Yes I have seen this "code of practice" but it's not an ADR specification and seems to only apply to "light vehicles" with "with standard axles and suspension" but not sure how this is applied in the various states or in the case of 4WDs or trucks.IcedVolvo, what about the requirement for the singles to be a minimum of the width of the duals combined? (if you're under 4500)
For example it is certainly not applied in heavy trucks where typically a 445/70R22.5 super single replaces a standard dual 275/295 fitting.
I think as long as your rim/tyre load ratings are within spec (and are AS approved for its use) you are probably OK.
The other poster is correct: Australia is a mess with all its various state rules/regulations/codes of practice and overlapping federal ADRs etc. We really should just have one set of rules! At the moment the easiest place to get registered is QLD. But once registered it is impossible to move states. For example my truck is registered in QLD but if I wanted to move it to NSW I have to get new NSW engineering certificates for every single modification to the truck; the local engineer simply told me to forget it as he would require mechanical drawings/specifications for EVERY single structural component not fitted on the vehicle as supplied by ISUZU. The cost to get new NSW approved engineering plates could exceed $30,000 so in Queensland it stays!
The ideal situation is to get Federal registration which means you only have to obey the ADRs and any qualified engineer can sign off. I almost got it as I live right on the border and the truck is registered in the company name and crosses the border several times a day. But fell over at the last hurdle as some bureaucrat in Canberra insisted that the rules require that the truck's PURPOSE must be to "move freight or passengers between states" whereas I was only "conducting business between states". In the end the easier option was to down rate to 4500kg in QLD: no inspections and far less dramas with police/RTA etc.
As WhatcharterBoat is saying: its better to have all the boxes ticked it's just knowing which box to tick in which state that's the problem!!!