One of the major challenges of our generation is the sustainable usage of the resources available on planet earth and the reduction of emissions and pollutants. Besides the usage of alternative energy sources, such as photovoltaics, hydro or geothermal energy, the optimization of already proven technologies bears a high potential for improvement, combustion engines for instance, have friction losses of about 30% of the currently provided horsepower output. Due to these circumstances and requirements of legislation and companies, detailed analysis and sophisticated optimization of non-conforming contacts, such as camshafts or gears, are necessary to treat the rising demands. This thesis deals with different surface modification processes, namely shot peening, vibratory finishing and grinding, and their effects on the performance of tribological systems. The employed methodology consists of three major parts. Firstly experiments are carried out using a two-disc test rig, whereby temperature, speed, load and slip are set and temperature, friction force and contact potential are measured. Secondly, the surface microstructure is investigated through a laser confocal microscope, the data is then processed further into an in house developed software for 3D surface evaluation and 3D parameter calculations. Finally numerical simulations are performed, employing a newly developed mixed friction model, which has been created on basis of existing projects, in COMSOL Multiphysics. To generate accurate results, surface data of the surfaces investigated, is imported into the simulation software. Results reveal, that a sophisticated application of shot peening and vibratory finishing (SPVF) yields an outstanding frictional performance in comparison to grinded surfaces. In some cases the COF is reduced by a factor oft two, which is a remarkable result. SPVF surfaces have an extremely smooth plateau structure, which still contains small dimples. Therefore a hydrodynamic pressure build up and a low COF are possible, even at very low speed. No running in is required for these kind of surfaces, as detailed optical analysis of he specimens show. Furthermore, surfaces that have been vibratory finished (VF) only, perform just slightly better than surfaces only grinded. The highest friction is found when applying the shot peening process (SP). Due to the very rough surface the friction is quite high, however running in is still possible, as detailed investigations of surfaces reveal. It is remarkable that the COF is about 10\% lower for surfaces, which have completed the running in process. The comparison of different surface parameters shows, that the statistical value skewness is a strong indicator of the tribological performance of the surfaces, especially low values are favorable. Numerical computations confirm, that it is highly significant to know the COF of asperity contacts, in order to perform accurate numerical simulations for low speed and therefore low film thickness. Contrary, at high speed, asperity contacts are often negligible, fluid friction dominates and the consideration of non-Newtonian fluid behavior is key. The results, which have been obtained by applying a methodology consisting of experiments, optical analysis and numerical simulation, can be utilized for sophisticated optimizations of the surface structure of a wide variety of non-conforming contacts.