Tyre Pressure, ok you need 2 things when 4WD travelling. A tyre pressure guage and a air compressor. When you sort that out you can utilise this information on tyre pressures alot easier.
Think about your tyres as a foot print on the surface, it's easy to see that hard tyres (36 to 50 PSI) will only spread over a minimum amount of surface. They will roll better and also save you on economy.
The reason for softer deflated pressures is when we travel over different terrain. For Example, driving over soft sand, start your pressures at 18 PSI, yes really. When it gets really soft you may even need to run as low as 15 or 12 PSI. On corregated roads in the outback you'll need to find what works best for your car, but maybe try somewhere around 26PSI.
Just remember at low pressure, vigorous turning of the wheel could peel a tyre off, so back off the speed as well. Softer pressure means reduced speed. If you drive on the black top at 18PSI theres a good chance over distace that the side walls of your tyres will heat up and possibly explode. When you get back on the black top, you have to pump your tyres back up. If you dont have a compressor and its5 kms to a service station, go slow 50kmh sort of slow.
Look after your tyres, they are not cheap and they need all the sympathy they can get. Talk to a fellow 4WD owner, a tyre shop or a local aftermarket 4wd store, the more you learn about tyre pressure on different terrain, the better equiped you will be to make the right choice.
This chart will give you a good idea of how the foot print works.