Greetings all!

As the title suggests I'm planning to upgrade my wheels from my stockies @ 15 inches to a set of RJR Phantoms that are 18 inches in diameter.... now I'm wondering if such move is illegal here in victoria? I remember reading from vicroads that:

"The overall diameter of any replacement rim and tyre must not be more than 15mm grater than the largest diameter tyre specified by the vehicle manufacturer for that model or vehicle series"

Now I'm a little perplexed whether about the last statement about the vehicle series/model.... I currently have a exec and it comes stock with 15" wheels - would that mean that legally I can only get a 16" wheel? Or are they talking about the entire Magna line? If so then I would be allowed to get 18's as the VRX came with 17's stock.

I'm also wondering whether the 18 inch mags will knock out my speedo to the point where I'll be traveling faster than than shown on the dash? If I'm traveling at a slower speed that whats listed on my speedo I would be happy as I cannot afford to get a speeding fine when I'm back on the roads, but if its going to give me false readings that could give me a speeding fine then I would need to know.

Thanks for you all your help!

Regards,
TheKovac

try out the Miata (http://www.miata.net/garage/tirecalc.html) tyre calculator. Put in the specs for your current tyre and what the tyre on your 18's will be. As long as the diameter difference is less than 15mm between the two, you be good to go. It will also tell you how the change will affect your speedo.

Largest size is a VRX 17" so cant be more then 15mm bigger in overall rolling diameter.

;1195823']Largest size is a VRX 17" so cant be more then 15mm bigger in overall rolling diameter.

Well my car is an exec model (as you know) so can I still legally get 18's then ? Is that statement about the model or the highest rim size for any car within that model?

It's talking about tyre diamter nothing to do with rim size

Well, says vehicle series, yours being a TJ Would be the 17" VRX rim, so 18/19's would be fine (JUST) 20"s would be more then 15mm rolling diameter

tyres and rims are 2 different things

for instance if they made a 25profile tyre for a 20" rim there really isnt any reason you couldnt put a 20" on your car except that you might hit interference issues

I believe the law states that (somebody correct me on this) that you can only increase the size of the rim by 2inchs greater than your current (or the size as so stated on your wheel plate) so eg. 15-17, 16-18, 17-19 etc. etc. etc. though this is not often checked or scrutinized, if your being checked for that, odds are cops going the tonk on you, and pulled you up for something else first.

Just like other mods that fall in that oh so large grey area, dont draw bad attention to yourself and you normally wont have to worry too much though.

I believe the law states that (somebody correct me on this) that you can only increase the size of the rim by 2inchs greater than your current (or the size as so stated on your wheel plate) so eg. 15-17, 16-18, 17-19 etc. etc. etc. though this is not often checked or scrutinized, if your being checked for that, odds are cops going the tonk on you, and pulled you up for something else first.

Just like other mods that fall in that oh so large grey area, dont draw bad attention to yourself and you normally wont have to worry too much though.

The 2in increase rule has not been used for a long time.

http://www.drive.com.au/Editorial/ArticleDetail.aspx?ArticleID=52051&IsPgd=0

In Victoria the maximum width of any replacement rim can’t be more than 25mm, or one inch greater than the widest wheel specified by the manufacturer for that vehicle or model.

The overall diameter of the rim can’t be more than 15mm more than manufacturer specifications, while the rim and tyre are also not allowed to foul the bodywork or suspension.

http://www.vicroads.vic.gov.au/NR/rd...340/0/VSI8.pdf

Just put 18 inch on my rada...Dropped the series,or height of actual rubber from 60 to 40,so I added 50 mm to the height of the rim but took 40mm out of the height of the tyre,so in rough terms I am 10 mm higher than started,looks a heap better as well but would safely fit into your guidelines...Just do it..but put 35,or 40 series tyres on

Just put 18 inch on my rada...Dropped the series,or height of actual rubber from 60 to 40,so I added 50 mm to the height of the rim but took 40mm out of the height of the tyre,so in rough terms I am 10 mm higher than started,looks a heap better as well but would safely fit into your guidelines...Just do it..but put 35,or 40 series tyres on


mate it doesn't work like that. the '40'or '60'is a percentage of the wheel width, not a mm figure.

