There have been many researches about the various utilities of mobile robots and the driving mechanism for off-road mobility. It is necessary for the robot vehicles to play the key roles of search and rescue operations in dangerous areas and unknown terrains, instead of humans. It is a prior issue to develop a driving mechanism that can overcome off-road obstacles to achieve such objectives, such as stairs. Therefore, we proposed a new type of driving mechanism that has a variable geometry single-track. This mechanism has a symmetric configuration so that the robot advances in dual directions and prepares against overturn. By using transformation, it can reduce the maximum energy consumption in steering and rotating and also maximise the ability to overcome stairs.