Before going onto individual techniques, it is important to understand the how 4×4 gearboxes work and how tyre pressures affect vehicle performance.
Understanding 4×4 tyre pressures is one of the most important parts of the preparation for driving off-road. Deflating or inflating the vehicle’s tyres, and altering the tyre footprint, makes such a significant difference to a vehicle’s performance, this subject is critical if off-road driving is to be understood, even at the most basic level. It alone can mean that your vehicle will sink and stick, or float and go, slide and crash or grip and go safely. As a result, there are few subjects in the world of 4x4s that are under such constant debate.
Reducing tyre pressures:
• When traction is marginal such as on steep, undulating climbs or tricky, lumpy descents, shallow slippery mud and general off-road driving, tyre pressures should be reduced by ±20% of normal operating pressures.
• To reduce the shock effect of tyre impact when driving over rocks, pressures should be reduced by ±20%.
• To improve comfort, safety and stability on corrugations, pressures should be dropped by 15%-20%. Be careful of dropping pressures too low when carrying a load because low pressures can also result in reduced directional stability and while making things more comfortable, reduced pressures may also cause handling difficulties.
• Likewise, excessively high pressures, set because of a heavy load or trailer, can also adversely effect handling, especially noticeable on gravel corrugations.
• If conditions require protection, such as on sharp rocks and in conditions where the tyre sidewalls are threatened, then I recommend dropping the pressures by as much as 30%. The trouble is, the lower the pressures the wider the sidewall will bulge, thereby making it more vulnerable. But like a balloon, which is easier to pop when fully inflated than when soft, a hard tyre is more vulnerable to damage by rocks than a soft one.
• If conditions require flotation, tyres should be deflated. On sand tracks where speeds are 40-50 kph drop pressures by 15%.
• On sand that is extremely soft, tyre pressures can be dropped to as low as 0.5-bar. HOWEVER, at this pressure, the risk of a tyre coming off the rim is high. Steer cautiously and drive slowly. Some tyres will not permit such a low pressure as the bead design will not keep the tyre on the rim. In this case, 0.8-bar is about as low one can go. Tubed tyres can be reduced to 0.3-bar safely.
• A vehicle with tubed tyres can be driven more aggressively because the tube serves to hold the tyre on the rim and if the bead is broken, there will be no loss of air. For this reason pressures can be dropped lower than with tubeless tyres.
• At any pressure lower than normal, speeds must be kept down to prevent tyre damage, especially if you are using tubed tyres.
• Excessive speed with reduced pressures, with tubed tyres will quickly wreck the tube and a blowout is likely.
To take a more scientific look at why reduced tyre pressure have this effect, click here.
To review this article on video, click the play button below:
SURFACE CONDITIONS – PRESSURE REDUCTION
Sealed surface 100%
Gravel / Corrugations 10 – 15%
Rocks 15 – 20%
Sand 50 – 60%
Emergency tubed – tubeless 0.35 bar. – 0.6 bar.
USING 4WD TRANSMISSIONS
It is safe to say that the majority of 4×4 drivers do not use four-wheel drive as often as they should. There is a misconception that driving in four-wheel drive can damage the transmission. This is true only for driving on dry tarmac in locked-up four-wheel drive, and even then damage is gradual and while it’s happening the driver is warned by an unnatural vibration. Don’t be scared of using four-wheel drive!
Drive to all four wheels should not only be used when in difficulty but to increase tyre adhesion, even if it appears to be adequate. While researching a book in 1994, I was loaned an Isuzu KB260 for a trip into the Maluti Mountains. After the road ahead was blocked by a swollen river I was forced to about turn and head back. It was getting dark and to make matters worse it started to rain. In two-wheel drive the Isuzu handled fine but I wasn’t comfortable because although the surface was firm, occasionally the back would slide out. Then I locked the hubs and engaged four-wheel drive. The Isuzu now drove as if on rails and I felt happy that we were traveling in complete safety. We did not need four-wheel drive but it improved handling so much that we increased our speed from ±50 kph to about 80 kph. Fuel consumption increased marginally and I calculated that for the 60 kilometers we traveled that evening, at a conservative 5% increase in fuel consumption, I spent an extra 92c on fuel! The increase in fuel costs is so small while the increase in safety so huge.
Driving all four wheels offers better all round safety, handling and improved tyre life on anything but a perfect road surface. So my first bit of advice is: Engage 4×4 not because you need it, but because it’s there. And, safety is everything.
When Must Four-Wheel Drive be Engaged?
The key is BE PREPARED. Select four-wheel drive BEFORE you encounter difficulties. If you consider that the terrain over which you are about to travel could not be easily traversed in a normal motor car, then engage four-wheel drive. Even if it is just a rough track and the going is easy, engaging four-wheel drive will reduce wear on the transmission by distributing the pounding to all four wheels instead of just two. If you have free-wheel hubs, lock them immediately you leave the road and you will be able to engage four-wheel drive from inside the cab at a moment’s notice. It is a bit like wearing a seat belt: One does not wait until you need a seat belt before putting it on.
Holding the Steering Wheel
In almost all off-road situations it is not necessary to fight the vehicle, forcing it to change direction. It is far preferable to hold it lightly enough to let the steering wheel slip through your hands should it have to, gently coaxing the vehicle to go in the direction you wish.
Keep your thumbs outside of the steering wheel rim. Steering kickback when hitting an obstacle can jerk the steering wheel around with such force that it can badly bruise a thumb or finger.
In difficult off-road situations, climbing out to inspect the ground over which you are about to drive can prevent bogging down or vehicle damage. This is especially important when negotiating rocky terrain where transmission damage can result if rocks strike the gearbox or axles and expensive body damage can result. I do not subscribe to the opinion that it’s okay for a vehicle designed for off road use to get damaged occasionally.
