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Reader help: what are the pros and cons of larger diameter tyres for my Mitsubishi Pajero Sport?

Can a Pajero Sport run larger diameter tyres, and if so, why would you?

QUESTION:

First of all, what a brilliant idea the new website! I used to spend a lot of time fishing for 4×4 content on the Practical Motoring website, now I can have the quality content at very easy access, well done!

Now my question/ask for article:

Much have been said about the issues in increasing the overall diameter of a tyre, but how much is it true, and how much is this impact? Is there any other modification required to minimise any impact, e.g. regearing? I’m looking to replace my tyres to increase the overall diameter by 50mm to stay legal and to improve ground clearance. I have a Pajero Sport 2017.

Thanks

ANSWER:
Thanks for the compliment, and we’re happy to hear you like our new site!

Most Australian road rules now state that you can have a 75mm total lift which usually means 50mm suspension and 50mm tyre – remember that a 50mm increase in tyre diameter is only a 25mm lift. Straight away that lifts your Pajero Sport from 218mm to 243mm, a decent amount of clearance. Because the Pajero Sport has a live rear axle then that’s all the ground clearance improvement you’re going to get, as a suspension lift doesn’t increase ground clearance for live-axled vehicles, only improves approach, ramp and departure angles. Aside from ground clearance the other advantage to larger tyres is a slightly increased ability to clamber over obstacles.

Now to the disadvantages. Larger diameter tyres will increase gearing so all your gears are slightly higher, and engine braking downhill will be reduced. There will also be a fuel consumption penalty and greater stress on the drivetrain due to the increased rolling diameter and weight. Your speedometer probably under-read before by around 5% (indicated 100km/h, actual speed 95km/h) and now that will be reduced or it’ll read accurately. Very large tyres may rub on the chassis or guards at full steering lock or suspension flex.

However, 50mm is a small increase, around 6-7% greater diameter. This isn’t enough for the disadvantages above to be a problem or even that noticeable, but the ground clearance improvement definitely is noticeable and useful. That’s why many people run larger diameter tyres successfully. Don’t go any wider, as there’s no benefit offroad and in fact wider tyres are less effective than narrow ones as the contact patch is the same area, but long and narrow vs short and thick.

While you’re at it, ensure your new tyres are light-truck construction not passenger construction, and make sure you buy five tyres not four, because you will damage your transmission if you put a tyre on that’s a different diameter to all the rest. And ensure the spare tyre can still fit in its original location.

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L901149
L901149
1 month ago

I went for the 275/70R18 Cooper AT3 while lifting my PS Exceed.
Beware, the FCM will have a conniption and go into error, as the car will detect an excessive size tire.

Robert Pepper

Robert Pepper