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The main function of any traction device or an off-road vehicle is to produce the largest traction force possible by shearing the soil. For example, the lugs on agricultural tires are used to increase the soil thrust. However, the soil resistance to the shear depends upon the geometry of the shearing surface. Therefore, the position of he lug on the wheel surface, along with the lug shape, affects the traction produced by the lug. Figure 1 illustrates the dimensions defining the lug position on the wheel surface. Definitions of each term in this figure are shown in the Agricultural Engineering (ASAE) Yearbook 1976 The lug space, angle, end-of-lug clearance and splitting of the lug are important variables which define the lug position and affect the soil thrust. Commercial agricultural tires are available in many tread patterns, including different distributions of lugs on the outer surfaces. Comparisons between several lug distributions have been undertaken by several researchers (Vasey and Naylor 1968-Reed and Shields 1950), but relatively few studies have been carried out on the effect of these parameters on the wheel traction characteristics. The information required for the tire designer is the optimal lug position to obtain a desired increase in the traction force, depending on the soil conditions and wheel loading. Several investigations have been carried out on the effect of the shape and dimension of a track on traction (Taylorand Burt 197V Ikeda and Persson 1968). Chang and Cooper (1968) indicated that lugged rubber tires are still in need of more development and there should be a better understanding of the interaction between the legs and the soils.
effect of lug position on soil thrust for lug models
Ali, Omar S. and Edward McKyes 1978. EFFECT OF LUG POSITION ON SOIL THRUST FOR LUG MODELS. Canadian Agricultural Engineering 20(2):119-126.
119 - 126