The performance of magnetorheological (MR) brakes depends on the rheological and tribological properties of MR fluid. An additive-free MR fluid does not offer better braking performance, which limits the commercial application of MR brake. In view of these issues, MR fluids were prepared in this present work employing graphite flakes as an additive. The required rheological properties of these MR fluids were measured on the magneto rheometer, and their braking performances were measured as per braking standard IS13453 using a fabricated MR disk brake on a 2/3-wheeler brake inertia dynamometer. Due to the interaction of MR fluid with the rotor and housing surface, the MR gap (i.e., another performance parameter) varies. Therefore, the effect of the interaction of prepared MR fluids on the rotor surface properties of the MR disk brake was also investigated. The constituents of MR fluids generate roughness on the rotor and housing surface. As a result, a mathematical model for surface roughness was presented and verified with experimental results. Based on the study, it is found that 0.5% (w/w) of graphite flake is better than additive-free MR fluid.