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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Agricultural Engineering

First Advisor

Ralph Alcock


A new approach to the traction prediction equation is described. The suggested equation makes use of soil deformation modulus and physical properties of agricultural tires. Equations for calculating contact patch length and area are also introduced. The novel features include non-linear shear stress distribution and change in the value of soil deformation modulus (K) with the normal stress. A new model, which suggests a relationship between the contact patch area and the soil deformation modulus, is also introduced. The prediction equation was compared with the widely used Wismer and Luth equation and the measured data obtained by Wittig. The proposed approach results in an improvement over predictions obtained by Wismer and Luth equation for net traction. It also involves minimal testing. A newly developed technique of measuring the in-situ K values is proposed. The new technique would give more meaningful K values by taking surface effects and conditions into consideration.

Library of Congress Subject Headings

Tractors -- Tires -- Traction
Shear strength of soils -- Testing




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