tyres and saftey

Submitted: Friday, Jan 09, 2004 at 13:35
ThreadID: 9611 Views:1409 Replies:4 FollowUps:7
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Just finished ready the 4X4 Mag and in particular the Ron Moon story with the set up of his rig and noticed that he is running 285/75/R16 size tyres on his partol( also on his web site) and he explains how he has had a Gearmaster trasfer case fitted offset the effects in low range, however he does not explain how he has got over the fact that now his speedo will be out by about 15% and that the brakes on the patrol might not be as good as they were also turning could be affected, and last but not least is it legal also could suffer on hill starts and pulling up hill.
I called a tyre outfit today and asked them if they would fit the same tyres to my patrol and the answer was no way its not legal.
can someone clear this up for me.
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Reply By: Member - Bob - Friday, Jan 09, 2004 at 14:00

Friday, Jan 09, 2004 at 14:00
You would need to have the speedo adjusted/fixed, and then obtain an engineers certificate.Bob
AnswerID: 42352

Reply By: Mark - Friday, Jan 09, 2004 at 14:21

Friday, Jan 09, 2004 at 14:21
I have a GU patrol with 285/75R16 Cooper ST's. I have checked the speedo with my Garmin V GPS and its within 1 km/kr at 100km/hr. The speedo was WAY optimistic with the standard tyres (perhaps thats why others report fuel economy I cannot achieve!!!).

As for braking, I also have ABS and whether the tyre size affects things I do not know. But to my way of thinking, if a 25mm (3.5%) increase in radius is going to make the brakes unsuitable, then they are way marginable in the first place. Overloading the vehicle would make MUCH more difference IMHO. It is rated for 3000kg vehicle AND 750kg tow (unbraked), so there should be plenty in reserve. Theoretically, if 3.5% under the maximum load limit, it should be within spec (perhaps by de-rating maximum load would bigger tyres be acceptable???)

It appears to brake normally, and was told when fitting the tyres that it was fine to do so by Tyrepower. I am not sure about the legality with insurance, perhaps I don't want to know!!! Its insured through my work (novated lease) and bottom line is I do not know the details.


AnswerID: 42354

Reply By: chrisfrd - Friday, Jan 09, 2004 at 14:21

Friday, Jan 09, 2004 at 14:21
4x4 monthly addressed this issue this month!

In fact, the vehicle is not legal, as it is running tyres to which it was not origionally fitted with. (ADR 24!). The only way to comply with the intent of the ruling is to re-engineer the truck completely.

That would be to upgrade the braking system, (probably just change the pads over), and to change the diff ratios to get the speedo reading correctly.

The only way to do this effectively are crown wheel/pinion changes. Look at $1900 for that. That's about the same price as the gearmaster t-case gears!

By the way, Nissan design their speedo systems to read UNDER, typically by 10%, so he would only be out by 5% if everything went to plan.

AnswerID: 42355

Follow Up By: jackablue - Friday, Jan 09, 2004 at 14:49

Friday, Jan 09, 2004 at 14:49

I was told by another GU driver that you can get another tyre standard placard from NIssan for the GU. for a small fee. I haven't questioned him further on it though. Wont be seeing him until Feb.


FollowupID: 304807

Follow Up By: Member - Kevin (NSW/ACT) - Friday, Jan 09, 2004 at 16:17

Friday, Jan 09, 2004 at 16:17
Standard GU placard is for 265/70R16 - you can buy one for a 265/75R16 tyre (same as on utes).


KevinKevin - sitting here, thinking of there
2002 GU Patrol ST 4.2TD
2000 15' Supreme Getaway
FollowupID: 304815

Follow Up By: chrisfrd - Friday, Jan 09, 2004 at 16:23

Friday, Jan 09, 2004 at 16:23

The vehicle ADR compliance details, as recorded by DOTRS (www.dotrs.gov.au) would indicate a truck fitted with such tyres. Not the 285's that Moonie fitted.

If you had an engineers compliance plate, you could change the tyres over to whatever you wanted. I would suggest that there's probably no reason to get booked with 285's on the truck, but if you had a crash and were at odds with the insurance company (as we normally are!) then they could use this as an out with regards to their obligations!

FollowupID: 304817

Follow Up By: Brian - Saturday, Jan 10, 2004 at 11:18

Saturday, Jan 10, 2004 at 11:18
How do you go about this tyre placard?
Do you just buy it or have to get them to certify it to the vehicle?

FollowupID: 304889

Follow Up By: Member - Kevin (NSW/ACT) - Monday, Jan 12, 2004 at 10:05

Monday, Jan 12, 2004 at 10:05
It's a genuine Nissan spare part - Number 99090VB000A - and mine cost $17.40 in February 2003.

CheersKevin - sitting here, thinking of there
2002 GU Patrol ST 4.2TD
2000 15' Supreme Getaway
FollowupID: 305015

Reply By: Eric Experience. - Friday, Jan 09, 2004 at 22:39

Friday, Jan 09, 2004 at 22:39
10 Para.
According to the nissan data the patrol was tested for compliance with 750. 16 tyres, this is the same size as 265 75 .16 , we are allowed 50mm OD over compliance so the 285's are 40mm over compliance, so whats the problem. Eric.
AnswerID: 42414

Follow Up By: Geoff - Saturday, Jan 10, 2004 at 08:06

Saturday, Jan 10, 2004 at 08:06
According to the reg's (Vic), you are allowed 15mm OD over the largest tyre size specified by the vehicle manufacturer for the vehicle model or series.
In the GU Patrol wagons case the largest size offered by the manufacturer is 245/85x16 (owners handbook). The approx OD of this size is 830mm.
285/75x16's are about 835mm OD, which is less than 15mm OD and therefore OK.
The reg's say nothing about the size shown on the compliance plate.
FollowupID: 304867

Follow Up By: Member - Rohan K - Tuesday, Jan 13, 2004 at 17:30

Tuesday, Jan 13, 2004 at 17:30
That's correct Geoff. It is 15 mm. However, it is 15mm more than "the largest wheel/tyre combo" allowable as per the tyre placard. The replacement Nissan tyre placard includes the 265/75/16 that has a theorectical overall diameter of 803.5 mm. Manufacturing tolerances (under most international guidelines) allows a +/1 3.0% variation. Therefore, a 265/75/16 may actually be as large as 827 6 mm in overall diameter. Add to that the allowable 15 mm and you get a maximum of 842.6 mm. The theoretical diameter of a 285/75/16 is only 833.5 mm and is therefore within the specifications allowed.

At least so says the NSW RTA, which has principally the same rules.Smile, you're on ExplorOz
Rohan (Sydney - on the QLD side of the Harbour Bridge)
FollowupID: 305151

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