Abstract: Previous study on the disc brake comfort was only about brake shell protuberant limiting the place of the platen protuberant, but their collision was not studied. This paper presented the study on the comfort during braking, analyzed the main factors affecting the comfort, pointed out that the collision is the radical reason causing discomfort. It's the collision that makes sharp increment of the relative increase rate of brake moment and the brake discomfort. Reducing the circumferential gap between the platen protuberant and the brake shell protuberant can reduce braking impulse and improve the comfort effectively.