technology over sand
Desert driving demands more than just skill and luck – there’s a host of technology to harness

Anyone who has gone dune bashing would know that driving in sand is not an easy thing to do. You need a fairly large dose of off-road driving abilities that will include the knowledge that will get you going up and down dunes with incredible inclines. It also requires a cool head should you be unfortunate enough to get your car's wheels stuck in the sand. This would obviously involve a vehicle with high ground clearance, four wheel drive capability and, for serious forays into the desert, sand tyres. A powered winch could get you out, and a host of other devices would help. The first step, though, is to understand the technologies at your disposal. Knowledge is what will make the difference between enjoying the desert and getting stuck in it.

Four wheel drive
The first thing you will need for driving in sand is a vehicle that has the option of four-wheel drive. As the term implies, in a 4WD the engine powers all the wheels to provide more traction on slippery surfaces. The longitudinal force that helps a car move forward doubles on account of traction coming in from four instead of two wheels. This extra available traction on all four wheels helps the car to move in slippery conditions like sand and snow. This is done by evenly distributing the power generated by the engine through three differentials – front, rear and centre – to the wheels. One of the hazards of a simple 4WD system is that in the rare event of the car skidding it would be harder to recover. As a solution, earlier 4WDs required the two drive shafts to be locked manually before they could be driven on all wheels. Most modern cars have, however, an automated function that allows drivers to shift between 2WD and 4WD modes without needing to stop. Some cars also use a Torsen differential instead of a normal one where the front and the rear drive shafts can be operated with differing amounts of torque. A limited slip differential can also be used that allows both sets of wheels to retain some amount of torque no matter what.

The 4WD and SUV (Sports Utility Vehicle) designates are usually used for vehicles that have a part-time 4WD system that allows the cars to be driven with only two wheels powered on regular tarmac. This is because a car tends to be less fuel-efficient when all its wheels have power being transmitted to them and to reduce unnecessary wear and tear of the differential and tyres. Usually, most 4WDs like the Land Rover Defender or Toyota's LandCruiser operate as cars that are driven by their rear wheels. Once 4WD is engaged the driver can choose between high and low gearing. Most conditions will not require low gearing when the car is receiving power on all wheels. However, some inclines and surfaces require an extra amount of torque where the lower gears can be engaged.

Although the technology used is similar, some cars have a permanent four-wheel drive system in operation. Cars like Subarus and some models of Audi use such systems to enhance the vehicle's handling. The discovery that four powered wheels are better than two came as early as 1966 with the Jensen FF. The next production car to feature permanent drive on all wheels came in 1980 in the form of the Quattro. Thanks to the high level of traction generated, cars with permanent all-wheel drive have been very popular with rally drivers since the Quattro took Hannu Mikkola to the top slot of the World Rally Championships in 1983.

Differentials
When a four-wheeled vehicle is in motion each of its wheels rotate at different speeds because each wheel travels a different distance, especially when the vehicle is turning. This means that when a car takes a turn the wheels on the outside of the car will typically travel more than those on the inside. This inherent behaviour of four wheels travelling together requires that the wheels receive varying inputs from the engine. If all the wheels get the same amount of torque from the engine then one of the tyres would have to slip for the vehicle to turn. The differential is a device that splits the torque and supplies differing amounts of it to the driven wheels to help retain traction and grip.

It uses a system of gears to ensure that the wheels get the maximum amount of torque without causing them to slip. Where the differential is placed depends on what kind of car it is. In a front wheel drive car the differential will be placed on the front axle and connected directly to the transmission case. In a rear wheel drive vehicle a drive shaft connects the transmission to the differential, which sits on the rear axle. In a typical four wheel drive or all wheel drive system there are three differentials. The front and the rear differentials are connected to the third centre differential using separate drive shafts. Usually the two shafts are not locked together and the car moves with only two of its wheels in powered motion. In 4WD mode, however, the shafts are locked – either manually or by an automated system – so that torque is transferred to all wheels.

Winches and towropes
The winch is essential equipment in all vehicles being prepared for a journey into the desert. A winch is a length of powerful wire rope usually attached to the front of a 4WD. Should the car get stuck in the sand you can use the rope and the tow hook attached to it to use any available anchor and pull your car out by coiling the wire in, which also pulls the car out. Winches can be of many types. The most common ones on modern cars are electrically operated and use the battery of the car. Owing to the high consumption of most electric winches most experienced 4WD drivers use an additional deep charge battery to operate the winch, independent of the car's battery.

A simpler and cheaper but perhaps less effective alternative is a towrope, assuming there is a second vehicle around to pull you out. Any accessory shop will give you one for a few rials.

Sand tyres
While the word floatation has no relevance to the world of driving on tarmac, it helps keep a car from getting bogged down in soft sand. Once the tyres sink in the sand they lose traction completely. Floatation prevents this from happening and is achieved by keeping pressure on the ground below the threshold at which the terrain starts deforming. Sand tyres are designed to literally float on the surface without losing traction completely. A good sand tyre is wide, thereby increasing the contact patch between the rubber and the sand – its footprint. This in turn reduces pressure per square centimetre and helps achieve the floatation that is so essential in the sand. Tyres also come with longitudinal grooves and the least amount of transverse tread patterns.

If you have road-going tyres on your 4WD a less ideal alternative is to partially deflate the tyres until the bottom starts ballooning to widen their footprints. Keep in mind however that you will need a compressor to pump the tyres back to the regular pressures before heading back to paved roads.