Oversized tyres and roadworthiness/insurance

Submitted: Wednesday, May 07, 2008 at 14:12
ThreadID: 57355 Views:9003 Replies:13 FollowUps:15
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I heard a suggestion the other day that oversized tyres or sizes other than factory were considered a vehicle modification and therefore required certification. Obviously to have an uncertified modification is going to affect roadworthiness and your insurance (usually insurance is affected at the most unfortunate time.) Does anyone know the requirements for QLD??
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Reply By: Wizard1 - Wednesday, May 07, 2008 at 14:32

Wednesday, May 07, 2008 at 14:32
Brad, Brad, Brad,

why don't you just ring Queensland Transport and ask them?

Why do people persist in asking questions of road worthiness and legalities on forums?

Just ask the appropriate authorities and get the right answer not opinion or hearsay.

AnswerID: 302493

Follow Up By: Member - Brad G (QLD) - Wednesday, May 07, 2008 at 14:48

Wednesday, May 07, 2008 at 14:48
Wizard1, Wizard1, Wizard1!

So sorry to interupt your day and cause you to waste some of your valuable time on what is obviously such a futile question and so unrelated to this forum.

Have you ever tried ringing QLD transport and obtaining useful information?

I thought the idea of this forum was to share knowledge and experience. I was hoping for some such knowledge and experience on this topic. Your reply has let me down on both counts.

Thank you to the people who have read this thread - had nothing useful to contribute and have therefore not contributed.

I will continue to persist with whatever questions I feel appropriate. That is what I've paid my membership for.

Thanks in advance to those with constructive information!

FollowupID: 568537

Follow Up By: apriti00 - Wednesday, May 07, 2008 at 14:55

Wednesday, May 07, 2008 at 14:55
You must be a very lucky person or know someone and get the correct answers, unfortunately all to often two people can call and get two different answers. I know because it has happened to me more than once. Maybe a better way of helping someone who has asked for help is to guide them.
Cheers Walter
FollowupID: 568543

Follow Up By: Member - Kevin J (QLD) - Wednesday, May 07, 2008 at 15:21

Wednesday, May 07, 2008 at 15:21

I gave up trying to get people at Queensland Transport to provide constructive and/or intelligent answers to questions raised. Most often the response was 'You will have to put your question in writing so it can be referred to the minister"

So I took my questions to the minister through my local MP and the responses received actually provided me with the reason I could not get answers previously.

The ministers reply to the local MP left him shaking his head in total bewilderment.

I am left to wonder why we allow these people walk around without someone holding their hand. And they make decisions!!!

Brad. Suggest you contact your insurance coy but I believe that
oversize tyres could prove expensive in the event of an accident.
Not sure that you can apply for recertification for tyres.

Kevin J
FollowupID: 568549

Reply By: JustT - Wednesday, May 07, 2008 at 15:09

Wednesday, May 07, 2008 at 15:09
Quoting from:


"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."

AnswerID: 302498

Follow Up By: Member - Brad G (QLD) - Wednesday, May 07, 2008 at 15:31

Wednesday, May 07, 2008 at 15:31
Thanks JustT

That is a good link - saved to my desktop.

Will talk to an engineer i think.
FollowupID: 568554

Follow Up By: Member - Hairs (NSW) - Wednesday, May 07, 2008 at 16:33

Wednesday, May 07, 2008 at 16:33
cheers Just T,
That is a good link.
Wonder if the RTA in New South as a similar one/.

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Follow Up By: pt_nomad - Wednesday, May 07, 2008 at 19:31

Wednesday, May 07, 2008 at 19:31
Its a great link, but I'm not so sure that those figures apply, as they are under the section 'Low profile tyres'. Having said that they don't seem to talk about increasing the tyre size.
A mate who recently puchased a low lux said the rules (in nsw anyway) were dependant on when the car was made. He said that till recent days 50mm was OK and post, 50mm was to big.
FollowupID: 568623

Reply By: Von Helga - Wednesday, May 07, 2008 at 15:17

Wednesday, May 07, 2008 at 15:17
I'm with you on the use of the forums.
If you go the Queensland Transport website and search for "vehicle modification" heaven knows what you will find.
The tyre placard on the vehicle should also be adhered too as well so as you don't put me at risk on the road by going beyond what the designers meant for the vehicle.

Von Helga
AnswerID: 302501

Reply By: Member - Roscoe ET (QLD) - Wednesday, May 07, 2008 at 15:19

Wednesday, May 07, 2008 at 15:19

I'm not sure about how it would effect roadworthiness I would have thought that would relate to safety issues like defective brakes, and tyres that are not legal in terms of tread depth.

In relation to insurance check your policy most of them will have a definition for what a modification is.

