This paper considers the mechanical interaction due to surface roughness and examines the surface theories using the classical definition of coefficient of friction: the tangential-to-normal load ratio. The aforementioned postulation for maximum static friction is used to experimentally evaluate the contact models. For this purpose a pin-on-disk test apparatus is employed with the capability of measuring tangential and normal forces for a frictional contact. The tests involve pairs of disk and specimen, i.e. Steel-on-Steel and Aluminum-on-Aluminum contacts. In each case profilometer measurements are performed on the disk and the Greenwood and Williamson parameters are determined. Using the parameters the theoretical estimates of normal and tangential loads are obtained. The theoretical values of tangential-to-normal contact force ratios are compared with those obtained from measurements for various applied normal loads. The tests utilizing a pin-on-disk apparatus showed that reasonable agreements between experimentally obtained load ratios and those predicted using the theoretical elastic and elastic-plastic contact. The agreement was found to be most favorable in the case of elastic-plastic model.