The OpenWHEEL i3R hybrid multi-mode mobile robot is introduced with a focus on its climbing mode. This wheeled robot has an articulated frame with two passive and one actuated joint that allow to climb steps through a nineteen stage sequence maintaining its static stability. This work presents a dimensional analysis of the robot climbing capacity to different design parameters such as track width, wheelbase, wheel radius, leg height, mass and mass repartition. A non symmetrical behavior during climbing is also demonstrated and justified: the front axle axle climbs easily whereas the rear axle refuses to climb. We also try to answer the difficult question of the maximum obstacle height that can be climbed for a given geometry of the robot.