Hi,
>you can't lower tire pressure to an adequate sand level.
From the perspective of a motor bike pilot this is correct, you will have to drive faster in sand, with higher tyre preassure.
On a 4x4 it is different, rocky ground does not require high tyre pressure. Tyres even becom more vulnerable to cuts using higher preasure ( try out with an inflated baloon and a knife). It is possible to drive with lower pressure on rocky ground, provided that you drive slowly ( < 30 km/h), and have tyres matching the car weight. Pass over steps very slowly. Use tyres with high sidewalls and don't go below about 1.2 bar for mixed terain. The pressure is only a rough figure, it depends on the tyre size and load on the axle.
255/85 R16 with a 4x4 of about 2.7to max is a good match - the lighter, the better.
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Yves
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