Luckily most of us rarely ever have to deal with soft sand. Owners of SUV's using their vehicles recreationally have frequent exposure to sand though. Like when the road has been washed away in a rainstorm and one has to drive on the sand of the dry river bed. As long as the sand is moist, you are safe. Traction and flotation are not an issue.
Only when the sand has dried to a fine consistency and is even difficult to walk on - like on most beaches, will you have a hard time driving on it. 4WD or not.
Stock tires do not provide enough flotation for todays rather heavy vehicles. Theyll cut into the sand like a hot knife in butter. You probably wont get far. The resistance of the sand will soon slow you down to a stop. Small, light 4WD vehicles do best on soft sand. Very light vehicles with very big flotation tires will even drive without trouble in soft sand with 2WD
This is very important for you to remember: When the soft sand slows you down do not increase the gas to maintain your previous speed! Allow your car to work through the sand slowly. It'll speed up by itself once the sand gets firmer. When you notice that one or more tires start spinning (if necessary have someone monitor the tires for you) get off the gas immediately!
Spinning tires will dig deep into the sand and make going back to safe ground very hard. A speedy recovery is almost impossible.
Forget momentum to carry you through soft sand. Using momentum means to be out of control. Youll have almost no steering control. You could hit obstacles hidden in the sand or might smash into trees and bushes.
The only safe and controlled procedure to drive on soft sand is with substantially deflated tires. Depending on your tire size and vehicle weight, drop from your regular tire pressure of about 30 psi down to at least 20 psi - much better for soft sand is 10 psi. Any pointy object pressed into the valve will release the air for you. You should carry a pressure gauge to dial in the correct psi.
Here is why you need to deflate your tires. The tires are now very soft and a large footprint of rubber is in contact with the sand. Drive slowly until you reach firm ground again. Soft sand puts up so much resistance that you may have to use 4WD low range. Always be gentle on the gas to prevent digging in.
If you have a manual transmission shifting up in sand will be almost impossible. So, start in 2nd gear low range and keep it there until you are through.
Automatic owners can enjoy all gears. The automatic is able to shift without any loss of momentum and the torque converter always provides the needed extra torque. However, the hard working engine and the heat generated in the torque converter during this process might lead to overheating. Heat kills automatics. Therefore you may use low range as well.
If you have to drive for several miles on the soft stuff (i.e. up a long desert wash or a long stretch of beach) be extra careful with rocks that might "drift in the sand" like an iceberg showing only the top. Hit one and you risk severe tire damage.
After you are back on firmer ground you should reinflate the tires before driving faster than 30 mph.
Beach driving is a lot of fun. Some stretches of very remote beaches are still open to vehicles.
One more time - why you need to deflate your tires.
Even remote beaches have sometimes vacation homes. Please respect the presence of their owners. Slow down when you see a house on the beach. Kids might be at play. Always drive slowly past any homes.
If you see people present at the beach, drive extremely slow past them. Waive and say Hi. Even better stop and ask: How are you?
Driving on beach sand can be very tricky. Watch for small pieces of wood that were carried up the beach by high tides - they might have nails in them.
Some stretches of beach are tilted down towards to the water. While driving on this tilt you might experience that your rear drifts to the downside. Do not steer to the high side at this point because you will likely loose traction and your rear end will swing to the downhill side even more. The added resistance will also stall your vehicle. Instead steer to the down side, get up to some speed and try to position your vehicle again parallel to the waterline.
Look far ahead. Those tilts might become steeper as you go. So steep that you might not be able to go back up and there might not be enough room to turn around. Youd better have a very good story for your insurance company once you lost your car in the water.
Be aware of rising tides! They come always faster than you think.
Stay at least ten feet away from the waterline. NEVER drive in the water. Rust will render your vehicle useless in a few days. Soft, wet sand close to the waterline could swallow your vehicle.
I will not show you pictures of these incidents. Believe me - they happen very frequently. TV commercials spread the message that it is fun to drive in the shallow ocean water. And I totally agree - its great fun! What they dont tell you is that they throw the vehicle away when they are done filming.
Avoid also driving fast on wet sand. Drive slowly. At speed salty sand would be thrown all over your undercarriage and will cause severe rust even after you rinse the undercarriage with fresh water.
Needless to say on the beach you drive at your own risk.
If you plan to drive frequently on soft sand, consider installing larger wider tires (larger air volume) on your vehicle.