In terms of warranty, if the vehicle is still in warranty, you need to read the vehicle's operation manual which should spell it out. I am aware of a situation where a fellow put on oversize tyres, 245 70 R17 when the manual stated the size was 245 65 R17.

Sure there might not be a lot of difference in terms of circumference but what you need to be aware of is the tyres stipulated by the manufacturer are matched to the engine, gearbox and drive train. By increasing the circumference it does have a effect on these, for example the speed at certain revs will be different.

Anyway this fellow was towing a 20' van and busted the tailshaft and a uni joint. As I understand it from what he told me the manufacturer refused to replace under warranty and he had to foot the bill, like $3,000.00.

People do it, raise vehicles, put in chips, oversize tyres and most of the time not a problem BUT when there's an issue insurers and manufacturers will sometimes look for outs.

So I think people need to weight up the risk and whether they want to take it.
AnswerID: 302502

Reply By: Rock Ape - Wednesday, May 07, 2008 at 15:23

Wednesday, May 07, 2008 at 15:23
Brad, I was just going to send the link but then noticed it had been posted.

From my point of view good on you for asking and you have received exactly what you required.

Maybe this is a sewing forum and you are only allowed to ask questions that some others approve of.

The Ape
Sitting here sipping rum and pondering why the hell I have to go back to work tomorrow

AnswerID: 302503

Reply By: traveller2 - Wednesday, May 07, 2008 at 15:24

Wednesday, May 07, 2008 at 15:24
The biggie with increasing tyre diameters is the affect on braking.
While we all realise that a taller tyre will cause the vehicle to accelerate slower it will also degrade the braking performance to the same degree and degrade it further if the tyres are wider due to gearing and rolling resistance.
AnswerID: 302504

Reply By: Shaker - Wednesday, May 07, 2008 at 15:33

Wednesday, May 07, 2008 at 15:33
Isn't the answer on the vehicle's tyre placard?
AnswerID: 302505

Reply By: Member - Doug T (FNQ) - Wednesday, May 07, 2008 at 16:01

Wednesday, May 07, 2008 at 16:01
Brad, Brad, Brad,Brad, Brad, Brad,Brad, Brad, Brad,Brad, Brad, Brad,Brad, Brad, Brad,Brad, Brad, Brad,

Why not check out QT on the website, easy uh .would you like someone to read it for you.

Light vehicle modifications

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AnswerID: 302507

Follow Up By: Member - Brad G (QLD) - Wednesday, May 07, 2008 at 16:32

Wednesday, May 07, 2008 at 16:32
This link was posted on this thread some time ago. I can read the particular post out for you if you like.

FollowupID: 568570

Follow Up By: Member - Brad G (QLD) - Wednesday, May 07, 2008 at 16:41

Wednesday, May 07, 2008 at 16:41
Do people usually cop this much crap for asking a fairly straight forward question??

Are there this many people with nothing better to do than chastise people for trying to gather information?

It must be nice to know everything and not have to ask others for advice, thats what this forum is for isn't it?

OK So I'm not some kind of internet nerd or expert on all things 4wd. Thats why I'm here.

Thank you to the guys who have helped me out. It is much appreciated. It was mostly a simple and painless process.

To the others - get a life.
FollowupID: 568575

Follow Up By: Member - Roscoe ET (QLD) - Wednesday, May 07, 2008 at 18:14

Wednesday, May 07, 2008 at 18:14
Brad G,

You're right that's what this forum is all about and I would say that the fact of the matter is that of the 277 views so far a vast majority of those people have found it informative.

So don't be discouraged keep posting when you want an issue discussed.
FollowupID: 568600

Follow Up By: Member - Doug T (FNQ) - Wednesday, May 07, 2008 at 20:25

Wednesday, May 07, 2008 at 20:25
Don't take things too serious , what might seem like people copping crap for asking a fairly straight forward question is in my case done in jest , so chin up old mate and enjoy .......the flak.
You'll get the hang of it as time wears on, now I didn't know the link had been posted before , sometimes it is a good thing to re-post things because there will be new Members or just visitors to the site that would have missed it , you offered to read it to me , do you want my phone number ,

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Follow Up By: Kev & Darkie - Wednesday, May 07, 2008 at 20:31

Wednesday, May 07, 2008 at 20:31
That would be a great bedtime story for the kids hey Doug LMAO

Cheers Kev
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Reply By: bushy04 - Wednesday, May 07, 2008 at 16:29

Wednesday, May 07, 2008 at 16:29
Brad I had an incident with the RACV several years ago who after I told them that I had oversize tyres on my Toyo when a friend told me to ring them.
I rang only to find that my vechile was not insured and the did not even bother to tell me for six months.
Was a tad peeved and demanded my money back, which after several arguments I got, so be warned.

