In Fig. 7, the variation of the traction force and mechanical power loss along the tooth surface is shown for the same example cases as in Fig. 6. The subscripts *s* and *r* represent the sliding and the rolling traction force, respectively. The value of *F*_{s} and *F*_{r} is defined by integrating the sliding shear stress *τ*_{s} and the rolling shear stress *τ*_{r} in the whole computational domain. As shown in Figs. 7(a), 7(c), and 7(e), the distribution of sliding traction force acts like a sine function. Meanwhile, the rolling traction force is almost negligible compared to the sliding traction force. However, rolling power loss PL_{r} generated by the rolling traction force constitutes an important portion of the total meshing power loss PL_{m}, especially around the meshing position *P* where the pitch point is located at the middle of contact line *KK'*. For the current three helical gear pairs, neglecting the rolling power loss will result in the maximum 10.2%, 28.6%, and 43.6% underestimation of PL_{m} for the tr = 0.5, tr = 1.0, and tr = 1.5, respectively. It is also observed from Fig. 7 that the influence of thermal effect on the traction force and mechanical power loss is significant. Meanwhile, the thermal effect results in the maximum 47.5%, 28.5%, and 17.8% of mechanical power loss error for tr = 0.5, tr = 1.0, and tr = 1.5, respectively.