate that for best performance in a dry sand a tire should be highly deflected, smooth, and of diagonal-ply construction. Variations in carcass stiffness have negligible effects on tire performance when comparisons are made at equal loads and deflections. It was concluded that the performance of pneumatic tires in sand is affected by speed; however, the extent of this influence was not wholly determined. Logical, orderly relations are shown between slip and several independent and dependent variables--wheel load, soil strength, pull, and sinkage--both at the towed and the maximum pull points. A direct relation is shown between the pull developed by a full-scale 4x4 vehicle and that developed by a single wheel in multiple passes. Good agreement was attained in this relation for both Yuma (desert) and mortar sand. Significant differences in tire performance registered in Yuma and mortar sands at corresponding levels of soil strength (as measured by cone index) prompted a study of the physical characteristics of the two soils. This study revealed notable differences in the strength characteristics of Yuma and mortar sands that explain a portion of the differences in tire performance in the two sands.