Tyre size; you can go 50mm above the biggest tyres in your model range

The question of ‘how much bigger tyres can I fit’ on your 4WD comes up regularly, and one of the most overlooked pieces of information is what the law is, and what the consequences are of running a vehicle that has tyres bigger than they are allowed to be.

VSB 14 states that you can increase the tyre size by 50mm. What it doesn’t make clear though, is that in some cases you can actually go more than this.

Here’s the exact wording “Must not be more than 50mm larger or 26mm smaller than that of any tyre designated by the vehicle manufacturer for that vehicle.

What this refers to is simple; its any model vehicle in your range. You should be able to compare tyres sizes for the base model, middle models and top of the range models and go 50mm bigger than the largest tyre in that year range.

If you are wanting to change tyre sizes, please have a read of this first – Fitting bigger tyres to your 4WD; what you need to know.

Tyre wear
How much bigger tyre can you go?

How can you fit bigger tyres?

You are allowed to go 50mm bigger than the largest tyres found in your model range. For example, if we look at our Isuzu Dmax, it came with 245/70/16 tyres, which are 749.4mm in diameter.

For more information on Dmax tyre size options from the factory, look at your tyre placard on the A pillar. Whilst I wasn’t going for the biggest tyres on our Dmax, I wanted the next common size up.

Tyre placard Dmax
The placard on our Dmax, showing the factory tyre size

If you want a tyre size calculator, check this out –  https://www.exploroz.com/Vehicle/Tyres/SizeCalc.aspx

Most people would naturally think that the maximum tyre size is 799.4mm. However, the LSU (a fancier model) came out with 255/65/17 tyres, which are 763.3mm.

Providing the changes between the models are purely cosmetic (chrome bits, fancy dashboards etc) you can go 50mm bigger than the biggest tyres in your model range.

This means the maximum size is actually 813.3mm. This is perfect for us, as a 265/75/16 (one of the most popular tyre sizes around) is 803.9mm.

This exceeds the 50mm increase for the SX versions, but is within the 50mm increase for the LSU versions, and as a result we’ve gone for them.

At 54.5mm bigger in diameter than the stock tyres they are a fair increase, but they actually correct the speedo and give us about 25mm more clearance everywhere under the vehicle.

Now, I want to clarify the cosmetic comment; if there are changes to the driveline, suspension, brakes or anything else between models then this will not apply, as the engineering is different.

Having chrome door handles and a nicer stereo though, is not going to change the way your vehicle handles on the road (and this is what it refers to).

You can’t compare a Ford Ranger Raptor to a Ford Ranger for example, as they are not the same vehicle by a long shot.

Isuzu Dmax
Make sure you are comparing models with only cosmetic differences

For a random fact, the Dmax wheel offset is positive 33mm. If you want more information like this, including the Dmax tyre size for different models head over to Redbook and look through the different models – SX, LSM, LSU etc.

Now, bigger tyres on your 4WD are good in many ways, but like everything, have a number of downsides to 4WD modifications. Don’t forget about them when it comes to fitting them to your 4WD.

Isuzu Dmax with bigger tyres
Our Dmax with 265/75/16’s

What if you want to go bigger?

If you want to go to larger tyres (like 33 inch tyres on a Dmax) then it will be illegal straight off the bat, unless you get engineering paperwork to back it up.

This can be as simple as getting an engineer to sign it off, but more than likely you’ll have to do lane change tests and lots of mucking around.

4WD tyres
If you want to go even bigger, you’ll need engineering

Check with your local authorities

Please, before you fit bigger tyres, give your local road authority a call, and ask them the question. Stick within the regulations and you’ll be much better off!

Is your 4WD legal? If not, you can be in hot water really, really quickly. 

If you aren’t sure of what’s legal, have a read of this; 32 ways to make your 4WD illegal.

Silverado 4WD
Bigger 4WD’s come with bigger tyres straight off the bat

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  1. Hi Adam,

    The models need to be the same in terms of chassis, brakes, suspension etc, with only cosmetic differences (like a nicer dashboard, carpet instead of vinyl or chrome mirrors etc). The Raptor runs vastly different suspension etc and therefore would not be able to be used for tyre sizes on a normal Ford Ranger

    All the best

  2. Adam Hunt says:

    The comment 50 mm larger tyre size can we use the raptors tyre size cause it’s in the ford ranger model range was wondering if I can legally put 275/70/18 on a standard wildtrak it’s 53 mm bigger than standard but not compared to 285/70/17 thank you

  3. Hey Tao,

    I think you’ll have to go to the source, like I did with the Department of Transport in WA. I specifically asked, and got an email about it.

    If you aren’t in WA though, it may not be the same, so go to your local transport department with a specific question, and go from there.

    If you are in WA, and your comments about tyre sizes are correct, you should be fine to go, as you are not doing anything different from a workmate with 50mm bigger tyres

    All the best

  4. I have been searching all the articles from the gov sites regarding tyre size increase.
    All I can find is the 50mm increase.
    I couldn’t find anything about cosmetic difference. If you can share that, it would be much appreciated.

    I’ve got a landcruiser 79 GXL that came with 265/70/r17, which is 777mm. If I go with 285/75/17, it would be 833mm, which is 56mm increase.

    However, a landcruiser 79 Workmate came with 225/95/r16, which is 833mm.
    Can I go 50mm on top of that? That would mean I can go with 315/75/r17 legally without re-certification.