A wide choice of surface roughness parameters is available to characterize components@ such as gears or bearings@ with the goal of predicting the performance of such metal-to-metal contacting parts. Commonly in industry the Roughness Average (Ra) or the Mean Peak-to-Valley Height (Rz (DIN)) is chosen to calculate the Specific Film Thickness Ratio for both superfinished and honed surfaces. However@ these two surface roughness parameters fail to adequately predict the performance properties of surfaces that are superfinished or surfaces that are honed. In this paper@ a superfinished surface is defined as a planarized surface having a ??.25 mm Ra. A honed surface is not considered to be planarized@ even with a finish of ??.25 mm Ra. Thus@ one is falsely led to predict that a planarized surface or a honed surface@ having an equivalent Ra or Rz@ will perform similarly. Experimentally@ an isotropic planarized surface delivers superior performance. The following discussion utilizes another roughness parameter@ 3??0@ to further explain this phenomenon.