wheel width laws

[Gts-t]

On a car in queensland that comes standard with the same width wheels front and rear, for example my HCR32, is it roadworthy when upgrading wheels to have different widths front to rear.

ie. 18x7.5 F

18x8.5 R

instead of standard

16x6.5 F+R

i know that the tyres must be the same side to side. .just concerned with

1. how many inches wider than standard i can go and be roarworthy

2. if i can run wider on the rear than the front and stay roadworth

surely there are heaps of people here running non stanard rims that can shed some light. are r33's same width front and rear? what about r34's

thanks!

[WiZardOz]

Extract from Qld Transport Vehicle Modification Guide

Full version of the guide can be dowloaded here

http://www.transport.qld.gov.au/qt/driver....dex/vehiclemods

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 (50, 60 or 65 series), replacing standard

profile tyres (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.

A diagram of this concept appears below.

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.

[WiZardOz]

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.

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”.

[WiZardOz]

Tyres

The maximum tyre width must not be more than 1.3 times wider

than the vehicle manufacturer’s 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 manufacturer’s 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 manufacturer’s

narrowest optional tyre as indicated on the manufacturer’s

tyre placard.

Hope this helps to educate all

[Gts-t]

thanks gary.. i was looking on the net this morning tryin to find something like that.

by the sounds of all that i can run different widths front to rear.. but same widths per axle. i shoud be legal upgrading from

16x6.5 205 F+R

to

18x7.5 215/40/18

18x8.5 225/40/18

anyones experinces would help.

[chaos]

you can actually got quite larger than that

[callmaster]

from an insurance company point of view.. make sure u check with them as to what they accept or not... most have their own guidelines, so regardless of whether it is legal from qld transport, ur ins company wont pay out if something happens...

[slip]

1.3 times widest OPTIONAL tyre. Some research could get you some more width to play with.

Chaos said you can got quite larger than that..... He means to say you can go quite a bit wider than that, wether it is legal or not is another story.

[chaos]

yeh thats what i meant

[51jay]

225 is a bit undersized for an 8.5ins rim the optimal size on that rim would be 245 I would have 225 front and 245 rear or maybe 255 rear

[Oz]

as a rule though 2 you are (this is mind you a little old so don't know if it has been changed ) only able to change the rim size 2 inches larger than the biggest factory fitted wheel so 16" --> 18" is ok