TRACTOR TIRE ASPECT RATIO EFFECTS TRACTOR TIRE ASPECT RATIO EFFECTS ON SOIL STRESSES AND RUT DEPTHSON SOIL STRESSES AND RUT DEPTHS

Abstract

A 580/70R38 tractor drive tire with an aspect ratio of 0.756 and a 650/75R32 tire with an aspect ratio of0.804 were operated at two dynamic loads and two inflation pressures on a sandy loam and a clay loam with loose soilabove a hardpan. Soil stresses were determined just above the hardpan beneath the centerlines and edges of the tires. Rutdepths were measured at the centerline and edge of each tire track. The octahedral shear stress and rut depth were notsignificantly different for the tires. The peak octahedral normal stress was not significantly different for the two tires whenthe dynamic load was 17.2 kN, but was significantly greater for the 650/75R32 tire when the dynamic load was 30.9 kN.Soil stresses and rut depths increased with increasing dynamic load at constant inflation pressure, and with increasinginflation pressure at constant dynamic load. Net traction and tractive efficiency decreased with increasing inflationpressure at constant dynamic load. At constant inflation pressure, tractive efficiency increased with increasing dynamicload. In comparisons of the centerline and edge locations, soil stresses were significantly less beneath the edges than thecenterlines of the tires. Ratios of the mean stress beneath the centerline to the mean beneath the edge for fourcombinations of dynamic load and inflation pressure ranged from 2.18 to 3.77 for the peak octahedral normal stress and1.76 to 3.18 for the corresponding octahedral shear stress. Ratios of the rut depth at the centerline to the edge rangedfrom 1.04 to 1.49. In summary, for these two tires with their slightly different aspect ratios, no fundamental differenceswere found that would clearly indicate that one tire was better than the other.