September 25, 2018
Stay safe and unstuck when riding in the dunes and desert.
By: Jonathan Hanson
Let the Air Out
Letting air out of a tire goes against every instinct we have regarding those critical points of contact between our vehicle and the substrate. But in soft sand street pressure is your enemy, as it concentrates all the weight of the vehicle on four small contact patches. The solution is to spread the load over a larger area, which airing down does by lengthening (more than it widens) the contact patch. Many people assume a tire with a wide cross-section will naturally be better in sand, but at street pressure such a tire might have no larger a footprint than a narrower tire – and in fact the wide tread can be a hindrance as it pushes up more sand in front of it.
How much to air down depends on several factors, especially the weight of the vehicle. Generally speaking, in soft sand with no hazards, such as rock outcroppings that would endanger sidewalls, dropping the tires to 50 percent of street pressure will result in a significant gain in contact area and an increase in the capability of the vehicle that will astound you if you’ve never experienced it.
Experimentation will determine if you need to go (carefully) lower. Drop below 10 psi in a midweight vehicle and you begin to run the risk of popping a bead off the rim unless you are running beadlock wheels. That one-bar mark is a good guide, but do pay attention to the substrate. On one challenging ascent in Egypt – the 1,000-foot-high Dakhla Escarpment – the sand was strewn with sharp limestone outcroppings called kharafish, which forced us to leave pressures higher and subsequently keep speed up more than I preferred. Even so, we shredded one sidewall.
Practice Your Driving Skills
Your driving technique can make the difference between getting stuck and looking like a pro. Soft sand continuously tries to suck the tires in, massively increasing drag and the load on the engine, so RPMs should be kept far enough up in the torque curve to avoid bogging down and stalling. In a manual-transmission vehicle, needed upshifts or downshifts should be performed with alacrity to avoid losing momentum; an automatic transmission smooths out these transitions. All inputs – starting, stopping, and steering – should be gradual. When stopping, you should avoid using the brakes at all if possible; the sand will stop you easily, and braking will only bury the front tires. Likewise, moving off should be accomplished gently, and steering inputs should be deliberate. The vehicle will tend to plow straight forward when turned suddenly, but cranking the wheel more can exacerbate the problem and dig the front tires deeper.
Technology has come to our aid. Land Rover pioneered the user-selectable, computer-controlled driving modes now shared by many vehicles. Sand mode in these vehicles alters shift points, modifies the throttle response, and changes traction-control and even suspension settings to do more or less automatically what we discussed in the previous paragraph. But don’t think merely dialing in that little saguaro icon will make you invulnerable – you still need to pay attention.
Conquering Sand Dunes
What about dunes? It’s possible to drive up the windward side of dunes that look too steep to conquer, and it’s possible to safely descend the leeward, slip-face side of dunes that when you peer over the edge appear insanely precipitous. The mantra: always straight up or straight down; trying to turn diagonally across a dune is a recipe for a roll. If you fail to make it up on your first try, select reverse and back straight down in your tracks without using the brakes. If the vehicle starts to slew sideways, you need to add a bit of throttle and gently correct the steering to straighten it. Likewise, when headed straight down a slip-face, a low gear and the sand itself will retard your forward motion to a surprisingly gentle glissade. If the back end starts to come around, apply throttle and straighten. The trickiest part of dune driving is often at the crest, when insufficient momentum will high-center you on the lip and too much will launch you over the edge.
Keep in mind that environmental conditions can make sand driving more difficult or less difficult. For example, sand tends to be firmer when cool and/or damp, as in the early morning. Your timing when tackling a challenging route can reduce your chances of a bogging.
And what if you find yourself buried and stuck on level sand? An entire treatise could be inserted here, but the second forward motion ceases, get off the throttle. More power will only dig you deeper. The first remedy is simply to select reverse and back up slowly. If the tires spin, evaluate your pressure and reduce if possible. If you’re already as low as you can go, it’s time to use the simple axiom of veteran solo Sahara explorer Tom Sheppard: Lift and pull. Got a buddy with you? A simple tug might be all that’s needed. Traveling solo? You’ll need to get out the shovel and dig ramps for each tire to climb back to the top of the surface. Don’t skimp; a bit more digging now will save you effort in the long run. Next, you’ll need something for the tires to climb on, and few things work better than my preferred traction device: MaxTrax. Although in a pinch many substitutes will work, anything rigid is much, much better than floormats or similar items often mentioned by those who have never actually tried them.
With proper technique and a basic sand kit – a good air compressor, a set of deflators to ease airing down, a shovel, and a set of MaxTrax – you’ll be ready for that expedition to Egypt.