The helical gear pairs are widely used in different mechanical constructs. The main advantage is the good efficiency and the low noise during the connection.We have worked out a computer software with which the designing process of the helical gears could be eased. Based on the calculated gear parameters the CAD models of the elements could be prepared. Knowing of the geometries the assembly could be created based on the fixed freedom degrees and the elementary centre distance. We have designed five types of gear pairs. The differences are only the different tooth traces. All of other parameters have not been modified. We have done TCA which is meant we have analyzed the effect of the modified parameter for the normal stress, normal deformation and the normal elastic strain on the contact zone. Based on the results we have prepared diagrams for the analysis of the correlations between the changing parameters.