In Victoria (and most states I think) -
measure the distance between the tow ball and the centre of the axle (or centre of axle group if multiple axles). This is the "wheelbase". Multiply the wheelbase by 0.6 and this is the overhang your are allowed to have rear of the centre of the axle. If the load protrudes past the rear of the rear bumper/tail light position more than 1.2m you need to attach a red flag to the protrusion during the day, or a red light (ie additional taillight) at night.
Note there is a difference between rear overhang and rear protrusion.
Rear protrusion is the distance between the rear of the body (or bumper, tail lights) and the rear of the load.
Rear overhang is the distance between the centre of the rear axle (or axle group) and the rear of the body/load. No load or body is allowed to go past this point. Example, some large rigid trucks have a tray built to their maximum overhang limit and therefore can't have any load protruding past the tray at all.
The actual formula for rear overhang is "w/b x 0.6 or 3.7m, whichever is the lesser"
I would post a link to an info sheet on the VicRoads website but it is currently "undergoing maintenance".
Peter H