Avoid Misuse of the Clutch
Engaging the clutch at the wrong moment either to change gear or to prevent a stall can create problems off-road. The beginner should avoid the clutch whenever the vehicle is traversing an obstacle – avoid changing gears and rather let the vehicle stall on a slope than risk a backward slide out of control. Next to hooliganism, misuse of the clutch causes more accidents off-road than anything else.
ENGAGING FOUR-Wheel drive AND LOCKING DIFFERENTIALS
Engage four-wheel drive in conditions where you feel that a two-wheel drive vehicle may spin a wheel and struggle to get through.
Permanent 4WD (Centre Differential Lock)
Lock the centre differential if there is any danger that any of the vehicle’s wheels will lose traction and spin. Also as a safety measure when travelling at high speed on gravel or wet, oil-slick tar. Lock the centre diff whenever low range is engaged, no matter the conditions.
‘Super-Select’ 4WD (Mitsubishi)
Engage four-wheel drive, centre diff unlocked in ALL conditions other than smooth dry tarmac. Locking the centre diff as above.
Rear Axle Differential Lock
Lock the rear axle differential in conditions which are severely undulating, when wheels lift well off the ground.
Many off-road drivers tend to lock the rear diff the moment things become challenging. This robs them of a chance to learn and hone their skills. Just because wheels lift off the ground it doesn’t mean that a rear locker is needed. It just means that a rear locker will make it easier. Try your skills, use the push-pull technique (see axles twisters later in this chapter) and try and get through. If you find it is impossible or you feel that the vehicle is being stressed, go right ahead; stop the vehicle, engage rear diff lock and drive through. I recommend this approach because bad driving techniques are easily masked by a locked rear diff.
In flat soft sand axle diff locks can hinder progress due to the under-steer they cause. This under-steer causes the turn of the front wheels being exaggerated creating a very high rolling resistance of the front wheels, halting progress. Always stop the vehicle before engaging. Failure to do so can wreck the differential.
The Transfer Gearbox
Part of what makes an off-road vehicle special is the transfer gearbox, the second gearbox in which an additional set of gear ratios is available for off-road driving. The transfer gearbox reduces the overall gearing, giving a new set of ratios that are changeable by the gears of the main gearbox. For example, a 5-speed gearbox plus the transfer box provides the vehicle a total of 10 forward gears, and two reverse gears.
Avoid excessive throttle openings when in low-ratio first or second as the high torque loads can destroy differentials and twist off half-shafts. In the case of selectable four-wheel drive vehicles, additional lever/s attached to the transfer gearbox will select four-wheel drive.
Levers on part-time four-wheel drive transmissions:
• Two-wheel drive – high-ratio (normal road driving).
• Four-wheel drive – high-ratio (easy off-road driving and for momentum-critical driving, e.g. sand).
• Four-wheel drive – low-ratio (difficult, slow off-road driving).
Levers on full-time four-wheel drive transmissions:
• Four-wheel drive – high-ratio (normal road driving).
• Four-wheel drive – high-ratio + centre differential lock (easy off-road driving and for momentum-critical driving).
• Four-wheel drive – low-ratio + centre differential lock (difficult off-road driving).
• ABS on/off. (Off-road conditions where engine compression is used to slow the vehicle)
Even for moderate off-road driving it is advisable to lock the centre diff whenever the low-ratios are selected. This will protect the differentials from damage due to excessive torque transmitted when in low-range. The transfer gear lever may have a central position marked “N”. In this neutral position no power goes to either prop-shaft. Neutral is used when the engine is being used to drive auxiliary engine driven equipment via power take-offs. It is also the position which should be selected if the vehicle is being towed.
FREE-WHEEL FRONT HUBS
The sole purpose of free-wheel hubs is to save fuel on the open road. The amount of fuel they save is not measurable under 100 kilometers. Often drivers of part time four-wheel drive vehicles use more fuel than their permanent four-wheel drive counterparts because when the going gets a bit difficult they are often too lazy to stop, get out and lock the hubs and instead battle through in two-wheel drive and use more fuel.
I once did a trip to confirm this. Having driven my Land Cruiser FJ79 from Johannesburg to Cape Town (±1500kms) three times, and had measured its fuel consumption each time, on the fourth drive I left the front wheel hubs locked for the entire way. I anticipated a slight increase in consumption but it turned out less than even I had thought: Approximately 0.2 liters per 100 kms higher than the already established average; an extra three liters for the entire trip.
Driving with the hubs locked does not damage the transmission.
Some think that they must be unlocked when driving on a tar road. This is untrue. I suggest locking them once the long, high-speed tar driving is complete and the gravel and off-road driving lies ahead. In this way the driver will be able to select four-wheel drive from inside the cab. Then, when the trip is over, and you are on the road to go home, unlock them to get any fuel savings that may result.
ELECTRONIC TRACTION-CONTROL (ETC)
Traction control, fitted to many modern 4x4s, is an electronic traction enhancing system developed to improve traction by taking the energy created by tractionless, spinning wheels, converting it into pulling power which is then transmitted to wheels with good traction by use of the ABS brake system or hydraulics. The driving techniques for vehicles with traction control are not the same as for those without.
The fundamental difference in driver technique is in the use of the accelerator. The technique of easing the throttle during wheel spin will cancel out any effect that ETC may be having. In this case ETC might as well not be there. Should the driver keep the throttle open, a well set up ETC will activate, braking the spinning wheels and transmit power to the wheels with traction. Therefore it is safe to say, if you have a vehicle fitted with ETC and a fully-locked up four-wheel drive system, both techniques will work. Of course the beauty of this is that should the first technique fail, try the second. The best of both worlds!
As technology in traction control advances so does the effectiveness of these systems. Some of them, for example the one fitted to the Jeep 2005 Grand Cherokee, is so effective that it is almost impossible to spin a wheel. All four spin, or none at all. The system is so ‘clever’ that it takes much of the fun out of difficult off-road driving.
