The most fundamental function of an automobile brake system is assuring stable braking effectiveness under various conditions. In a previous paper (2004-01-2765), the author et al. confirmed that the friction behavior of a disc brake during running-in depends on both friction materials and discs’ friction-surface textures. Various friction pairs were tested combining discs finished with roller-burnishing and grinding and five friction materials including NAO and low-steel. Some NAO material exhibited large effects on the difference in friction behaviors between discs’ surface textures. A disc finished with roller-burnishing needed a longer running-in period than that with grinding. In another paper (2011-01-2382), further experiment was conducted by combining eight surface textures (finished under four turning conditions with and without additional roller-burnishing), two NAO materials (with different degrees of aggressiveness), and two rotational directions (LH and RH for a vehicle). Notable phenomena were observed such that coefficients of friction had a peak at the initial stage of testing and there’s difference in those at the final stage between surface textures. These behaviors were reasoned with the contribution of aggressiveness and adhesiveness to friction by comparing coefficients of friction and discs’ surface texture and wear. Friction behaviors at the early stage of use have become more significant since running-in period has been extended due to the application of large discs for better braking performance and the increase of hybrid and electric vehicles equipped with regenerative braking. In this study, therefore, simplified linear (2D) and areal (3D) roughness models with various surface textures were introduced and their behaviors of wear and roughness were numerically simulated. The change of discs’ surface textures along with increasing wear depended on their initial textures. These models and simulation confirmed the effects of surface textures on friction during running-in, which were experimentally observed in the previous studies.