Legal aspects of bigger tyres.

[PradoJim Member Find all posts View Profile Close PradoJim]

First of all, I'm new to the forum and have learned a lot from reading various posts in various categories. That Toyota manual is next to useless when it comes to explaining some things.

I've just bought a 2012 three door SX (equivalent to the GXL 5 door I think).

Would like as much ground clearance as I can get legally and without changing diff ratios. Seems that the 265/70 R17 in BFG or similar is about the tallest tyre that won't give problems on stock suspension. The 3.4% increase in diameter shouldn't trouble the transmission I don't think.

But my reading of the latest NSW rules seems to limit tyre size diameter increase to 15 mm. Those tyres are about 26 mm larger.

To keep my insurance company happy, am I going to have to get engineering for that tyre size ? (to have that warm fuzzy feeling of course. I have oversize on another vehicle and it's never failed a rego check and has no certificate)

Anyone with experience in this area ?

[Guest Close Guest]

See here http://www.pradopoint.com/showthread...l=1#post523757

[PradoJim Member Find all posts View Profile Close PradoJim]

Thanks very much for that link to your excellent summary. I'm still a little confused though.

The document in this link in your NSW section of the State by State thread makes no mention of the 7% rule, only the combined wheel/tyre diameter limitation of 15 mm (which would then require 265/70 R17's to have a certificate). This could be interpreted to only apply if the wheel as well as the tyre has been changed. Perhaps that's what I wasn't getting (?).

This other NSW document linked in your thread clearly mentions the 7% rule on page seven making the change to 265/70's completely legal.

I know what I want to see. Is the section in the second document "more valid" as it is specifically about tyres (and therefore makes the change to 265/70 on the 17" wheel legal) ?

[Guest Close Guest]

Best to call RMS and check with them. Don't blame me when your insurance reject your claim based on information on an internet forum.

[PradoJim Member Find all posts View Profile Close PradoJim]

But amts told me officer ! ; )

You're thread was very useful but I take your point. Will do and report back if I can get an answer.

[PradoJim Member Find all posts View Profile Close PradoJim]

RMS comment

I finally spoke to the RMS technical division about increasing tyre size. They had an email enquiry service but my question was bounced back as the address was no longer valid.

The technician spoke at a million miles an hour, very hard to take notes, but he did so with total confidence. The two documents that I refer to that AMTS pointed me towards are VSI 9 (2003) and VSI 6 (2013).

VSI 9 refers to a maximum wheel and/or tyre diameter increase of 15mm.

VSI 6 refers to a maximum tyre diameter increase of 7%.

The great news is that as far as tyres go, VSI 6 supersedes VSI 9 but only with regard to wheel and tyre diameter increase. That's the bottom line. He went on rapid fire about problems with different descriptions of tyre size increase, Bulletin 14 something or other but unequivocally, you can legally increase your total wheel/tyre combination by up to 7% in diameter.

This would make a 265/75 R17 tyre on a 150 series Prado legal giving you a 53 mm diameter increase (26.5 mm more ground clearance) and squeaks in at just under the limit in percentage- 6.8% (if you've got 17" tyres to start with).

I believe from reading the forum that 265/70 R is the largest 17" without any significant rubbing issues but I guess a small amount of lift may allow the 75's. The only thing left is the effect on gearing.

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I believe from reading the forum that 265/70 is the largest without any significant rubbing issues but I guess a small amount of lift may allow the 75's. The only thing left is the effect on gearing.

The lift usually isn't the issue but usually it's the rubbing on the mudflaps and the chassis.
265/75R17 would be a great size with no need for suspension mods like new UCAs for lesser offset rims. It's just that the size isn't very common compared to a 285/70R17, but in order to fit 285, you will need different offset rims.

There will be a loss in performance with bigger tyres and you will most likely need a speedo calibration device fitted. And don't forget the legalities for total lift. I reckon 265/70R17 is a good compromise.

