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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.

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.

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.

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, 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

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?

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6 comments… add one
  • susan wilbraham June 6, 2019, 2:54 PM

    so will a 265 x 75 x 16 tyre fit under the front guards of a dmax with out rubbing or what would you recomend

  • Aaron Schubert June 6, 2019, 5:01 PM

    Hi Susan,

    Yes, providing the suspension isn’t sagged


  • Tim July 15, 2019, 7:58 AM

    Hi there,
    I am wondering if you have found any noticeable drawbacks in handling/steering or changes to the way the dmax drives since fitting the new size? Some people comment on power loss.

    I have one with stock 245/70r16’s that need replacement. I am looking at 245/75r16 as the demo I drove with 265 felt heavy in the steering. Any thoughts ?


  • Aaron Schubert July 15, 2019, 8:15 PM

    Hey mate,

    I swap between the tyres a fair bit. I can’t feel any obvious differences, but it does brake worse, get marginally worse economy and you do lose some power and torque. With all the weight, wind resistance and the trailer it is noticeably slower than when I got the vehicle.

    Life is a compromise; I wanted the extra clearance and will put up with the negatives


  • Micheal January 3, 2020, 5:51 PM

    Cool article, but there is something I’m questioning. When you say you can actually fit larger so long as it is within the same model range, what if those tyre sizes from the upgraded models aren’t actually on your tyre placard? I have an amarok trendline that came with 245/70/16 and that is the only size on my door placard. But looking at the amarok ultimate version, it came with 255/55/19. Therefore, a set of 265/70/17 (or similar) would be legal on a 2014 ultimate, but not my 2014 trendline. As far as I can see the changes are only cosmetic and I’d probably need flares.

    So is using any model in the range your interpretation of the rules, or am I missing something completely here? The way I interpret “Must not be more than 50mm larger or 26mm smaller than that of any tyre designated by the vehicle manufacturer for that vehicle”, is “That Vehicle” refers to mine specifically and not others in the same year/range.

    Id love to be proven wrong, as I want to legally run a 265/70/17, but its about 4mm to big for legal purposes. Don’t want to be defected miles from home on a family trip! Or worse yet not have insurance pay out.

    Would you use the same interpretation for wheel offset? The variance in the 2014 Amarok range is nearly 30mm from memory.


  • Aaron Schubert January 3, 2020, 7:16 PM

    Hey Michael,

    You raise an interesting question, and one I have wondered about myself. I would say it has to be in the same year range, and the only changes could be trims, upgraded stereo’s etc, without touching any of the drive line, suspension, brakes etc etc. I don’t know enough about the Amarok’s to comment, but have confirmed my thinking on this is correct with the Department of Transport and a few engineers over here in WA.

    All the best

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