In order to be able to work effectively in certain situations such as cramped site conditions, soft verges, etc. small milling machines need a turnable as well as height adjustable travelling drive unit. This means that a travel unit (wheel or track) connected with a pivoting arm can be moved from an outer to an inner position, to create a so-called zero side of the road milling machine. The new concept utilizes the travel drive as an actuator for the pivoting movement of the drive unit. Due to this no separate actuator is necessary.