RIM SIZE CHANGE FOR QLD

[Gene FJ20DET]

Rim Size
The rim diameter may be varied from the standard size
but the overall diameter of the tyre must not vary by more
than +15 mm or -26 mm.
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 increase of 26 mm larger than standard and
50 series tyres are fitted to rims with a diameter 50 mm
larger than standard.

General Conditions for Alternative Rims and Tyres
The rims and tyres must not protrude beyond the bodywork
of the vehicle, including flares, when viewed from above and
when the wheels are facing straight ahead. If the vehicle was
originally constructed with a portion of the wheel protruding,
the wheels must not protrude further than originally constructed.

LOW PROFILE TYRE STANDARD TYRE 16
The tyre to rim fitting and the tyre to rim combination must
be in accordance with the Tyre and Rim Standards Manual
published by the Tyre and Rim Association of Australia.
Reputable tyre retailers should have this information
and be able to advise on the correct combinations.
All rims fitted to an axle must be of the same diameter, width
and offset. They must not have a circumferential weld other
than that which attaches the outer rim to the centre.
All rims must have stud hole pitch circle diameters appropriate
to the hub. Wheel nut tapers must be appropriate to the wheel
and must engage the thread of the wheel studs for at least the
same length as the nuts provided by the vehicle manufacturer.
Slotted and elongated stud holes are not permitted.
The fitting of spacers between wheels and hubs, additional to
those provided by the vehicle manufacturer, is not permitted.
The tyre and rim must not foul wheel arches or suspension
components under any conditions. Steering limit stops should
not be adjusted to reduce the turning circle in order to allow
the fitting of the tyres and rims.
The tyres must have a tread depth of at least 1.5 mm on every
part of the tyre that touches the road and not have any
apparent defect that is likely to make the vehicle to which
they are fitted unsafe. It is not permitted to fit tyres that have
been treated by recutting or regrooving unless the tyre has
been marked by the original manufacturer as suitable for
recutting or regrooving.

Tyres
The maximum tyre width must not be more than 1.3 times wider than the vehicle manufacturers widest optional tyre.
However, in the case of off-road passenger vehicles fitted with front and rear
beam axles, the maximum tyre width must not be more than
1.5 times larger than the manufacturers widest optional tyre.
The nominal width of the narrowest tyre fitted to a vehicle must
not be less than 70 percent of the nominal width of the largest
tyre fitted and never less than the vehicle manufacturers
narrowest optional tyre as indicated on the manufacturers
tyre placard.

17 Speed and Load Ratings
The speed rating of all tyres must be:
(a) a speed of at least:
(i) for an off-road passenger vehicle - 140km/h; or
(ii) for another car (sedan, station wagon etc.) up to 9 adult
seating positions or a car derivative - 180km/h; or
(iii) for another motor vehicle - 120km/h; or
(b) the vehicles top speed, if lower.
Load ratings of tyres must be at least equal to those specified
by the manufacturer on the tyre placard fitted to vehicles made
after 1972. For other vehicles, the load rating of a tyre must
be capable of carrying the part of the vehicle’s gross mass
carried by the tyre.

Tyre Construction
Tyre thread compounds, patterns, ply ratings and performance
characteristics vary. Tyre construction (e.g. radial) and size must
be the same on the same axle. Although it is recommended
that the tyres are identical (i.e. same brand and tread pattern),
this is not mandatory.

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 wheel track must not be reduced to less than the standard
track specified by the vehicle manufacturer for the particular
model of vehicle.
The track of a car or car derivative may be increased by up to
26 mm beyond the maximum specified by the vehicle
manufacturer for the particular model of vehicle. Off-road
passenger vehicles fitted with front and rear beam axles,
may have an increase in track up to 50 mm beyond the
maximum specified by the vehicle manufacturer for the
particular model of vehicle.
Wheel Marking
Vehicles built on or after 1 July 1985 must be fitted with
original wheels or replacement wheels which are indelibly
marked in accordance with approved standards.

These include:
Standards Australia;
Wheel Industries Association (Australia);
Technischer Uberwachungen Verein; and
Japanese Industrial Standards.
Markings must include diameter, width, offset and the
manufacturers trade mark or logo and be located so that
they are readily visible when the wheel is correctly installed
on the vehicle.

Composite Wheels
The use of composite wheels (two or three-piece) is
permitted. They must be manufactured and marked in
accordance with the standards described above if fitted
to vehicles manufactured after 1 July 1985.



So a run down of that is as follows

Diameter = Tyre + Rim diameter must not be greater than 15mm or less than 26mm eg you must match the oe diameter with lower profile rubber.

Width = max of 1.3x the OE tyre width size (example 225 tire = max 292.5) also front and back tyre width difference is 70% so the front can't be less than 70% of the back. eg NO FRONT RUNNERS!

Handy link too http://www.transport.qld.gov.au/qt/driver.nsf/files/images/$file/Vehicle-Modifications.pdf
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[TGemi1]

so can we run 16's with 35series? or 15's with 50series
too dumb 2 work out

chris...

[Gene FJ20DET]

u can run 30" aslong as the rolling diameter is the same
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[Gene FJ20DET]

15" - 50 series
16" - 45 series
17" - 40 series
18" - 35 series

at a guesstamate
theres a tiresize calculator in the r&d somewhere
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[Loz]

http://www.miata.net/garage/tirecalc.html

a gemini with 205/40 R17 will be something like 5.6% faster.

Who can say exaclty what size geminis originally had. Everyone seems to think different things.

[Adam]

Er... it is written on the tyre placard.

[TXcoupe]

there original tyre size was a 155/80/13 or a 165/75/13 these are gathered from the codes on the placard in the glovebox.

[Loz]

cheers.

I didnt know what the numbers were saying as there wasnt a specific tyre size written on there.

[Poida]

The tyre and rim sizes are also listed in the owners handbook.

I have posted a fairly extensive document relating to standard wheels and tyres at this location.
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I try to tackle one day at a time, but often several days attack me at once.



(The views I present are my own and NOT necessarily of the administrators or other members of this site.)