There is regular debate as to whether extended mirrors are required when towing. The field of vision required by a vehicle’s external mirrors is set out in the Australian Design Rule 14/02 – Rear Vision Mirrors.
The field of vision must be such that the driver can see at least a 4 m wide flat, horizontal portion of the road which is bounded by a plane parallel to the median longitudinal vertical plane passing through the outermost point of the vehicle on the passenger’s side and which extends from 20 m behind the driver’s ocular points to the horizon (see Figure 5). In addition, the road must be visible to the driver over a width of 1 m, which is bounded by a plane parallel to the median longitudinal vertical plane and passing through the outermost point of the vehicle starting from a point 4 m behind the vertical plane passing through the driver’s ocular points.— Australian Design Rule 14/02 - Rear Vision Mirrors
Simply, you are required to see along the full length of your caravan or camper trailer at its widest point and a further 20m behind this. To further simplify this, your mirrors should be wider than what you are towing.
Your mirrors should be wider than what you are towing
The above diagram shows the difference between using towing mirrors and standard mirrors. Without the towing mirrors there is a large blind area.
With most caravans, it is likely that you will require towing mirrors. You can either purchase extendable mirrors to replace your vehicles existing mirrors or towing mirrors that will attach to your existing mirrors.
Remember to only have your mirrors extended when towing. There are ‘over-dimensional’ laws which are taken from Australian Design Rules that state nothing is permitted to protrude more than 150mm from the side of a vehicle. When towing, the widest part of the caravan or camper trailer is deemed to be the side of the vehicle. Therefore, when your caravan or camper trailer is detached, you must fold in or remove your towing mirrors to avoid hefty fines.