Welcome to a basic guide to off-road venturing.
Most of us would like to venture into the vast dunes we see on either side of the road, but it can be tricky for the uninitiated to take the first step off the tarmac and into the unknown,
Well the first thing to remember is sand is almost like a liquid surface and our main aim is to stay above it, buoyant if you will and not sink. How do we do that? Lowering the tire pressure. How does that help exactly? It increases the contact patch or footprint of your tires. Which basically means now there is more ground to support the weight of your vehicle and you wont sink in as easily.
At first stick with 15 - 18 psi, going any lower exponentially increases the chances of the bead of your tire losing its seal with the wheel and letting go of all the air (pop out), usually at the worst time and place possible. Once you understand and gain more experience in the art of desert driving you can go lower according to the vehicle and terrain at hand. But in the beginning lets stick to 15 - 18 psi to keep our first steps in to the desert as trouble free as possible.
Now that you have your tires ready for the terrain what do you do now. Full throttle starts are mostly never a good idea but rather gentle acceleration, some situations you need to give it more go than normal, but if starting from a flat and relatively smooth area it is always better to be gentle. Hard starts will usually end up in digging yourself in if not careful. But don't be a granny about it either, remember this is not your typical tarmac surface and gentle blips on the throttle will not get you anywhere. You have to learn to achieve that balance.
Once you get going you have to remember what was mentioned earlier, that think of sand as a liquid surface. You have to keep your momentum, in fact momentum is your biggest friend out in the desert and once you have an intimate relationship with momentum, it will help you out in a lot of places. What you initially thought were impassible tracts of sand, momentum will take you through them.
Think of this as water skiing, once the boat slows downs the skier tends to start going lower and lower into the water until he finally sinks. Although the desert will not consume you and your car like a body of water but getting back to that speed and motion is going to be real hard, and in some places its just not possible to build that momentum again and you will either get bogged down or have to change route.
Don't be afraid to let your engines stretch its legs to keep the momentum going. Most people are afraid to rev their engines too much simply because they are not used to it. Don't change up gears too soon, as the lower rpms will rob the wheels of the required torque to keep the momentum going. But also just don't stick in one gear and let it scream in pain. If you're driving an automatic keep the pedal planted in just enough that it does not shift into the next gear or mashed totally into the carpet that it downshifts and starts to over rev. Automatics in this regards can be a slightly tricky, but they shift gears in milliseconds and keep the downtime in between gears to a minimum. While on a manual you have to be quick and crafty with you changes as too long between gears and you could have broken that fine balance keeping you afloat.
Again taking similarities between water and sand, more like ice in this example. Steering. it will not be as sharp or as responsive as on a hardened surface. The vehicle will not turn on a dime. There is a small delay in where you want the nose to point and where the car itself wants to go. Basically you turn and then you wait for the rest of the car to catch up before it actually starts to and this delay gets worse as the speed of your vehicle increases as well as the softness of sand your driving on. So you have to be a little ahead of time, a sort of a mini time traveler if you wish and be able to predict where you want to be going in the next few seconds rather than waiting for the last moment.
Sometimes no matter of future predicting ability can help you when gravity becomes in charge, this usually happens on slopes and we will talk about this later.
Now that you got your self going, what about stopping? And as always braking, this is different here too, you just can't slam on the breaks. Because all this does is digs your tires into the sand and then trying to move again becomes a hassle if not totally getting stuck. Always gently ease off the throttle and apply the breaks slowly and when ever possible let the car come to a halt on its own. Also makes a big difference where you choose to stop. If your facing uphill and the angle is high enough. 9 out of 10 times you will not be able to carry on forward any further. Always try stopping facing downhill even if it a a very gentle slope. You'd be surprised how well gravity works !
OK, now that we know how to drive on flat surfaces, lets tackle some fun stuff ! Going up a dune ! Sand dunes have two sides to them. One is a gradual climb leading up to what I refer to as the slip face. The other side, a real sharp drop and most of the times there is a nasty bit in the middle of these too. Which I like to call the blade but usually know as the ridge.
