Driving on Sand
How to drive sand dunes in five easy lessons.
Driving on sand is a really fun way to spend a stress-free day in your Jeep, SUV, pickup, or UTV. With beaches you pretty much only need to maintain momentum to avoid getting stuck. But sand dunes factor all of that in along with other three-dimensional hazards. Outside of an unintentionally hard landing after a jump, encountering hidden objects, or crashing into a "witch's eye" or abrupt sand wall, there's not much that can harm your suspension and axle components like rockcrawling or complex trail riding can. But that's not to say wheeling in the sand is completely without its own set of potential dangers. We've seen it all, from rollovers to wasted suspension components to busted drivetrain parts to shredded tires and everything in between. But if you keep your head and don't drive above your skillset, a weekend out in the sand dunes, cruising the beach, or flying across the desert can be a great way to enjoy yourself.
Lower Your Air Pressure
The goal when driving on sand is to maintain floatation across the surface at all times without allowing your tires to dig. Once you start digging you lose traction and your suspension will start hopping and chattering violently as your tires build and then depose sand under them. This hopping and chattering effect can get so violent that you can actually break driveshaft U-joints, axleshafts, or other parts. Lowering your tires' air pressure in the sand will increase the contact patch to prevent digging. As an added bonus, the lower pressure will also soften the ride and reduce chatter. There's no magic formula to determine your proper air pressure since each vehicle and each tire/wheel combo are different. As an arbitrary example, a Jeep, truck, or SUV of moderate weight may run 35x12.50s at 35 psi on the street, 18-20 psi for light trail duty, and 8-12 psi for rockcrawling. However, for best sand performance you'd ideally be in the 3-7 psi range. Obviously, very low single-digit pressures require beadlock wheels to prevent rolling a tire off the rim bead (especially when turning), so if you're not running beadlocks you may want to err on the side of caution and try your luck at 10 psi. If you're repeatedly throwing beads, then reseat and bump up the pressure or dial back your driving until you reach a happy medium. For the 3,000-pound 1953 Willys flatfender in the photo, Christian Hazel typically runs about 1-3 psi in the sand, 3-5 psi in the rocks, and 25 psi on the street.
Gearing and Throttle to Maintain Steady Momentum
We spend a lot of time enjoying the big sand dunes of Glamis, California, where the dunes are monstrously tall. High-horsepower or super-lightweight buggies notwithstanding, in most cases you won't have enough run-up at the bottom to carry significant speed all the way to the top of some of the bigger dunes like Oldsmobile Hill or China Wall. That means even if you have enough suspension to suck up the rollers at the bottom of the dune to get your rig up to 60 mph, you're most likely going to be struggling to maintain 20 mph at the top. That drastic drop in ground speed brings an equally drastic drop in engine speed, which means you'll be shifting gears at some point on your ascent. And anytime you change gears in the sand you're chancing killing your momentum and winding up stuck. Rather than a full gonzo attack it's often better to ease into the bottom of a dune with the T-case and transmission in a gear that will let you generate respectable tire speed without overrevving or lugging the engine. Get the engine to its happy place with the tires spinning at a good clip and then let the drivetrain and tires do the work. You may not break any land speed records, but more often than not by using this method you'll actually make it to the top. In this photo is Christian Hazel's 1973 Jeep Commando with 33x10.50R15 tires, 3.73 gears, a 2.0:1 Dana 20 T-case, and a TH400 transmission. With only a 150-horsepower AMC 304 V-8 under the hood, Hazel put the T-case in low range and kept the TH400 in second gear to generate sufficient engine and tire speed to get the Jeep to the top of Johnson Valley's steeper set of northern dunes on the way to Claw Hammer's entrance.
Know What's in Front of You
The biggest mistake people make in the sand is to blindly launch off a lip or over the crest of a dune without knowing what's on the other side. The angle of repose for dry sand in most conditions is between 30 and 34 degrees. That means in theory the backside of any sand dune shouldn't be more than 34 degrees steep because that's the typical limit of sand's ability to stick to itself. Anything more than that, and the sand particles will slump down the slip face and create a nice, gentle slope on which you can drive. But that's all theory. In reality we've encountered rock outcrops, scrub brush, saw grass, and any number of other elements on, in, or under sand dunes that cause near-vertical (or even under-vertical) sheer faces that can flat out swallow a vehicle whole. Also, as wind swirls sand, especially around existing vegetation, you can often find conical depressions or big holes euphemistically known as a "witch's eye" that can tear the suspension right out from under your vehicle. Sand is generally a very forgiving medium in which to drive, but it can be equally dangerous, so the best way to keep yourself and your vehicle intact is to drive on it like you would any other unknown terrain. Don't look before you leap.
If you can help it, you never want to stop when climbing a dune slope, especially with your vehicle's nose pointing straight up. If you stop on a steep part of a dune and try to get going again, more times than not your tires will dig and you'll just bury your vehicle. If you are going to abort your climb and need to stop, it's often best to start pulling a gentle U-turn to get your vehicle's nose pointed back toward the bottom. Don't stop until the nose is actually pointing downhill. Aborting your ascent in this manner will prevent you from having to back down a dune, which greatly increases your chance of pitching sideways and rolling. If you do back down a dune, back straight down; don't try to turn around unless you're firmly confident in the stability of your vehicle. If you pull a U-turn to point the nose downslope, keep in mind that by the time you begin your U-turn your speed will most likely have decreased by a significant margin and your vehicle many not want to turn quickly. For these slow-speed U-turns, begin your turn while you still have upward momentum. The vehicle will most likely start crab-walking to the side of your turn before the nose starts following the tires. Stay in the throttle and resist the urge to stop as your vehicle starts pitching down slope. Eventually you'll be at a full sidehill, but stay in the throttle while maintaining your turn, and the nose will eventually pull itself downward and the rest will follow the front bumper. If you panic and hit the brakes before you complete the turn and get the nose pointing down, then reverse will often be your only option and greatly ups your chance of taking a tumble.
Follow the Fall Line
We love off-roading in sand dunes because we also love snow skiing. If you're proficient at one, chances are you'll be proficient at the other because once you get the hang of going with the flow, they're very similar. Driving down sand dunes is all about following the fall lines, and once you master it, it's a pretty zen experience to be out in the middle of a dune sea and gently flow from one peak to the next. As you climb, gently pop over the peaks diagonally at a moderate speed, and you'll keep your tires more or less planted. You'll also allow yourself a chance to scope the terrain and spot hidden dangers, and gain a sense of which way the dune slopes on the back side. Whichever way the sand falls is the way you want to steer down. You can be off the fall line a bit so you're descending a bit diagonally, but for the most part, follow the contours of the slopes on the way down just like you do on the way up, and you'll have a safer, more controlled descent without the big rollover danger compared with trying to steer up off the slope or hitting it at an perpendicular angle.