It is quite common to decrease the air pressure in tires to increase off roads capabilities. By airing down you enlarge the tire footprint...
...the larger the tire the bigger footprint you gain!
When driving on snow and sand it is necessary to reduce the air pressure. On rough gravel tracks it can also be advantageous, because the ride is so much softer and easier for the passengers and the vehicle itself.
It varies between tire brands how effective airing down is. The thinner the tire sides are the more air you can let out. Always keep in mind that the thin sided tires can more easily be cut by sharp stones!
Tire manufactures do not guarantee using their tires with low pressure.
However it is just so much more fun!
Keep in mind that heat is a problem. Rubber wear and tear increases in the heat. This is not a problem when driving on soft snow, but can be an issue on hard snow and hot sand.
Also the danger of the tire falling off the wheel increases. One solution is to glue the tire to the wheel!
During the trip it is highly recommended that you keep an eye on the tire pressure. Because the pressures changes depending on how high you are from sea level and if you are in low- or high-pressure weather.
After you get back on the highway you must pump more air pressure into the tires. You could use a special electrical pump, but air cooling systems can also be converted to be used as air pumps. For the quickest solution, use pressurized CO2 containers.
Air pressure is usually measured in pounds/square inch (psi). The largest tires (38" and 44") can go as low as 3 psi (and even lower in extreme situations). The smaller tires should not have less than 5 or 6 psi.
When driving in such rough conditions it is recommended that you prepare yourself by carrying a tire repair set or even a full size spare tire.