ELECTRONIC SAFETY DEVICES
Modern 4×4 are endowed with safety features not dreamt of a decade ago. One of the most common has a remarkable effect on off road performance. This is the anti-skid system, sometimes called ESP. It is remarkable how it will correct a slide on corrugations or during a violent swerving action. The first one I drove was fitted to a VW Touareg. Here is what I learnt: When on uneven ground select the suspension height to ‘off-road’ and set the shocks to ‘sport’. This prevents bottoming on big bumps. And, turn off ‘ESP’. With ESP turned on, the Touareg likes to go in a straight line; try and turn and it bogs itself down. Since then I have driven several, one being the Fortuner. It does much the same thing and if left on, in thick sand, quickly bogs the vehicle down immediately the steering is turned. Most ESP systems will switch off when low range is engaged. Check your vehicle’s ESP equivalent and experiment the next time you go out.
When descending or ascending steep slopes follow the fall line. Avoid tackling slopes at an angle as a slide and roll-over could result. Never try to turn around on a slope that is more than 25°.
Descending a steep slope
The trick is to use the compression of the engine to slow the vehicle down. In doing so all four wheels are braked simultaneously. This eliminates, on all but the most severe slopes, the risk of the wheels locking and a slide resulting.
The golden safety rule for driving, either up or down steep slopes, is under no circumstances depress the clutch. The techniques for descending slopes with a firm base and those with a slippery base differ, as follows:
The procedure is as follows:
• Remember the golden rule: if you depress the clutch at the wrong moment you may lose control. No matter what happens, the clutch is not required if the vehicle is moving.
• Engage four-wheel drive, ensure that free-wheel hubs are engaged and lock any differentials that you can lock.
• Select the lowest gear available; low-range first.
• Release the hand-brake and begin the descent.
• As the vehicle begins its descent take your feet off the pedals and place them on the floor. If you’re a beginner you may want to tuck your left leg under the seat to prevent the inadvertent use of the clutch.
• On all but the steepest slopes the engine will provide all the braking you need. You will have full control because there is no chance of locking the wheels due to action on the brakes.
• If the vehicle loses traction and starts to slide, steer towards
the direction of the slide (downhill) and apply gentle, careful acceleration.
• If engine braking is insufficient, gentle application of the brakes can be made. Do this when the vehicle is moving in a straight line. (So brake before a corner and take the corner under compression only)
• Apply brakes in short sharp jabs to avoid locking the wheels (cadence braking). Be aware that the use of brakes can induce a slide, so take care not to cause a wheel to lock.
• If you are using the brakes they must be released the moment a wheel begins to slide or the vehicle’s direction changes due to a slide.
• NEVER change gear during a steep descent without your foot first pressing the brakes. If the clutch is depressed the vehicle will speed down the slope out of control.
• If your engine stalls during the descent because your vehicle has hit an obstacle, start it with the starter motor while in gear and keep your foot well away from the clutch.
• When descending on very slippery ground, the use of the brakes is highly dangerous and can induce a slide from which you may not recover. Low range second is the gear of choice for very slippery descents and descending sand dunes.
• With auto transmissions, use the brakes from the beginning of the slope, control the speed with the brakes and do not let the engine race.
Ascending a steep slope
When confronted with a steep slope to climb the driver must decide: Do I need momentum or control? For example in the case of climbing steep dunes, speed and momentum is the essence whereas climbing a rocky slope, traction is the most important element. A higher gear and speed will provide momentum but if the slope is bumpy this will cause the wheels to bounce, resulting in loss of traction.
The procedure is as follows:
• Engage four-wheel drive, lock the center differential and make sure the free-wheel hubs are engaged.
• Select a gear that will offer enough torque to get you up, but not too low as to promote wheel spin. Second or third gear low-ratio usually works well.
• Select your line. An even, steep slope is better than an axle twister at a flatter angle.
• Do not rush the slope. As the vehicle hits the slope at a too high speed energy is absorbed and the result is a vehicle that begins the slope on the rebound. It is at a disadvantage from the beginning. Rather apply firm accelerator the moment after the front wheels begin the climb, and not before.
• As the vehicle begins its ascent give a little extra power. The more slippery the surface, the more momentum you will need to get over the top. If the surface is uneven, a lower speed will prevent the wheels from bouncing and leaving the ground, thereby losing traction.
• If the vehicle loses traction and wheels start to spin, decelerate very slightly and accelerate again once the wheels grip again.
• Decelerate as you crest the slope to avoid hitting an unseen obstacle or go careering over the edge in the wrong gear.
• If your attempt fails due to lack of power, select a gear one lower than the gear you first tried. If your attempt failed due to loss of traction, you have two choices – select a higher gear than before and/or, drive the slope with a little more speed. Revise and change your line.
• A gear change during the ascent may be needed if not enough momentum can be achieved at the lower section of the slope. A very rapid change down can be attempted but must be done at the place on the slope of minimum traction. E.g. Corrugations.
• With auto transmissions, the technique is the same, although a mid-slope gear-change is possible.
Engine stall on a steep slope
If your engine stalls during a steep ascent the vehicle is in a potentially dangerous situation. The golden rule applies more in this situation than in any other: allow the vehicle to stall and do not try to prevent the stall by depressing the clutch. It is this single act that counts for more off-road accidents than any other.
If your vehicle stalls on a steep slope:
• Apply the hand-brake firmly simultaneously holding the vehicle with the foot brake.
• Depress the clutch , slowly and cautiously. If safe, engage reverse gear and release the clutch.
• If you are unable to engage reverse because the vehicle cannot be held by the brakes alone, have someone pack rocks behind the wheels to secure the vehicle. Once this has been done engage reverse and release the clutch.
• Release the hand-brake – slowly.