AnswerID: 302513

Follow Up By: Member - Brad G (QLD) - Wednesday, May 07, 2008 at 16:42

Wednesday, May 07, 2008 at 16:42
Cheers Bushy, exactly what I want to avoid. will do some further research.

FollowupID: 568576

Reply By: Vivid Adventures - Wednesday, May 07, 2008 at 17:25

Wednesday, May 07, 2008 at 17:25
This subject gets a lot of people hot under the collar.

Firstly every state has different regulations and different approaches to policing it. In most states it is not policed at all, and even rarely at roadworthiness checks.

There is a new common vehicle modifications regulation that is in the process of being adopted by all states which is more lenient, and perhaps more sensible.

Small variations have effects on:
* braking (as has been said, but probably only marginally)
* gearing (or effectively reduction in power)
* centre of gravity (usually tyres cause a lot less change in this than changes in suspension)
* speedo (larger wheels mean your speedo under-reads the speed)

My insurance policy specifies the non-standard tyres that are on the vehicle. My insurer (QBE) is happy with this. I have made a claim and had no issues with the tyres.

My vehicle has been in for inspections and the tyres have never been quizzed.

I have never been pulled over by the police, but neither have they pulled me over for non-standard tyres - even in Qld!

My reading of the situation is that small changes 5-10% increases in circumference are barely noticed, and never questioned.

Try jackling your car up with 6" lift, 35" fats, super-charging, etc... and everyone starts to think, "Oh, this might be a problem", or worse, "Oh, the reason he had this accident might have been contributed to by his mods". Then you have a real problem.

In Qld I would get friendly with your roadworthiness inspector and discuss your plans. Then tell your insurance co what you're doing, and it will probably all be fine.
AnswerID: 302520

Reply By: Member - Oldplodder (QLD) - Wednesday, May 07, 2008 at 20:55

Wednesday, May 07, 2008 at 20:55
Agree with what has been generally said.

more than 15mm is oversize .

So to change from 29" OD 235/75/15 to 32" OD 235/85/16, I went to my local mechanic who can blue plates for minor mods, and he agreed to give me a blue plate for the change.

So what is so hard about that ?

Brad, ask around and you may find some local mechanic who can issue a modification plate.

My argument was:
1. The GLS in my year has 31" OD tyres, so not a lot more load on braking.
2. I stuck to 235 wide, so wider tyres not an issue with track.

Also got the speed rating altered to allow for N rated tyres, instead of the Mitsubishi Q rating,

The regs state that more than 10% difference, a speedo check is required. So didn't need to adjust the speedo.

Cost me about $90.00 to do, and stay legal.
AnswerID: 302562

Follow Up By: Member - Brad G (QLD) - Thursday, May 08, 2008 at 07:28

Thursday, May 08, 2008 at 07:28
Excellant info - Thanks John. Maybe tyre fitters can issue a mod plate as well - you would think they would be doing this all the time.

Thanks again, Brad.
FollowupID: 568710

Follow Up By: Member - Oldplodder (QLD) - Thursday, May 08, 2008 at 08:33

Thursday, May 08, 2008 at 08:33
Brad, interesting isn't it.

A few rant and rave, but not many go out and find the solution, and it only took a few phone calls and a little research on the web. I started with a question like yours on a forum.

Mechanic also suggested some slightly softer pads to increase the braking capacity. After fitting, we could still lock up the front wheels so every one was happy.

The reason I went for N speed rated tyres is that it gave me a larger range of tyres to choose from. And the Q rating was for the petrol model, the diesel's top speed is 20km/hr less. The speed rating is for continuous use too, can't see me sitting on over 130km/hr for any sustained period. :o) The first hill would slow me down to less than that even with foot flat to the floor.

Impresses the tyre fitters no end showing them the blue plate, if they ask, but not many actually query putting the oversize tyres on.
FollowupID: 568720

Reply By: Robnicko - Thursday, May 08, 2008 at 08:30

Thursday, May 08, 2008 at 08:30
Having worked in the MV Insurance industry I can tell you that, from an insurance policy point of view, any change to the vehicle from it's standardform that is not disclosed at the time of policy issue is considered a modification. Even if QLD laws allow for 40 inch tyres on the road, you must specify this on your policy. If an engineers cert is required by QLD vehicle registering dept then the insurance company would most likely want a copy of the certificate as well. The co I was associated with insured modified vehicles and would basically insure just about anything as long as the mods were disclosed and had an engineers cert if required by state law. In Victoria I think it's 20mm in height that you can go to before requiring an engineers certificate for tyres and 50mm in suspension lift.............there's lots of people out there paying for insurance that's not valid

AnswerID: 302627

Reply By: zigglemeister - Saturday, May 10, 2008 at 00:55

Saturday, May 10, 2008 at 00:55
Hi Brad,

There are new national standards... Don't ask me how they are applied from state to state, but if you've got the time to wade through it all and find out, have a look at the following link:


I note the following quote from page 16 of that document:

"The overall diameter of any tyre fitted to an off-road passenger vehicle or a commercial vehicle must not be more than 50mm larger or 26mm smaller than that of any tyre designated by the vehicle manufacturer for that model.

