QLD - 245/30R20 93W Legal?

[nmcswan]

Hi,
Ive got new mags on my car.
They are 20inch and have 245/30r20 93w tyres on them.

Ive searched all over this forum and google and i just dont really understand what is legal and whats not as everyone seems to have their own opinion.

QLD LAWS ARE AS SUCH:
TMR QLD - Modifications

-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.

-The maximum tyre width for a car or car derivative must
not be more than 1.3 times the vehicle manufacturer’s
widest optional tyre.

My tyre placard off the door:
http://i19.photobucket.com/albums/b1...3-12170856.jpg

To my understanding it says i can go as big of a rim as i want as long as the tyre diameter doesnt exceed +15mm or -26mm.
The wheels still sit at the exact same height etc. I can put one of my 15 inch stockies back as a spare and it fits fine.
so does that mean my tyre diameter has not changed at all? or am i confusing myself?

Any help would be great!

ps,
If anyone saves that photo of the tyre placard its off a 2004 VY s2 Executive.

[rambunctious]

Provided you have measured them both, old and new tyres, and not just gone on the fact they look the same then you should be ok on the info you have put up, but I would be measureing the circumference as well because if there is a difference then your speedo will be incorrect.

I would also be carrying the info in the glove box just in case you get an Officer of the Law or Transport Inspector who does not know how to use a calculator or a measureing device.

Come back if you are not sure how to measure them correctly.

[nmcswan]

I asked the Tyre dealer about getting a spare 20 inch and he told me no need as the stock will fit.
I still checked myself just keeping it up against it. I will measure both when I get home.
Is measuring the Tyre circumference the same as any normal circle?
c=2 x 3.14 x Radius?
measuring from the center of the wheel to the outer edge of the Tyre?

[rambunctious]

Yea the stock will bolt on but if it is not the same diameter/circumference then you should really not drive the car too far.

Best way to measure the diameter is place the wheel against the wall standing upright then use a square or spirit level out from the wall across the top of the tyre to measure the distance to the floor the same way you would measure your own height.

For circumference your way will work ? but I find it easier to put a mark on the flat of the tread then measure around the tyre and back to the mark ie the distance the tyre will travel in a complete revolution. If you measure both tyres this way you will be able to work out the difference as a % and in turn work out how much your speedo is out.

The reason I put the question mark in there was because I thought it was 3.28 not 3.14 but it was a long time ago that I left school.LOL