Savvas replied:

Nigel ... You would like to think insurers are consistent in their practices. But we know in reality they are not. Some insurers use contracted assessors to process claims and it seems to be in their interest to find cause to reject claims. Insurers are now using "duty of disclosure" in their policies. If they are not made aware of an issue that could alter their perception of the risk, they can use this to reject claims on the basis that they wouldn't have accepted the risk if they knew of the issue. Safest bet is to inform the insurance company of the tyre issue, get it noted on the policy, get a copy of that notation, and your friend should be safe. The insurance company then does not have a leg to stand on if they reject the claim on the basis of the tyre rating, as they were made aware of it up front and they accepted the risk. This is irrespective of the legality of the tyres. If they note it on the policy, and take the premium, you have a binding contract. The insurance company may try it on, but will back down when challenged with a legal threat, as long as the documented proof is there. Because they know they will lose in court and have to shell out approx $10k in legal fees on top, for both parties.

P.G. (Tas) replied:

Nigel, tell your friend to have a look at Dunlop SP Road Grippers S. These are 8 ply LT (light truck) tyres with an S speed rating (180 kph). They were fitted standard on my 100 series and have given me trouble free running on some of the toughest tracks in the NT and SA. Mine have done over 60,000k's and I will replace them with the same in the near future. Hope this helps.

Rodeoowner replied:

If you get on the Cooper website. it says there that 4wd vehicles only require speed rating N (140km/h) to meet ADR's.

Pete G replied:

Nigel,
RTA NSW website has an article on this point. For 4WD it is Legal to run tyres at 140kph rating as long as load rating, diameter and width fall within the required limits. (if under 140kph then a sticker must be affixed to the windscreen).

I have been through this issue recently with a GU Patrol wagon and found a lack of 4WD tyres rated at 180 kph if looking for other than highway patterns.

Have a look at some AT pattern Bridgestones. I fitted 265/75R16 112S D693's Light Truck. Have done 15k's on them and so far so good. By going to the Light trucks I got a heavier side wall. Compared to the H/Ts they replaced the ride is a little harsher (to be expected) and road noise is the same.

It will pay to verify the situation with your Insurance if fitting tyres outside those allowed on the vehicle placard. However, if they are legal for rego purposes the insurance co would be hard pushed to argue otherwise.

Heat is what damages tyres and heat buildup is a function of load and speed. The tyre rating means the tyre meets a standard to carry a stated load at a stated speed. I am not sure at what temperature the test is conducted but would be surprised if it was any where near Aussie bush temperatures.

One may argue that the general speed limit is only 100kph - fine - and then you load up the wagon and do a run to the NT say Darwin on the bitumen.

Given a long run, high speeds and temperatures whilst fanging along at 160kph with a full load in 40 + deg C heat a tyre blows. One is then up the proverbial creek.

To my way of thinking the 140kph rated tyre is not an optimal tyre in this situation, however the 140kph may be fine for all dirt work where one cannot run that fast.

My 2 bobs worth any way - will probably stimulate some discussion.