79 Analysis of force efects measured in the tractor three-point linkage J. Čupera, F. Bauer, L. Severa, M. Tatíček Faculty of Agronomy, Mendel University in Brno, Brno, Czech Republic Abstract Čupera J., Bauer F., Severa L., Tatíček M., 2011. Analysis of force efects measured in the tractor three-point linkage. Res. Agr. Eng., 57: 79–87. Te work is focused on description of tractor individual axels and wheels loading during ploughing. A combination of tractor inclination with force and momentum efects need not always result in marked diferences in the load of driving wheels. Tis paper documents the relationship existing between forces working in the upper drawbar F h of the three- point linkage and the momentum M Tx . It was also demonstrated that with the increasing value of M Tx the diference between loads of both rear wheels reduces. Te described algorithm enables to evaluate output parameters of ploughing aggregates for diferent variants of forces changing in the tractor three-point linkage due to various ways of suspension and adjustment of individual plough types. When using data recorded in the course of ploughing operations it is possible to demonstrate the efect of plough adjustment/attachment on the efciency of the whole ploughing aggregate. Keywords: three-point linkage; wheel load; load cell Supported by the Ministry of Education, Youth and Sports of the Czech Republic, Project No. MSM 6215648905 and Internal Grant Agency TP1/2011. Te development of tractors and tools directed to system with either attached or trailed machines resulted in certain discrepancies between the man- ner of operation of tractors and the methods of measuring their tractive properties. Attached and/ or trailed sets of machines are characterised by the fact that the tools are connected with the tractor by means of a three-point linkage so that their result- ing force efect on tractor is usually markedly dif- ferent from efects of simple tractive forces, which typically exist in each tractive test of tractors. Measurements of forces existing in the three- point linkage of a tractor and the projection of measured force efects into its centre of gravity were described by Bauer et al. (1989). Results of the frst experiment with the determination of efects of the ploughing operation on soil compaction were pre- sented in a paper published by Mišun and Bauer (1992). Problems associated with force efects of ploughs on tractors ploughs kinematics were stud- ied by many authors (Kazzaz, Grečenko 1968; Upadhyaya, Kemble 1985; Sloboda et al. 1997; Mouazen et al. 2009). Also other factors afect- ing drawbar characteristics such as tire infation and others were deeply studied (Novák et al. 2009; Šmerda, Čupera 2010). Te objective of this paper is to describe forces infuencing wheels of a ploughing tractor and to fnd out which of them put a concrete load on driv- ing wheels because the driving wheels are of cru- cial importance for the tractor’s tractive efciency. Concerning tractive efciency, there is a concern to reach the maximum values of this factor but, re- garding efects of an undesirable compaction of soil (and subsoil), the adhesion load of driving wheels is in confict with this requirement above all in case of Res. Agr. Eng. Vol. 57, 2011, No. 3: 79–87