Selection of tyre sizes for agricultural vehicles.

Abstract Empirical equations are given from which the tractive performance of tyres in off-road conditions can be predicted. The equations are used to demonstrate the effect of varying tyre diameter and width on a lightly loaded and a heavily loaded axle in different field conditions. The effect of varying tyre flexibility is also demonstrated. The equations are used to derive curves giving the axle load required per unit of available axle power to ensure operation at maximum efficiency in any field condition. The maximum possible tractive efficiency is calculated. The results of validation experiments on the effect of fitting larger tyres and ballasting to the optimum level are given. The relative performance of dual tyres and a single tyre of the same overall dimensions is examined as is the relative performance of a single large type and two smaller tyres used as duals. The loss in performance due to the use of high inflation pressure high load carrying capacity tyres such as earthmover tyres, in place of agricultural tyres is shown.