This paper analyses an impact of asymmetrical tension forces, which are occurring in the conveyor belt, on the contact forces in the guiding idlers. It describes causes of an increased wear-out of the conveyor belts due to an asymmetric tensioning of the trans- port belt. There were investigated five measuring points loaded with a symmetrical and asymmetrical tensioning of a specimen section of the pipe conveyor transport belt, using the Friedman test for the factor of asymmetry. The tension force determines also changes of the contact force layouts in the individually investigated idler rolls. A newly developed method was applied in order to identify states of the particular experimental phases for the process of the transport belt tensioning and relaxation. This method is based on differences of the contact force time behaviours. It is possible to present a hypothesis, taking into consideration the obtained results that a side slipping of the run- ning conveyor belt is caused by the tension force asymmetry also on the real operational conditions.