That rule went out about 15 years ago.....The old rule used to be 2" bigger than the biggest factory option available........So considering a VK did come with a 16" rim, you are in correct in your statement to begin with...16" Brockadore wheels were classed as a factory option. And even the 15" wheel fitted to the VB still meant a 17" wheel was still legal to fit way back then
all that is a crock...
the rule in Victoria was ALWAYS only +1 .. based on the MANUFACTURERS spec. NO VK Commodore ANY MODEL came with a
standard 16" wheel!
period!
(beware that Vic police know this as I have been always been informed now and then by my next door and cousin who are Vicpol members (one at the Moorabbin traffic management unit).... despite what car clubs and social media say) HDT took advantage to go 16s ....but they does not allow you to go 16 +1!
HDT Commodore 16" wheels are NOT a factory option, never were, never will be, they were always a HDT option. The 16 inchers were supplied to GMH by HDT and if requested by the buyer fitted then .
so as I have previously stated, 17 inch (or larger wheels ) on any Commodore are unroadworthy in Vic .. and if my neighbour or cousin spot you with them and they are having a bad day.. they say so will you ! There is a but though....
If you have an engineers report for larger wheels. keep it in the car!