For a motor vehicle and trailer combination that has a GCM of less than 4.5 tonnes, the posted speed limits apply, however, in Western Australia, maximum 100km/h speed limit applies when towing.
When the motor vehicle and trailer combination (GCM) exceeds 4.5 tonnes, vehicle users should consult with the appropriate State or Territory transport authority regarding speed limits. A safe speed, satisfactory stopping distance and any other requirement imposed by the manufacturer of the towing vehicle also apply.
For certain road conditions (e.g. sharp bends, steep descent, winding roads), special speed limit signs may be posted for trucks, road trains and buses. You must not drive at a speed greater than the speed shown on the sign.
If the posted speed-limit is over 100km/h and the RV or vehicle and trailer have a GCM over 5 tonnes, or any other vehicle with a GVM over 12 tonnes, the speed-limit applying to the driver for the length of road is 100km/h (Australian Road Rules – February 2009 version).