In general, slipping and sinking on the rough terrain is lead to poor condition for planetary explorations robot, which is equipped with a cylindrical typed wheel. Meanwhile, in a robot, which is equipped with inching worm locomotion, slipping and sinking lead to increase a traveling performance because the more sinking and slipping of the robot is, the larger the bearing force in the back of a wheel increases. Moreover, in the inching locomotion, the wheel travels during sharing soil beneath the wheel and pushing soil in backward. However, this model was not investigated before. This paper investigates the relationship between the bearing force in the back of the wheel and sinkage. For analysis, firstly, this paper performs theoretical consideration and numerical simulation of a bearing force using bulldozing resistance model. Secondly, this paper performs wheel bulldozing experiment. In order to investigate the difference of bearing force when the wheel size is changed, this paper sets three wheel size. From the simulation and experimental results, the Hegedus's model corresponds with the experimental results in each wheel size. Additionally, the bearing force was observed to increase when the sinkage was increased. Thus, the ability of the inching locomotion using deep sinkage is high.