1. Zur Frage des Allradantriebes von Ackerschleppern;Sonnen;Land techn. Forsch.,1962
2. R. Franke. Four-wheel drives. Paper presented at an Open Meeting on 15th Jan. 1963.
3. Traction tests of a tandem-tractor;Richey;Trans ASAE,1959
4. Effects of two-wheel and tandem drives on traction and soil compacting stresses;Reed;Trans ASAE,1959
5. Theory of land locomotion;Bekker,1956