because a wheel rim meets a DOT or mining standard, it does not mean that a truck fitted with those wheels is therfore roadworthy or "legal". If you fit wheels that have a rolling diameter greater than 15 mm above what is stated on your tyre placard, not only could your truck be put off the road until it was put right but you could be found liable in an accident. There are other factors here that also need to be complied with such as speedometer accuracy but regarding the fitting of larger single rear wheels, you will find most state legislation in Australia looks like South Australia's current legislation quoted below:
(5) Despite the requirements of any other regulation or rule under the Act, a motor vehicle that is required to comply with ADR 24 or the tyre and rim selection requirements of ADR 42 may be—
(a) equipped with tyres other than those listed on the tyre placard fitted to the vehicle, provided that—
(i) the load of a tyre fitted is not less than the lowest load listed on the tyre placard; and
(ii) the overall diameter of a wheel and tyre fitted is not more than 15 millimetres greater than that advised in the Tyre and Rim Standards Manual (issued by the Tyre and Rim Association of Australia) for the largest tyre size listed on the placard and not more than 15 millimetres less than that advised in the Manual for the smallest tyre size listed on the placard; or
(b) equipped with wheels wider than those listed on the tyre placard; or
(c) equipped with wheels with a rim diameter other than a rim diameter (if any) listed on the tyre placard.
So there is a lot more to doing a SWC conversion properly and legally than fitting an "approved' rim or sufficiently load rated tyre. I would also add that most mines I have dealt with are very reluctant to fit any aftermarket components onto a Canter or Isuzu truck that does not meet ADR compliance ......even if the vehicle is unregistered and running around a closed site.......In our days of OH&S litigation the mines are usually too worried that they may be somehow making a vehicle (seen by them as a workplace) unsafe.