• Start the engine, (only kick the starter otherwise the starter motor will propel the vehicle down the slope) while engaged in reverse with your foot off the clutch, while simultaneously gently releasing the foot brake. The engine will fire and the vehicle will descend safely under engine compression braking. From this point the procedure is described in ‘descending slopes’ but this time it is done in reverse.
When a steep slippery mountain track tilts the vehicle the rear wheels often break away causing a slide. On clay-type mud this can happen without any provocation and is severely exaggerated when one is moving down a slope.
This situation is corrected as follows:
• Steer towards the direction of the slide.
• Accelerate gently.
• Do not use brakes as this will increase the slide.
• Once the vehicle is straightened up, cadence braking can be used to slow the vehicle.
• Side slopes on sand are particularly dangerous because of the danger of roll-over as the lower wheels penetrate the sand, increasing the angle. When approaching a slope in thick sand, take it at speed under high power, making sure that momentum is maintained.
A good rule is to walk across the obstacle before you attempt to drive through it. With mud this is rarely done, and this is why four-wheel drive vehicles can easily suffer structural damage while driving in mud. Rocks and logs often lie hidden under the mud and hard mud is often driven through with excessive speed.
Mud driving can be tricky, especially for a vehicle fitted with broad tyres better suited to beach use where the shallow treads quickly clog and sit on the surface without any grip. In most cases mud requires lower than normal tyre pressures.
A few rules can be applied when driving in mud:
• Engage 4WD well before you need it and lock differentials. If you have both front and rear axle diff locks, leave the front disengaged unless the conditions are particularly bad – locking both axles causes steering difficulty. Make sure your free-wheel hubs are engaged.
• Select the appropriate gear before tackling the most difficult terrain. For thick, deep mud in a large engined vehicle, third gear low-ratio is suggested. With smaller engined vehicles, select second gear low-range. The lower the gear, the more chance of wheel spin. The higher the gear the more chance of having to change down a gear, which could mean loss of momentum.
• Avoid doing anything suddenly. Keep your actions smooth and your steering wheel dead ahead if possible.
• There are two techniques to be tried: Even and constant power application. Don’t accelerate when wheel spin occurs and don’t decelerate when the vehicle accelerates. Keep the power application constant. This is often the easiest and most effective technique for beginners.
• Another effective technique is to look for traction. To do this, when wheel spin occurs, decelerate immediately, but delicately.
If you take your foot off the accelerator completely your vehicle will slow down too quickly, and when you accelerate again the wheels are likely to spin. It is a balance of accelerating when traction is good and decelerating when wheel spin occurs while also keeping the speed constant.
• If you find that the wheel spin continues and you are slowing down, it means that you are about to get stuck. If you avoid accelerating and continue to decelerate slowly while your wheels are spinning, and you still get stuck, rest assured that although you may have stopped, you will not be deeply bogged down. You would have avoided making unnecessary work for yourself by spinning your wheels and digging yourself in deeper. In order to assist the tyres get traction from the sidewalls, try swinging the steering wheel from side to side when the vehicle is moving. This works well if the wheels are spinning in ruts and the consistency of the mud is firm.
When driving in thick mud with broad tyres designed for flotation in sand, spinning will not cause them to dig in as quickly as would narrow mud tyres. Instead, the treads clog with mud and the tyre loses all traction and spins on the top of the mud without driving the vehicle. In this case the best course of action is to drive through the mud at speed, keeping the wheels spinning. In the process the mud clogging the treads is flung out. There is a danger in this situation of damaging the vehicle by going too fast and hitting unseen obstacles hidden under the mud.
Steep mountain slopes in slippery mud
Allowing the wheels on one side of the vehicle to drop into a ditch at the side of a track is one of the most frequent ways in which vehicles bog down in muddy conditions. These ditches often occur on both sides of the track and are caused by water run-off that has eroded deep channels that catch the unwary. Unless your vehicle is fitted with differential locks on the axles, the wheels buried in the ditch will spin and the wheels on the outside will remain stationary. So, if you are traveling on a track that slopes away at its edges, drive slowly and carefully stay in the middle.
Descending slopes in shallow, slippery mud:
• Use low gear ratios and go slow. Do not be in a hurry. Lock up four-wheel drive even if you do not think you need it. Conditions change very quickly and if you are engaged in four-wheel drive you stand a better chance of handling them.
• Steering control is lost when the vehicle’s motion exceeds the rotation speed of the wheels. This will occur if you use brakes in the conventional way – so if you need to stop, apply brakes in short, sharp jabs.
This is a method using small wheel rotations (1/4 to 1/2 a wheel turn) to build up momentum when a vehicle is caught between two obstacles. Select low-range second or third gear. Increase the engine revs and release the clutch. The moment before wheel spin occurs, depress the clutch. Your vehicle will roll backwards off the obstacle. As the rear wheels hit the obstacle behind you, the vehicle will bounce forward. Make use of this forward momentum and release the clutch again. Each time the vehicle is rocked back and forwards in this way speed and momentum will increase. At the moment when you feel that enough speed has been built up, release the clutch and accelerate gently. Rocking works particularly well on rocky terrain and often in mud, and will also work in reverse. If attempted in sand however, it usually digs the vehicle in deeper.
Sand driving encompasses dunes, tracks and the beach.
These rules can be applied when driving in sand:
• Shadows in the morning and evening make driving easier.
• Engage 4WD well before you need it and lock up your transmission.
• Deflate your tyres according to recommendations.
• During the heat of the day, especially after long periods without rain, the air gaps between the sand particles will be larger and the sand will have less flotation. During the cooler hours, the sand will be more dense and will support more weight. After rain and in the early morning, moisture will compact the sand and make the going easier.
