The main goal of this paper is to establish an interference tolerance for determining optimal amount of clearance in a shaft-bearing system supported by ball bearings. A 2-D frictional contact model is employed for the FE analysis on the plastic deformation between shaft and inner raceway. Several examples are simulated for different material properties of shafts. Solid shaft are selected to investigate how the selection of geometrical shapes influences on radial load in quantitative manner. Main efforts are focused on the deformation applied in the radial direction as selection of suitable bearing. The proposed design parameters obtained by numerical simulations can help predicting a rate of bearing life reduction as functions of shaft diameter ratio. The results of analysis in this paper also could be used to predict the optimal clearance in the radial direction in order to design a shaft-bearing system for higher accuracy and longer longevity of bearings.