1. Theory of Land Locomotion;Bekker,1962
2. Power requirements of rotary tiller blades in clay and sandy soils;Perdok,1977
3. A dimensional analysis of the performance of pneumatic tyres on soft soils;Freitag;W.E.S. Tech. Report no. 3–688,1965
4. Application of similitude to soil-machine systems;Wismer;J Terramech.,1976
5. St. Christopher Lecture: Agricultural Engineering and Terramechanics;Söhne,1969