• Select the appropriate gear before tackling the difficult parts. You will need the highest possible gear that will give you enough torque to get through – try high-range first or if the sand is very thick, low-range third. A gear change in thick sand will halt your vehicle as quickly as if you had applied brakes. The lower the gear, the more chance of wheel spin. The higher the gear the greater the chance of having to change gear which could mean the loss of momentum.
• Follow other vehicle tracks. This reduces the scars on the landscape which in some desert areas remain visible for decades.
• If you need to stop, find a firmer patch and do not touch the brakes – simply slow down and let the vehicle come to a halt. Applying brakes will cause a weight shift and a little wall of sand to build up in front of the front wheels – this will make starting off difficult.
• Before starting off, or if you find starting off difficult, reverse a short distance (one metre is often enough) along your own tracks and pull away. This allows momentum to be gained before you reach the wall of sand that was created when your vehicle stopped.
• If you get stuck, try reversing along the same tracks you approached on. The opposite twisting action of the axles in reverse will help give traction. Attempting to leave the tracks may get you stuck. On your second attempt, go through with a little more speed.
Driving on sand dunes is a particularly delicate conservation issue and should never be undertaken in a thoughtless manner. When driving up and over a dune, check over the top for people, other vehicles and the sharpness of the descent on the other side.
Momentum is the single most important aspect when dune driving and everything a driver does must be geared to maintaining it, no matter how the conditions may vary. When a vehicle is on hard ground between dunes the correct speed and gear ratio for the climb must be established. In most dune conditions I recommend low range third and fourth. While second and third high range is also fine, selecting low range is advisable because if a rapid change-down to second or even first is needed is can be done in a hurry – no need to stop, and change from high to low range.
Correct gear selection in dune driving is crucial. Start off in low second and progress to third and fourth. Avoid changing gear mid-slope as in most cases it will degrade the vehicle’s momentum enough to stop it completely. However, all rules have their exceptions.
In 1996 a group of friends in a Hilux and my family in a Land Cruiser went exploring the Namibrand Nature Reserve in Namibia, where we found some exhilarating dune driving. On one particularly long steep climb the Hilux in front balked at the steep dune and came to a halt. After about eight attempts the driver had run out of options and the dune remained unconquered. Approximately two thirds of the way up there was a length of corrugations where the track became a little steeper. The corrugations were created by drivers hitting the accelerator at the base of the gradient increase. Acceleration here simply meant spinning wheels, loss of momentum and the resultant corrugations. I then asked if I could give it a go. On the early part of the slope I realised that flat out in second gear high-range was not going to give me enough momentum to overcome the difficult patch and hitting the slope with extra speed was not an option. So, when I reached the corrugations, at the moment when my wheels would start to spin, I changed into first gear and powered my way up the final 30 meters to the top. My friend, now in the Land Cruiser, with much more power and momentum at his disposal, did the entire climb in second gear. In situations like this a gear change may be required and vehicles with more power require less effort to drive. The critical driving technique was not just the gear change, but timing it over the corrugations where the wheels would lose traction anyway.
Rules of dune driving:
• Deflate tyres before dune driving.
• Keep power constant on the slope.
• Maintain the momentum of your vehicle.
• You must aim to stop at the crest in order to inspect the descent and to engage the correct gear for the descent. The aim is to get your vehicle to stop at the top, even if it means touching the sand under its belly. Ideally its nose should be over the edge and the vehicle lying horizontal pointing slightly downhill.
• You will need to decelerate as you near the top and judge it perfectly to get it right. If you stop and are still pointing uphill you will have to reverse back down and try again. Do this once you have checked the gradient and know what you are up against. Once your vehicle is successfully perched at the top, the next step is to dig away the crest that is touching the chassis between the wheels.
• Survey the drop and engage the low-range first if it’s not too steep and low-range second if it’s hair-raising. The higher gear will mean a faster drop but will prevent the sand under the vehicle falling faster than the vehicle. If this happens the vehicle will slide sideways, and that is a very bad idea.
• If it does start to slide accelerate firmly. Don’t let the slide continue! Slides on dunes turn into a roll-over in an instant. Too much speed going down a dune slope is safer than going too slowly.
Side slopes on dunes
Never attempt to go sideways when ascending or descending a dune, because if you do the lower wheels will dig in and your vehicle will roll. Loaded roof racks are ill-advised when dune driving, and a conscious effort should be made to keep the vehicle’s centre of gravity as low as possible when loading your vehicle. If the track ahead runs for a short distance along the side of a dune where the vehicle may slide, power is the only thing that will prevent the rear wheels from breaking away and the vehicle stopping at a precarious angle. Keep the power on and keep moving. If the back breaks away turn into the slope (downhill) and keep the power on. Getting stuck on a side slope is often a dangerous situation and the first priority should be to secure the front of the vehicle to prevent it from sliding any further and increasing the angle and the risk of rolling the vehicle.
When driving on thick sand tracks engage four-wheel drive even if you do not require it. Tyre wear will be reduced and vehicle control will be easier. Fuel consumption will also be improved because, even if you don’t realise it, in two-wheel drive wheel spin will occur over the bumpy patches and speed is lost. The proof of this is the effect that a two-wheel drive has on this type of road. The spinning rear wheels cause large waves of sand to be built up and, after a time, driving on these roads is like riding a roller coaster.
When driving along deep sand tracks there is a natural tendency to fight with the steering wheel. This is due to the wheels sliding over the sand with very little feel being transmitted back to the driver as to which way the front wheels are pointing. Deep tracks can be driven without a hand being placed on the steering wheel at all. But don’t be fooled by this as I once was, and play a game of chance along the narrow sand tracks in the Kalahari – many 4x4s have come to grief as the front wheels spin out and the vehicle suddenly rolls over.
