Most tyre manufacturers recommend tyre pressures for Normal Road Conditions, plus most cars have a sticker showing their recommended tyre pressure. These pressures are for when the tyres are cold, (the pressure increases as the tyre heats-up with driving, up to 6psi).
Off-road you need to adjust your tyre pressure. Lowering the pressure will improve the comfort of the vehicle when you are travelling across rough terrain. Plus it improves how your suspension responds. The lower pressure also puts more tread or rubber on the ground giving you better traction on sand, gravel, mud or steep hills.
This lower pressure is only for low speeds, as soon as you get back on the road ready to drive at normal speeds you must increase the tyre pressure back to the normal range.
So what pressure? How low?
It varies according to the terrain you are about to tackle. If it’s just a rough gravel road on which you intend to travel at a reasonable speed, then 28psi will do the job. But if it’s muddy with big rocks and deep ruts, where you need to go slower then 22psi will be better. This pressure will work for hard-packed sand, but if it’s loose sand that you might find in a dry desert outback then you might need to go as low as 16psi. Don’t go too far as there is a risk of rolling the tyre off its rim at very lower pressures, so drive slow and careful.
If your vehicle has a heavy load then naturally you need to increase the tyre pressure 2 or more psi, than the numbers above, to compensate for the load.
You must re-inflate your tyres before travelling at speed. The best way to deflate your tyres is with a proper tyre deflator and buy a quality 12-volt pump to re-inflate your tyres. You can get both from 4WD off-road shops, it’s worth the money if you are going to get serious about off-road.