This paper describes a novel solution to a mobile climbing robot on magnetic wheels, designed for inspecting the interior surfaces in gas tanks made out of thin metal sheets. These surfaces were inaccessible by previous climbing robots due to the following restrictions: 1. Ridges, where the magnetic force decreases to almost zero 2. Angular transitions between the surfaces (135°) 3. Thin metal sheets that cannot provide high magnetic forces The main optimization criterion for this robot was to design it as light as possible, as the surface was also considered to be very fragile. As the here described type of application is very special and was not examined much in previous publications, this work also stresses on the early analysis phase. This phase mainly consists of tests to optimize magnetic wheels for thin surfaces and mechanical calculations for robots on magnetic wheels. The chosen concept is described in detail, explaining how the robot moves around and passes the obstacles. The analysis of the most critical cases is presented, as well as some details about magnetic wheels and actuators.