On this type of track the vehicle moves as if it were on rails and the inexperienced driver will tend to fight the steering wheel and most of the time the front wheels will not be pointing in the direction of travel – the front wheels will plough through the sand, absorbing power and consuming excess fuel. Very little steering effort is needed to guide a vehicle in these conditions. Let the vehicle steer itself while holding the wheel firmly enough to catch it if it suddenly swings, gently coaxing the vehicle in the direction you wish to go.
When driving along tracks through thick bush it is important to keep the windows rolled up to eye height. This is done to prevent branches along the edges of bush tracks from whipping into the passing vehicle and causing injury to the occupants’ eyes.
Sand tracks that have very high walls are difficult to get out of. To get out of the trough, decelerate lightly, swing the wheel over quite hard and then IMMEDIATELY SWING IT BACK to just off the dead ahead position. If the steering wheel is left in the hard over position, a slide and a roll-over could result. If it works, the vehicle’s front wheels will ride over the ridge and the rear wheels will follow. If it does not, center the steering and try again. If you find it impossible to leave the track, as can sometimes happen, stop the vehicle and try it in reverse. If you are forced to leave the track due to an oncoming vehicle, stop and turn on your headlights. Try the reverse procedure pulling off to the left hand side of the track.
On two occasions I have come across a 4WD vehicle lying in the middle of a sand track on its side. On both occasions the drivers had tried to get out of a deep track. They had swung the wheel hard over and when nothing happened turned it even more. All of a sudden the front wheels hit something solid and the vehicles left the track so sharply that they rolled over.
On The beach
Beach and sand driving have obvious similarities, but other important points should be considered when driving on the beach. Make sure you carry a can of Q-20, or a similar water repellent as well as a tyre gauge and pump with you. Drop tyre pressures before venturing onto the beach.
• An outgoing tide is the best time to drive on the beach due to the extra time to dig yourself out should you get into trouble.
• Do not underestimate the speed at which the tide comes in – you may lose your vehicle if you do!
• Drive as close as possible to the water’s edge without getting splashed and you will be driving on the firmest surface.
• Beware of shiny wet patches and keep them between you and the surf – they indicate deep patches of sand saturated with water. Areas of pebbles or shells which even under the best lighting conditions are difficult to detect, are treacherous. They are invisible when the sun is low in the sky.
• Avoid driving on an unfamiliar beach at night.
• Give way to anyone who appears to be having difficulty, and watch out for children.
• Too low gear ratios will induce wheel spin unless the driver is very careful about how he applies his right foot.
• Use low range. A quick change down is then at hand. Be alert, beach driving can be extremely hazardous to your insurance premiums.
• In South Africa, a blanket beach ban has been imposed and vehicles found unlawfully on a beach can be confiscated.
Off-road vehicles are often required to forge through deep water. Before doing so, check the vehicle manufacturer’s specification data sheet on maximum wading depth, (or the vehicle handbook).
Water is ingested by the engine if the engine stalls and water is sucked up the exhaust pipe or if the water is too deep, the engine intake can suck water into the combustion chambers. SHOULD THIS HAPPEN DO NOT ATTEMPT TO RESTART THE ENGINE. IN MANY CASES IT IS THE RESTART THAT CAUSES THE SEVERE DAMAGE.
In deep water the engine cooling fan splashes water around the engine bay, so either keep engine revs low, or remove the fan belt. Viscous-coupled cooling fans are ideal because when they hit water the friction slows the fan, reducing the splash. Some vehicles come equipped with bell housing drain holes which allow oil collecting in the bell housing to drain away. These holes must be sealed to prevent water coming into contact with the clutch.
Many years ago (when I was a lot less careful about such things) my vehicle was called upon to extract a yacht from deep water. I was unable to seal the bell housing because of a missing plug but I went ahead regardless and paid a high price. Water entered the bell housing and because the water was very cold, and the engine and gearbox were quite warm, the cooling effect caused water to be sucked into the engine through a leaking rear main bearing oil seal. The water, which was already mixed with fine sand, mixed with the engine oil and wrecked the main bearings. The engine had to be completely rebuilt.
Slow speed is essential and low-range second gear is recommended for most wading conditions. When entering the water do so slowly and avoid creating a splash that will wet electrical components. Drive at a speed that creates a clean bow wave. If you have ever seen a boat moving at speed and then slowing down, you will have noticed the bow wave catching up and pushing the boat from behind. This is exactly what happens to a vehicle in deep water. If you have created a bow wave and lose traction, the bow wave will push your vehicle forward as it catches up. This little push may be just what is needed to get you through a sticky patch, or up a river bank.
When crossing running water, test the depth and strength of flow before proceeding. If the flow is too powerful to walk against, rest assured that driving through it will be dangerous. Moving water will create more turbulence than still water, so consider this when calculating the depth. Move diagonally across the flow with the water pushing you. Crossing still water is safer but the possibility of deep sediment is more likely.
After wading, bell housing sealing plugs should be removed. Inspect the engine air filters if you think water may have entered the carburetors. Water can contaminate gearbox and axle oils by entering through the breather valves. Because oil floats, it is easy to remove this water. Allow the vehicle to stand for a while and remove the drain plugs. The water will drain first and when you see oil, stop the draining process. If your engine oil has turned a milky grey colour, water has entered the oil pump. You will need to drain away the oil, flush the engine at least twice with oil or engine flush and then refill with new oil. Universal joints must be pumped with grease after being submerged.
Should a petrol engine ingest water into the cylinders it normally stalls before any serious damage is caused. This however is not the case with diesel engines – they are often destroyed if this happens.
When a series of ruts and troughs follow each other it’s often referred to as an axle twister. Driving axle twisters without a rear diff lock requires a technique I call push-and-pull. During a trip to the Linyanti in 1990, I was confronted by a broad mud flat where the elephants had walked. When they had been there it was wet and their huge footprints made hollows as deep as my knee. All across the flats were thousands of these footprints, now made as hard as rock, baked that way by the October sun. A speed over three kph would have left my Land Rover in ruins so the push and pull technique was used.
