as per http://www.dpi.wa.gov.au
Alternative road wheels
Alternative road wheels are permitted under the following conditions :
Rim width must not exceed the maximum rim width specified by the manufacturer by more than 25mm (1") (for passenger vehicles manufactured after 1st January 1973, the manufacturers rim width shall be taken as that specified on the tyre placard).
In any event, rim width shall not exceed 177.8 mm (7") unless specified by the manufacturer as standard equipment for the vehicle in question. "No increase in rim width is permitted for vehicles fitted with original equipment rims in excess of 177.8 mm (7") width."
this means we still can not go wider that what is the original width of the rim eg r32 gtr is 16 x 8 factory we can legally put a 17 x 8 but nothing wider