Cairns Offroad Training & Tours replied:

I run those tyres on my 80 series at 34lb as recomended by the fitters They have done 30 k so far and still have 9mm of even tread They say the ideal pressure for a tyre is for a 4lb difference between cold pressure and hot Mine go from 34 cold to 37 hot I am happy with that I would try the owners manual recomended setting and if the car steers well at that stick with it Coopers have very strong sidewalls

Cheers Rob Berrill
Cairns Offroad Training & Tours

www.4wdtraining.com
4wdtraining@cairns.net.au

Alex replied:

Jon, if in doubt, follow the manual. Given what you've said about the tyres riding only in the centre, they are definitely way over-inflated at 42psi. The guide I have read in a number of 4wd magazines is to run them for an hour at highway speeds, and then check the pressures again. If the pressure has risen by 4psi they are inflated correctly, if less than 4psi they are over-inflated, if more than 4psi they are underinflated. The correct pressure is obviously very much related to load, when the vehicle is loaded for a trip away, the tyres will need to be harder than when you're just running around town unloaded. I have to admit I've never used this method myself, as I do so many different load trips in a short period of time. I just run at what's placarded on the vehicle, and boost the pressures in the rear tyres if I notice them bagging under a heavier load. I tend to run about 33psi all round, but I'm running a heavier vehicle on smaller tyres (750x16's). However, on long highway trips I have run them all at 50-60psi, so I get there a bit quicker, and on long dirt road trips, such as the Gibb River Road in WA, I run at about 25psi, for better comfort and tyre life. On rough roads, a slightly softer tyre will not only be more comfortable, but will bend around rocks etc, and not puncture/fracture as easily.
I would start out with the pressure recommended in the manual, and work it out from there. the only advantage to harder tyres is a small reduction in fuel consumption due to a lower rolling resistance, but the ride is harder, and tyre wear becomes a lot more uneven. It's generally not worth it. Underinflated tyres also wear unevenly, and may be more prone to blowouts or rolling off the bead.
I realise that this rambles a bit, but in conclusion, lets face it, the tyre shop wants to sell you more tyres, so if they wear out fast through the wrong inflation pressures, they'll get your business again sooner (OK, I'm a cynic). I hope this helps resolve your dilemma. Cheers, Alex.

Alex replied:

Jon, if in doubt, follow the manual. Given what you've said about the tyres riding only in the centre, they are definitely way over-inflated at 42psi. The guide I have read in a number of 4wd magazines is to run them for an hour at highway speeds, and then check the pressures again. If the pressure has risen by 4psi they are inflated correctly, if less than 4psi they are over-inflated, if more than 4psi they are underinflated. The correct pressure is obviously very much related to load, when the vehicle is loaded for a trip away, the tyres will need to be harder than when you're just running around town unloaded. I have to admit I've never used this method myself, as I do so many different load trips in a short period of time. I just run at what's placarded on the vehicle, and boost the pressures in the rear tyres if I notice them bagging under a heavier load. I tend to run about 33psi all round, but I'm running a heavier vehicle on smaller tyres (750x16's). However, on long highway trips I have run them all at 50-60psi, so I get there a bit quicker, and on long dirt road trips, such as the Gibb River Road in WA, I run at about 25psi, for better comfort and tyre life. On rough roads, a slightly softer tyre will not only be more comfortable, but will bend around rocks etc, and not puncture/fracture as easily.
I would start out with the pressure recommended in the manual, and work it out from there. the only advantage to harder tyres is a small reduction in fuel consumption due to a lower rolling resistance, but the ride is harder, and tyre wear becomes a lot more uneven. It's generally not worth it. Underinflated tyres also wear unevenly, and may be more prone to blowouts or rolling off the bead.
I realise that this rambles a bit, but in conclusion, lets face it, the tyre shop wants to sell you more tyres, so if they wear out fast through the wrong inflation pressures, they'll get your business again sooner (OK, I'm a cynic). I hope this helps resolve your dilemma. Cheers, Alex.

Rob replied:

This is an old rule of thumb method to gauge the correct tyre pressure for on road use.

Check the cold tyre pressure & run for at least an hour at highway speed.

Recheck the tyre pressure after the run.

If the reading is 4lb higher you have the correct cold pressure.
If the reading is higher than 4lb the cold pressure was too low & has created too much heat.
If the reading is lower than 4lb the cold pressure was too high.

This can be used for normal vehicle use to various load carrying pressure or towing & also for trailer tyre pressures.

James replied:

What do guys think about nitrogen-filled tyres? Sounds questionable to me. Apparently the tyres don't heat up as much. Then you can't follow that rule.

Mick replied:

Jon: I thought these little black roundies were worth at least 80 Kms... as per their magic guarantees and adverts ! do you expect to get more than that from a set of tyres in the Outback ? I think i know what you are if you think that !!
Are you not supposed to comply with the dealers recommendations as fitted ?

Mick

Guy North replied:

Jon
I had Coopers 6 plies and was unhappy because they chipped badly.
Now I have Coopers 8 plies and they don't chip.
I run on the highway at 32 Psi . In serious 4WDrin=ving grade 3 to 5 to 26 to 28 PSI.
In sand at 20 Psi but our Nissan GU is not overloaded. We don't have a roof rack and usually do about 8000kms per trip.