The push and pull technique:
• Engage four-wheel drive/lock the centre diff, low range 1st or 2nd.
• Assuming the right wheel enters first, let it drop into the hole. As it bounces upwards apply the accelerator gently.
• The left rear will fall into a hole. As this happens the front right wheel may leave the ground. At this time the rear wheels are pushing.
• As the front right wheel falls, (this is critical), ease the accelerator. The front wheel, as it strikes the ground must not spin. It will, if it is not spinning, grip. Now the front wheels will pull.
• As the front wheels pull, apply gentle accelerator.
• The rear wheels will move through the holes, probably one will leave the ground. As it does so, the left front wheel may lift and then fall.
• The process of easing the accelerator as the wheel falls begins again.
• Using the push and pull technique with too much speed will make it too difficult to apply as well as bouncing wheels and traction loss.
Driving along V-shaped gullies must be done with extreme caution. If one side of the vehicle slides down, and the wheels drop into the gully, there is a very good chance that the vehicle will get stuck. Getting out is also very difficult and digging may not work. One has to lift the lower wheels out of the gully, and to do this without momentum is tricky. In this situation, axle differential locks help a great deal.
When a V-shaped gully is entered, it should be done at an angle so as not to drop more than one wheel into the trough at a time. Exiting a gully should also be done at an angle so as not to allow both wheels on the same side of the vehicle to drop into the trough. Good axle articulation will assist a vehicle negotiating this type of terrain.
Deep parallel ruts should be negotiated with one wheel in and one wheel out. If you allow both sides to drop into the rut the chassis may bottom out and progress could be halted. This would mean a great deal of digging to clear the underside of the vehicle to put the vehicle’s weight back onto its wheels again.
When crossing a ridge, stay at right angles to the ridge, passing both wheels on each axle over the obstacle at the same time. Crossing at an angle could result in lifting a wheel off the ground and the loss of traction on that axle.
When negotiating a trough, cross at an angle so as to drop only one wheel at a time into the trough. This will always keep at least one wheel from either axle on firm ground. When moving along a series of troughs do so carefully and slowly, otherwise the differential may be grounded if a wheel drops to one side.
Driving over salt pans is a nerve-racking experience and to do it successfully will require experience and luck. Don’t be fooled by the apparent firmness and dryness of the surface. Underneath lies thick, black, enveloping mud.
Before you venture across the pan, skirt around the edge to find the shortest possible route across. If you have decided to go across test the surface by walking some distance in front of your vehicle. If your feet are breaking through the crust, then do not attempt to drive across, no matter how broad your tyres are. If your feet are stepping on firm ground, then dig a hole about 25cms deep. If the earth is hard and dry, then it may be safe to cross. Unfortunately, there may be areas in front of you that are still soft.
The lower your tyre pressures are, the better your chances of getting through. Engage four-wheel drive, lock differentials and hubs, select low-range third or fourth and proceed fairly slowly. If you rush and the surface breaks you will be a long way from the firmer ground behind you. Follow the direction of other vehicle tracks if they look fresh, and drive parallel to them while making your own tracks. By taking it slowly you can assess the firmness of the surface by how much power you are giving to the wheels. Look down at the wheels to gauge the depth of the tracks you are making.
If the surface breaks and you start sinking, either floor the accelerator or stop. Accelerating may get you through the soft patch, but if not you will be a long way from firm ground when you bog down.
By stopping immediately you feel the vehicle sink it will be easier to dig out because of the close proximity of firm ground and suitable anchor points, such as another vehicle. Avoid sudden movements of the steering wheel. Turning will only make matters worse, because your wheels will act as a plough. If you choose to stop, attempt to reverse in your own tracks or try to steer out by making a gentle turn. If your vehicle resists leaving your tracks, straighten the steering wheel and let the vehicle steer itself. If you are making progress and the reverse is getting you out of trouble, all is well. If not, the mud may be so bad that even digging is sometimes pointless. If you have another vehicle with you, which is highly recommended when driving on salt pans, do not waste any time – start the recovery operation without delay. Work fast – your vehicle may be sinking. Watch the recovery vehicle closely – and don’t get that stuck too!
Bogging down on a salt pan is a miserable experience. The mud is the worst kind you are likely to find anywhere, and without the aid of another vehicle equipped with a winch it may be days before you get out. Above all, don’t take driving over salt pans lightly – they are treacherous. In Botswana vehicles are consumed by the pans almost every year. Do not stop and look at the scenery, no matter how solid the surface appears. Lastly, please consider both the environmental effect your vehicle tracks will have on the pans, and your fellow travellers that will pass after you have departed – in any event, it is far more pleasant and a great deal safer to walk than to drive.
Rough bush tracks
Although four-wheel drive may not be needed for traction, it is wise to engage it. This will reduce wear on transmission components and will afford the driver greater control. Avoid the constant use of brake and clutch and rather select a low-ratio gear that will keep the vehicle going at a steady speed. Look well ahead at the track surface and beware of sharp rocks that can tear tyre sidewalls. Thorns and narrow bush tracks. Keep windows wound up at least to eye-height when travelling along narrow bush tracks. The dangers of eyes and faces being spiked by thorns is then kept to a minimum.
Boulders and river beds
Engage 4WD and lock the differentials, even though you may think you do not need it. Select low-range first gear. In this gear, wide throttle openings should be avoided. Beware of the vulnerable parts of your vehicle such as the axle differentials and gearbox casings, especially if they protrude below the chassis frame as in the case of many 4×4 pick-ups. To avoid striking these, make sure that the wheels ride over the higher boulders, clearing the axle and chassis.
Use the rocks around you to reduce departure angles, assist a wheel to climb a step or prevent the vehicle running out of clearance.
