This paper addresses the problem of find modular robot's center of mass displacements when a rolling gait is executed on the outside of a pipe. Parametrization of the gait and a complete forward kinematic model was determined in order to find the center of mass position. The displacements the robot's center of mass during a gait will be used as a energy efficiency metric. A stability issue also will be studied, defining a stability margin for this specific gait. Travel in joint space of the actuators depending of the pipe's radius during the locomotion, will also serve as a metric of energy efficiency and at the same time, a measure of gait smoothness. Considerations for energy efficiency, stability and performance of the gait are presented.