Agricultural tractors have been developed over the years to carry out almost every operation on the farm. However, they are not ideally suited to all these tasks and it may be more economical, in certain situations, to use more specialised vehicles. In the extreme, one could perhaps imagine four different types of agricultural vehicles, for heavy draught work, transport, low ground pressure applications and materials handling. Computer models are being developed to evaluate the potential economic benefits which might be achieved by the introduction of such specialised vehicles on particular farms. Models already exist for predicting tractive performance and average speed over different types of terrain. Further models are needed for manoeuvrability and some other aspects of performance.