Thumbs folded inside the steering wheel rim can get hurt when driving over rocks if the front wheels hit a rock hard and the steering kicks. Keep them on the outside.
Fit a grille guard to prevent grass seeds from clogging the radiator and causing overheating. Fire may be caused by dry grass wrapping itself around the prop-shaft or exhaust. The grass dries out and ignites, so frequent checks must be made and any grass collecting under the vehicle must be removed immediately. Tall grass also hides ditches, logs, ant hills and rocks, so caution is vital. Remember that your tracks will be clearly visible for some time after driving over grass, so in the interest of conservation use existing tracks if you can.
Long stretches of unsurfaced roads present their own dangers. Firstly engage four-wheel drive and lock the centre diff if you have one. DO NOT lock the rear axle diff. If you wish to overtake, check that your outside wheels do not hit the sand that piles up at the edge of the road; it will drag at the wheels on that side of the vehicle and can cause a spin. Secondly, if the road is convex, overtaking or even avoiding oncoming traffic can put your vehicle at a tilt, and this can cause a dangerous slide. If you see an oncoming truck throwing up clouds of dust, take the precaution of either slowing down to a crawl and getting well clear, or alternatively leaving the road and stopping altogether. There are very good reasons for this; for one thing, you will avoid loose stones being thrown up like bullets. For another, there could be another oncoming vehicle overtaking the truck through the dust. I was given this advice by an experienced traveler on the Caprivi road from Kongola to Katima Mulilo when in days past the truck drivers would race each other side-by-side. Only one of the trucks could be seen by oncoming traffic.
Some desert roads are made from a substance called calcrete that appears blinding white in the midday sun, and can be very dangerous. They are particularly prone to the effects of big trucks and storm water, and after a week of rain can be transformed from a smooth dusty flat that can be covered at 90 kph, to a virtually impassable quagmire.
A driver needs to be very alert when driving on calcrete and driver changes should be regular. Driver concentration can be hard to maintain on long stretches and surface changes are very difficult to see against the blinding white.
If you see a deep rut or trough in front of you and it’s too late to stop, apply brakes as hard as you can without locking the wheels. Do this until the very last moment and then, the instant before the front wheels hit, release the brakes. As the foot brakes are released, the vehicle’s centre of gravity moves towards the rear and weight is taken off the front wheels. Now the vehicle hits the trough with less than the normal weight on the front axle. Doing this could mean the difference between a broken axle and simply a heavy bump. Swerving and hitting the trough sideways could roll the vehicle.
One more piece of advice: if you are travelling on a busy and dusty road, turn your headlights on and stay visible through the dust.
Corrugations are to be found on all dirt roads that are used by heavy vehicles and are especially bad after rain. They can cause a great deal of damage if driven over too fast. Suspension components are stressed to extreme limits if the vehicle is heavily laden and torsion stresses on the chassis frame can cause cracks in the steel. Corrugations can also cause loss of control, especially with vehicles that are softly sprung. Upon hitting the corrugations, vehicles like these tend to go into a slide, losing traction at the back end. This tendency is dramatically reduced when in four-wheel drive.
Loading a vehicle does tend to dull this tendency, but an overload will have the opposite effect, in which case over-steer increases dramatically. Early Land Rover Discovery and old Range Rover are particularly prone to this. By fitting gas shock-absorbers this tendency is reduced.
Driving at night
If you intend traveling through Third World countries at night, my advice is avoid it at all costs. The dangers cannot be over stressed. Third World countries are generally unfenced, so cattle, goats, chickens and antelope are a constant danger. If you collide with a cow at 80 kph you will be in a lot of trouble! You may wreck your vehicle and if you are lucky enough to get out unhurt, the local tribesman will require compensation. Litigation against owners of animals straying onto public roads in Third World Africa is expensive and time consuming, and in most cases unsuccessful. Trucks without lights are an even bigger danger. They are normally filthy and any reflectors fitted will have a thick layer of dust on them so that when you do see them it may be too late to avoid a collision. What is more, on dirt roads at night if there is a lot of dust, your visibility will be impaired by the light bouncing back off the dust, making your long range lights useless. I cannot stress this point strongly enough: it is extremely unwise to travel at night in the Third World.
Snow and ice
Snow chains are particularly valuable and if only a single set is available, place them on the rear wheels for tricky uphill climbs and on the front wheels when descending steep slopes. When tyre chains are fitted to only the front wheels there is the tendency for the back wheels to slide out, so extreme care should be taken.
Operating a 4×4 in snow and sub-zero conditions:
• When a vehicle is parked for long periods, lift the windscreen wipers or they will stick to the windscreen otherwise.
• Do not leave the hand-brake on overnight, as some hand-brakes freeze. Rather park on level ground and engage low range first gear.
• Weather conditions in high altitudes in winter can change very rapidly and it is imperative that when exploring such areas in winter, food and water rations for at least three days should be carried.
I have experienced four blow-outs while driving at speed in a loaded 4×4. Three occurred on the rear wheels and one on a front. 4x4s tend to have large wheels and tyres and so have a high center of gravity exacerbated if the vehicle is carrying a loaded roof rack. Catastrophic tyre and tube failures (blowouts) cause a vehicle to become difficult to control even if the failure occurs on a rear wheel. In such a situation the natural reaction is to stop as quickly as possible, but this is not always the most appropriate course of action. Hitting the brakes with any force in a blow-out situation tends to lead to loss of steering control followed by a slide. If the wheels strike a ridge or trough, even a shallow one, the vehicle can easily roll over. Avoid hitting the brakes. Simply take your feet off the pedals and gently change down one gear ratio. Take your time. Keep the vehicle on the road and away from the camber that will accelerate a slide. Causes of blow-outs range from under-inflation, overloading or a twisted inner-tube. Engaging four-wheel drive or locking the centre diff on gravel roads will reduce the chances of control loss caused by blowouts by 80%.