At first always try to go up the easy side first. Always look for a smooth and straight line up. Which is clear of all bushes, dips and bumps, basically as smooth a ride up as possible. Then comes the tricky bit. Now what you need is power but in very measured quantity. Too less and you won't make it and too much will send you flying off into the unknown on to the other side.
So to make it simple, the thing to do is give it as much as you got at first but easing it off or totally letting it go before you go flying off. Three Fourth way up the climb you should be able to guess from the forward momentum of the car that whether you need to keep the pedal mashed into the carpet or you need to back off or totally let go and let your old friend momentum take care of the rest with just some gentle blips from you here or there.
Keeping in mind the amount of run up you have had before the climb. If you had enough speed before you hit the dune and specially of it is not a very big one, say twice the height of your car. It would be unwise to mash it as you already had loads of speed and your own inertia will take you over just keep the throttle steady or give it a little more if you feel your losing forward motion on the way up. Sometimes you might even need to slow down if you don't want your bumpers from smashing into the wall of sand.
What do you do once your on the top? Well hopefully your not on your own and you are following someone so keep an eye on that car what it does, goes over, turns to one side etc etc and try to replicate the same thing. If your following someone give it sometime before you attempt the climb yourself, in case there is a problem you cannot see. If there is you should see someone come over the top to tell you or if you have a radio you should get an all clear.
If your by yourself. Always a good idea to go on foot and see whats on the other side. If you don't make it the first time round. Put your car in reverse and slowly come straight down. Sometimes this can be tricky as you may be a bit disorientated from the angle or which way the tires are pointing. Remember gravity and the delayed steering. Gravity will initially pull you down straight and then the delayed steering will come into play and you could end up sideways on a slope. Also never freewheel down, always keep in gear and let engine braking help you down plus this also helps you keep in control of the situation.
Then back up a little further if possible and give it more throttle the next time. Also keep in mind that sand is also a little bit like pie. A hard-ish crust on top with being softer on the inside, and once you drive over a patch you have effectively cracked the crust exposing the softer inner side. So try not to follow your tracks of the previous attempt as you will be treading on the softer exposed sand. The more cars that pass the more churned up and softer it gets. Sometimes it is not possible to get a fresh patch of sand. Only one small exit out of a pocket or only a small crossing on top that is not sharp enough to cross over. In that case try to be on as much undisturbed sand before you are forced to get in line.
As with all things, what goes up must come down. Going down is one of the easier parts of desert driving and sometimes the most scarier parts specially if your a beginner, but don't get too easy about it either. Things can still go wrong. First basic rule is too keep you wheels and the nose of your vehicle pointing straight down. This might be harder than it sounds, remember what was mentioned earlier about reversing down a dune, the same thing can happen while going down nose first. Again never freewheel in neutral down a drop and don't brake too aggressively this will cause your nose to dig in and in a worst case scenario cause you flip over, head over heels. Although this is very rare but this might happen.
Another phenomena while slithering down a dune is fish tailing. That is when the end of your car wants to over take the front, So it starts to come up sideways from behind. What needs to be done is to make the appropriate steering correction and slightly accelerate for your front to get back up to speed with the back. But gently, over enthusiasm here can end up worse than the initial symptom of fish tailing.
If coming down a sharp and steep downward slope engage low 4, 1st gear or D 1 if an auto and then let the car comedown with the help of gravity and engine braking. Better is to start off with less sharper gradients and practice this with being in D 1 or 1st. Once you get used to it you should be able to complete this task in D and just the brakes. But it is always handy to know this technique,
In the end driving in the desert is a delicate balance between momentum, gravity and power and only practicing and driving as often as possible can get you better at it and develop a sixth sense about it. You will learn to interpret the feedback of your vehicle and steering wheel is giving you. You will learn to read the terrain better, even before your vehicle gives up on you, you will realize your not going to make the climb and its better to stop or if you have enough momentum left to come back down. But its better to start of with the correct basics instead of getting ingrained with the incorrect technique right from the start.
This is just a very basic guide covering only some of the points. Remember nothing beats real world practice.
Hope this has been of some help in making that transition from tarmac to sand. Feel free to add or edit or even post questions. I will try my level best with whatever knowledge I have to try to answer your queries.