The surface texture of a brake disc in some cases affects the braking effectiveness of a vehicle in the early stages of use. Brake discs usually turn in one rotational direction during their finishing process but are turn in two directions on a vehicle. This causes a difference in friction or wear between two wheels. Directional surface textures of brake discs finished by turning or roller burnishing may cause this interaction to become more severe than those finished by grinding. Full-scale tests using actual friction pairs are effective for estimating the total braking performance of a full vehicle or its corners. However, they are exposed to various factors and different brake-disc locations creating different friction and wear histories. The author, therefore, concluded that fundamental experiments using small-scale specimens are necessary to examine the details of the interaction between the disc surface texture, rotational direction, and friction material. In this paper, the author reports the results of the first series of experiments, which consisted of thirty disc surface textures and a friction material under an on-brake-drag condition. Disc surfaces were finished by turning with normal and wiper inserts, roller burnishing, and grinding. Contact-pressure dependency of friction and wear was confirmed in preliminary tests and the pressure, which caused the largest difference among the tests, was selected for the main tests. The findings from the test results on friction, wear, and transfer-layer buildup are presented and the effects of disc surface textures on friction and wear are discussed.
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