This is some of the Qld Transport info on wheels:
Vehicle track
Track is measured at ground level from the centre of the
tyre on one side to the centre of the corresponding tyre
on the opposite side of the vehicle. Front and rear track
differs on many vehicles.

The track of a car or car derivative may be increased
by up to 26mm beyond the maximum specified by
the vehicle manufacturer for the particular model of
vehicle.

Low profile tyres
It is common practice for manufacturers to fit low
profile tyres to high performance motor vehicles as
standard equipment.
Low profile tyres (e.g. 50 series), replacing standard
profile tyres (e.g. 70 series or above), are normally fitted
in combination with rims of larger than standard
diameter to maintain the correct overall diameter of
the wheel.

The rim diameter may be varied from the standard size
but the overall diameter of the tyre must not vary by
more than +15mm or -26mm.
These limits have been set for a number of reasons.
Varying the overall diameter of tyres affects ground
clearance, centre of gravity, brake effectiveness, steering
geometry, performance and speedometer accuracy.
Generally, to meet these limits, 60 series tyres are fitted
to rims with a diameter 26mm larger than standard and
50 series tyres are fitted to rims with a diameter 50mm
larger than standard.