Shit it sounded good though..Sorry,I may have been led astray and spread the disease

;1195823']Largest size is a VRX 17" so cant be more then 15mm bigger in overall rolling diameter.

Actually, the largest OD tyre/ wheel combo was the 16"s. (About 6mm more.)




mate it doesn't work like that. the '40'or '60'is a percentage of the wheel width, not a mm figure.

It's the % of the tyre width, not the wheel.

do a search... it's been covered hundreds of times before.

almost any size rim can be legally put on a magna. you may have to get them certified by an engineer and recalibrate your speedo (not that hard to do, just more expense).

the biggest problem is change in track (measure of the distance between the centre of the tyre treads). you CANNOT change the track of a vehicle by more than 25mm. an engineer will NOT certify track that has been changed by more than that.

This stuff is confusing for a lot of people so don't worry if you don't understand yet.

I'll throw in my bit and try and help too.

Last time I checked, the legal requirement was that the rolling diameter of the tyre can only be + or - 15mm to the largest and smallest tyre fitted to the actual car, as identified on the tyre placard attached to your car.
And as already mentioned, that's the diameter of the TYRE, the rim they don't care about in the slightest regarding diameter.

In my car, the tyre placard says:
http://i18.photobucket.com/albums/b129/Ogier/Magna/IMG_0205-TyrePlacard.jpg

So I'm limited to the diameter of 215/60/16 tyres, plus or minus 15mm.
On paper this is 215x60% for the profile at the top of the tyre, plus that again for the profile at the bottom of the tyre, plus 16" for the wheel diameter. I say on paper (or mathematically) because the actual tyre from the manufacturer can easily vary by many mm.

my maths is (215x0.6x2)+(16x25.4) = 664.4mm is the overall tyre diameter for my car.
(I simplify the first bit to 215x1.2 as that's easy to do in my head)

If I want 20" rims, then these take up 20x25.4mm(508mm) leaving 156.4mm for total tyre height or half that for tyre profile = 78.2mm

As a guideline, for every 1" increase in wheel diameter, take of 5% from the tyre profile providing you keep the same tyre width. 16" to 20" = 4" increase, so reduce the "60" % of my tyre profile by 20% = 40
So the guestimate is that a 215/40/20 tyre will fit.
The maths = 215x0.8+20x25.4 = 680mm that's 13.6mm Larger than my tyre placard, so just scrapes in legally.
I can also try 215/35/20 tyres = 215x0.7+20x25.4 = 658.5 . That's well within 15mm of my original 664.4 mm tyre diameter so less likely to ever be an issue.

So my AWD Magna can run 20" rims with 215/35/20 tyres. 225/35/20 is an even better match and 235/25/20 is good to, so it depends on what sizes the tyre manufacturers actually make and how much they are, but you generally have a few choices.

There are separate laws about rim width that you have to consider.
Typically it says that you can only go 1" wider than what is available for that car, in my case 7" is the max on my tyre placard so I should be able to go to 8" rims.

But I think there's also a rule that says that 8" is the widest allowed on ANY car unless otherwise stated on the tyre placard, and then that size is the max (eg: if a HSV has 9" wide rims, then legally they can only go to 9" wide).

Best bet is to check the vic roads website for the right information. Each state has their regs available online.
For NSW RTA it's VISI 09 in some technical section of registration.
I've cheked most states in the past and have them saved to my HD, but I keep getting caught spouting out of date information, so please check on-line for your state's latest details.

Cheers! Graham.

p.s. I hope that helped explain rather than confusing anyone.

On from what Wookie said - track is affected by wheel widths and offsets - that's a whole different kettle of fish that I'm yet to understand well enough.

So put simply, no its not illegal, as long as you've got the right tyre on the bigger wheels. 235/40R18's are your closest match (2.3mm small roller diameter), then just make sure the new tyres meet or exceed the speed and load ratings on your cars tyre placard and your right.

you can increase the width by more than 25mm (1"), so long as you get an engineer to certify them. there's at least two magnas I know of running 9.5" rims. but then you really have to watch the offset for clearance and track change.

Actually, the largest OD tyre/ wheel combo was the 16"s. (About 6mm more.)





It's the % of the tyre width, not the wheel.

yeah thats what i meant