Hi andys MQ, all the regs covering vehicles for WA are found in the Road traffic (Vehicle Standards Regulations 2002), this is the 'bible' for anything covering mods, specs etc for all vehicles and this is where the 'defect notices' will generally stem from. You can find an on line copy of it at slp.wa.gov.au (and all legislation in WA including the Road Traffic Code and Act and everything else that covers our lives!
In Part the VSR's (Vehicle Standards Regs) say:
69. Alteration of vehicles
(1) A person must not, without the approval of the Director
General, alter a car or a derivative of a car from —
(a) the manufacturer’s specifications; or
(b) its form when it was first licensed, in regard to any part
of its construction, equipment or fittings that was
effected, manufactured or constructed in accordance
with an ADR by making an alteration referred to in the
Table to this subregulation.
Penalty: 16 PU.
Modified penalty: 2 PU.
Table of alterations requiring approval
1. Fitting an engine of greater displacement volume than an
engine that was available as an option for the vehicle with
the same braking system.
2. Making modifications to braking systems which include the
fitting of smaller diameter brake drums, or narrower brake
drums or brake shoes which reduce the swept area of
braking surface or which reduce the weight of the brake
drum or disc.
Road Traffic (Vehicle Standards) Regulations 2002
Part 8 Miscellaneous
page 52 Version 02-c0-03 As at 30 Jun 2008
Extract from www.slp.wa.gov.au
, see that website for further information
3. Fitting any wheel rim with more than a single weld around
the circumference, or which does not conform to one of the
dimensional standards for wheel rims set down in the Tyre
and Rim Standards Manual issued by the Tyre and Rim
4. Widening the wheel track of front or rear wheels by more
than 25 mm beyond the maximum specified by the vehicle
5. Fitting spacers between wheels and hubs additional to any
provided by the vehicle manufacturer.
6. Fitting wheel nuts which do not engage the thread of the
wheel studs for at least the same length as the nuts provided
by the vehicle manufacturer, or wheel nuts which do not
match with the taper on the wheel.
7. Fitting tyres other than those appropriate to the wheel rim
as specified in the Tyre and Rim Standards Manual issued
by the Tyre and Rim Association.
8. Making modifications to an axle, axles or suspension which
reduces the available suspension travel from static
conditions to full bump position to less than two-thirds of
that provided by the vehicle manufacturer.
9. Making modifications to an axle, axles or suspension such
that any part of the vehicle other than the tyre or rim will
contact a road surface in the case of the deflation of any
10. Welding or heating any axle, stub axle, steering arm or
steering knuckle support.
11. Lengthening or shortening the chassis frame, or the body
structure in the case of a vehicle of mono (chassis-less)
As can be seen items relating to wheels and tyres are found in the Tyre and Rim Standards Manual issued by the Tyre and Rim Association, yours for $54 !!!
Otherwise a call to Transport - Vehicle Examiners at either Welshpool or East Perth may help.
So there you go !