The elements creating friction pairs are described to be very difficult in terms of determining all optimal parameters in an unambiguous manner. The nowadays research on stability of friction pairs is focused on the surface and the top layer of surface. The main goal is find new design solutions and materials, achieving a lot of kilometers to main repair in combustion engines. The biggest structural difficulties are noticeable in friction pairs where can be observed sliding and returning motion, what is connected with sealing function. A typical example of such pair is piston ring – cylinder. Engineers work on defining an additional factor that would be able to gain the reduction of tangential force by reducing the friction coefficient in elements of friction pair. Molecular structure and nature of the bonds between the molecules presented in the material, result that the free surface energy may be such a factor, because determines the tribological properties of the material, what is reflected in the stability of the units. The work carries out of an analysis after research on the goniometer in the presence of water and diododomethane that allowed to measure wetting drops on the surface, thanks to which can be calculated surface energy. Within this work will be performed study of the energy state of the surface of piston rings with a coating including a diamond powder. After analysis on the basis of the collected measurements will be developed conclusion regarding the potential relationship between the free surface energy and wearing of the material.