Speedometer accuracy must be maintained for the selected tyre and rim combination to within the degree of accuracy specified in ADR18 where applicable."


Tim Z
98 GU Patrol 4500 Petrol/Gas
04 Trackabout Safari camper trailer
91 Holden Nova with a really strange shudder in reverse
AnswerID: 302991

Follow Up By: jpfe8851 - Sunday, May 11, 2008 at 01:20

Sunday, May 11, 2008 at 01:20

Just came across this thread and wondered if someone would refer to the DRAFT National Code of Practice (NCOP).

I have been a contributor to the working party on LS11 in relation to tyres.

Right at the outset, the NCOP is still a draft code and has not been approved in all states but there is a high likelihood the NCOP will be approved and adopted in all states. The drive is to have the NCOP precisely that, a NATIONALLY adopted code so that all states have the same regs so that no longer will vehicle which is legal in one state is not in another.

For you BradG, the NCOP is planned to be adopted in Qld from Jan 1, 2009 and in it's current form has already been approved for tyre sizes for vehicles designed for off-road use to allow an increase of Overall Diameter by 50mm without the need for certification. The problem with this is that the suspension section specifies that the maximum lift without certification is 50mm which can be made up of a combination of suspension lift, body lift or tyre size increase (a 50mm increase in OD results in a 25mm lift in chassis height). So if you changed your suspension to say an OME kit from ARB, you would not be able to increase your tyre size. OME = 50mm lift and a 50mm tyre = 25mm thus 25mm more than the regulation. As many of us already know and do, a popular replacement is the 285/75R16 which is about 40mm bigger than a Landcruiser's OE tyre.

There is a proposal to change the draft NCOP to allow a 75mm lift made up of a combination of up to 50mm suspension and/or body lift plus an increase of the tyre size by 50mm OD (25mm lift). This is still under consideration. The states' transport authorities are concerned that 75mm is higher than they are currently comfortable with in regards to affects on braking, swerve and tilt (centre of gravity). Members of the tyre and 4x4 vehicle aftermarket manufacturers are in discussions on how to provide testing to alleviate these concerns.

All of the anacdotal comments about what people are currently doing would be moot if your insurer abandoned your claim. however the keys to understanding the current situation for 4x4 owners revolve around the applications of ADRs. ADRs overrule state laws in some cases as so long as a vehicle meets ADRs, the federal law takes precedent. And currently there are some anomilies. But I won't detail them here.

But right now and in short you may fit a replacemnent tyre that is up to 15mm taller (or up to 26mm smaller) than the largest or smallest tyre fitted to the vehicle's make, model and series. The key is SERIES as within a series there may be many different tyres fitted to different series within the model. EG a GU patrol may have a 265/70R16 (779mm), 275/70R16 (792mm), 275/65R17 (792mm) but the DX models can be ordered with a 750R16 (810mm). Therefore, even if your GU ST model had say a 265/70R16, you can fit a LT265/75R16 (806mm) because it is well within the maximum size permissable, ie, 825mm (7.50R16 @ 810mm + 15mm = 825mm). This fact is little understood by most tyre retailers and some inspectors too.

The second consideration is Load Index. Replacement tyres must have a Load Index not less than the OE tyre as indicated on the placard. Therefore if your placard states the tyre should 112 LI, then your replacement tyres must be 112 or greater. NOT LESS. If more than one LI is listed you may refer to the lowest LI on the placard. There is one exception. If the placard lists an Axle Rating as in the case of Hilux and several other 4x4 utes, then you may use a Load Index that equates to the axle rating. In the case of Hilux, the axle rating is 1570kg. 1570kg/2 = 785kg = LI of 99. So even though the tyre may be 104 to 112 depending on model, you can replace the original tyre with a lower LI so long as it exceed the axle rating. This is also often not understood.

The final consideration is Speed Rating. This is simple and straight forward. 4WD vehicles require a minimum speed rating of N (140kph) even when higher speed rating OE tyres are fitted but if fitted with a lower speed rating (some vehicles use L) then the lower speed rated tyre may be used. Simple as that. (for cars it is S or 180kph). However, you may want to consider the maximum speed you are likely to drive at and if higher than 140, you should use tyres of a higher speed. But in that case, you are probably well over the gazetted speeds anywhere in Australia, including the new 130 limit in NT, so you've probably got problems with your insurer and the police if driving that fast...!

These last two factors are controlled by ADRs and all states recognise ADRs where they conflict with he literal interpretation of the regualtions as written.

I hope everyone finds this info useful.

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