[PradoJim Member Find all posts View Profile Close PradoJim]

Ah yes, total lift. Thank you. The Prado is a bit shy on ground clearance, that's all, but trying to do all my research before I start doing anything. At least the SWB helps to some degree. Unless I'm going to spend a lot of money with diff ratios etc, I think you're right, the 265/70 is probably a good compromise that won't stress the engine/gearing combo and will give me a bit over 13 mm extra ground clearance. They will also correct the speedo almost perfectly as it currently overreads by just under 4% at 100 kph.

Re performance, I also have a Suzuki Jimny modified just enough to make it very capable. The biggest change in fuel consumption came from bigger tyres. 205/70 stock, 215/75 upgrade. Only 10 mm wider and 5% greater diameter but at least a 10% increase in fuel consumption even when factoring in the altered odometer readings. Not to mention the little 1300 can only just cope with the taller gearing. Absolutely worth it off road though.

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You'll notice a substantial change in fuel economy in the prado too with the 265/70 going on. Its a little more sluggish off the lights and on hills but its negotiable. Speedo will possibly be out too, Mine reads 97 when Im doing 100 in real life.. So be aware of that as well.
At 110 indicated I'm doing 114.5

[PradoJim Member Find all posts View Profile Close PradoJim]

Okay, that's very interesting. Given that it's only a 3.4 % increase in diameter, I wouldn't have imagined much change. Glad to hear it as it means that a jump to 265/75 (if you could get them) would almost certainly be too much without altering diff ratios.

[DGW Senior Member Find all posts View Profile Close DGW]

On my 150 running that size, the speedo was more accurate after fitting and this was verified by an engineer well before VSI 6 came into effect. Yes you will use more fuel and may notice a drop in performance.

[nigelh Member Find all posts View Profile Close nigelh]

maybe try 275/65/17... Only 10 mm change or less going my the OD MM

[PradoJim Member Find all posts View Profile Close PradoJim]

maybe try 275/65/17... Only 10 mm change or less going my the OD MM

Yes, it's only a small change, around 1.7%. I've found that going wider definitely uses more fuel though and for only 10 mm, ie 5 mm extra ground clearance, it may not be worth it. I'm surprised at how noticeable you guys are saying the 265/70 is. It's definitely been worth asking for experiences. It's really making me wonder about the effect on towing.

If I want the ground clearance that bad and given what you guys are saying, then maybe I should accept that I need to look at the whole package to do it properly. Go for the tallest tyre within reason and change the diff ratios.

[Grumpy Junior Member Find all posts View Profile Close Grumpy]

Changing to 265/70 on my 150 average fuel consumption increased by 0.3-0.5 L/100(measured over 15000k's) so nothing dramatic. Speedo reads equivalent to gps. Changing muffler to hi flow made up for slight noticeable power difference in take off.

[PradoJim Member Find all posts View Profile Close PradoJim]

Changing to 265/70 on my 150 average fuel consumption increased by 0.3-0.5 L/100(measured over 15000k's) so nothing dramatic. Speedo reads equivalent to gps. Changing muffler to hi flow made up for slight noticeable power difference in take off.

Thanks Grumpy, I like numbers and it gels with what the other guys are saying. That's a reasonable amount, 0.3-0.5 increase in consumption. Ball park around 4 to 5% increase in average fuel consumption depending what you average. I could live with that. And the 13mm increase in ground clearance, to my mind, is worth it.

This is my first auto 4wd and on a reasonably gnarly track yesterday I noticed how the auto "hides" just how hard the engine/gearbox is working. Sure I could climb some pretty steep and crumbly slopes in high range (which I did just to try), but by seat-of-the-pants was telling me that I'd be better in low range. I say this because it's going to be similar with towing. If I try and pull 2 + tonnes with the bigger tyres, I'm sure it will do it but how much heat would be going into the gearbox ?

From what you guys are saying, it sounds like the 265/70 may be the sensible limit for a larger tyre. Anything bigger I should think about diff ratios. Thanks.