Driving on flat sand is one thing, but what do you do when you’re confronted with huge sand dunes? Here are the best techniques to drive on sand dunes… and to safely get down the other side.
There’s no doubt about it, big sand dunes can be intimidating, no matter whether you’re standing at the base and looking up or you’re at the crest looking down. As with any steep slope, driving on big dunes can present several dangers, but if you set up your vehicle for the task at hand and use the correct techniques you won’t have any problems conquering the seemingly impossible
What are dunes?
Sand dunes are mounds of sand that form as sand particles are blown by the wind into a sheltered area behind an obstacle. As such, they are continually changing in size and shape depending on weather conditions, so even if you think you know a sand dune well, it can be very different from one day to the next.
All dunes have a windward side and a leeward side, the latter often referred to as the slip face. As its name suggests, the windward side is the one that faces the wind, so sand particles are blown up this side. The slip face, which is out of the wind, will be much steeper (32°-34°) than the windward side (10°-15°). It’s for this reason, for example, that it’s easier to drive across the Simpson Desert from west to east, as that’s also the direction of the prevailing wind.
Although desert sand dunes can look very different to beach sand dunes, they have similar characteristics, and the more you understand about them the greater your success rate will be when trying to drive over them.
It’s important to note that you should always avoid driving on vegetated areas in sand dune country. The dunes situated behind beaches act as a form of coastal protection, preventing storm waters from breaking through to the inland during big storms and replenishing the beach when big waves cause erosion. The vegetation aids dune build-up, which also prevents sand from being blown inland.
Sand Dune Features
How hard or soft the surface of a sand dune depends on many factors, including the size of the sand particles, how windy it is, the amount of moisture in the air and if the sand is dry or if it’s wet. It’s also important to note that some areas of a sand dune will offer a significantly harder surface than others.
A damp dune will generally offer a harder driving surface than a bone-dry dune because the sand will have been compacted by the water. And the windward side of the dune will generally offer a harder driving surface than the slip-face, as the leeward side is where the most recent particles of sand have been pushed up and over the crest and deposited by the wind. The softest sand of all is usually at the base of the slip face.
The weather and the time of day will also have an impact on how easy or difficult it is to spot the various features of a sand dune. On sunny days, highlights and shadows can help you to see the contours of the sand dunes, so you can avoid the steepest parts or the softest-looking bits, whereas on overcast days these features can be more difficult to make out.
Vehicle set-up
As with any sand driving, selecting the correct tyre pressures for the conditions is critical to success. If you’re going to be attacking beach dunes, then around 16psi is a good pressure for many vehicles. This will lengthen the tyre footprint and allow it to better float over the surface of the sand rather than cut through it. If you’re fully loaded and driving in the desert, you’ll probably want to keep tyre pressures up to around 25psi.
You’ll need to vary tyre pressures depending on conditions. If the going is difficult, let a bit more air out of the tyres, but bear in mind that you could easily peel a tyre of a rim with low pressures, so avoid abrupt steering inputs and don’t be tempted to skylark when running low pressures.
Despite feeling soft underfoot, you might be surprised just how much damage sand can do to the underside of a vehicle. If the underside of your 4×4 is equipped with little more than plastic splash guards, you’ll really want to avoid hitting the base of sand dunes too quickly. Better still, have your vehicle fitted with some comprehensive under-vehicle protection plates that offer coverage to vital components such as the lower edge of the radiator, the sump, the gearbox and the transfer case.
Finally, if you’re going to tackle sand dunes, you want to be easy to spot, so fit a sand flag to your vehicle. In some parts of Australia, such as the Simpson Desert National Park (now referred to as the Munga-Thirri National Park), the fitment of sand flags is mandatory. It’s also advisable to have your UHF radio set to Scan so you can listen out for other vehicles that are travelling nearby.
Going Up
The key to climbing big dunes is momentum, so firstly you’ll want to select the gear that will give you enough speed so that you won’t sink into the sand but will also allow you to carry enough revs that you won’t have to downshift before you reach the top. Try low-range third or fourth but if you run out of puff have another go in a lower gear, or if you feel the engine is revving too high then try a taller gear. Of course, selecting the right gear won’t be as important for those who drive an automatic 4×4, but it is for those with a manual gearbox, because all momentum can be lost the moment the clutch is disengaged.
Before starting your attempt, study the dune and plot the best route. If the face of the dune is heavily contoured, stick to the high points as these will offer the hardest surface. Where possible, you’ll want a run up, but be careful as you approach the base of the dune, especially if tackling the steeper leeward side, which could see your 4×4 punch into the sand if you’re driving too fast. Once you’re climbing the dune, make sure you keep your speed up.
You’ll want to back off a little as you approach the crest of the dune because you won’t know what’s on the other side. There could be a nice flat area up top, there could be a sudden drop-off or there could be soft depression that could bog your vehicle if you stop. Don’t back off too much, however, or you might not make it over the top.
Always keep your 4×4 pointed straight up the dune; don’t be tempted to turn across the face of the dune as you near the top as this could result in a roll-over.
If you don’t make it up the dune on your first attempt, select reverse and back straight down the dune, ensuring you keep up enough momentum that you won’t get bogged once you’re back down at the bottom.
Before having another crack at the climb, try to figure out what stopped you from reaching the top on the last attempt. Do you need to let more air out of the tyres? Do you need to select a lower gear? Do you need more speed? Or do you simply need to plot another route?
Going Down
With gravity on your side, descending big dunes is easier than climbing them, but there are still several things to be aware of. If you’re descending the windward side of the dune the gradient might not be so extreme, but you’ll still need to keep an eye out for dips and contours, and stick to the higher points where the sand is firmer.
Looking down the leeward slip face from the crest of a big dune can be quite intimidating. The key to safely descending is to ease over the edge in low range first or second gear and then let gravity do the work. The key points to remember are to stay off the brake pedal and keep the vehicle pointing directly down the face of the dune. The soft sand and the vehicle’s low-range gearing will keep your speed in check.
If there’s another dune in front of you, start to accelerate just before you reach the base of the dune you’re currently descending, as the sand between dunes can be very soft and you’ll need momentum to get through. Be careful, however, to check for a drop-offs or step-ups that could cause the front of the vehicle to dig in to the sand if you’re going too fast.
If you get into strife
You’ll need to be armed with the right gear before you tackle sand dunes. You’ll need an air pressure gauge and an air compressor to adjust your tyres to suit the conditions and you should also pack a comprehensive recovery kit.
A long-handle shovel can get your 4×4 out of most situations in sand, but sometimes you might also need recovery tracks or a snatch strap and the help of another vehicle. If you’re travelling solo and you have a winch, you’ll also need some sort of ground anchor.
When using a shovel to clear under a vehicle that’s stuck halfway up a dune, always do so from the high-side of said vehicle. Never, ever dig on the downside of the vehicle, especially if it’s pointing across the dune, because as the sand shifts the vehicle could slide or roll on top of you.
Done and Dusted
Once you’re out of dune country and back on solid ground, don’t forget to reinflate your tyres to normal road pressures. While you’re at it, have a good look at the tyres and check for damage, and examine under the vehicle to make sure nothing is broken, everything is where it should be and rectify if necessary.
Finally, you’ll want to give your vehicle a good wash. Sand is very abrasive and easily can damage paint and other surfaces. Also, sand country means salt will be present, both at the beach and when driving in the desert where there are claypans, so make sure you give the underside of your vehicle a good wash as well.
