Before reading this section I would recommend you read and fully understand the previous section “four wheel drive how it works” as this explains the operation of a basic four wheel drive system, this needs to be understood to benefit from this section.
This section is devoted to teaching beginners the basics of off road driving, these are in no way definitive, but do require the driver to have a feel for the vehicle, many of the techniques do require practising to get them right. This will lead to experience, something which can only be gained and not taught, and something which is a life skill which can also be applied to normal road driving under adverse conditions. Younger drivers will have to adopt differing driving styles as off road driving requires the use of the gearbox to hold or slow the vehicle by changing down through the gears, many will have been taught to use only the brakes to stop a vehicle in their driving tests. Those of us who are more experienced (old or aged) were taught to change down through the gearbox and then use the brakes as well.
We need to begin with one old saying, “when off road driving you must travel as slowly as possible, but as fast as is needed” a poignant saying when it is understood so learn this saying and remember it. This saying applies to momentum, so what is momentum? In technical terms it is mass multiplied by velocity; in understandable terms it is the speed multiplied by the weight of the vehicle for any given condition. Understanding momentum is necessary for off road driving as it is something which is very useful to use, but can be lethal if it is not controlled, to explain momentum and how it affects vehicles we can do a simple test.
Drive your vehicle along a straight empty road at 20 MPH then depress the clutch and release the throttle, the vehicle continues to travel for a distance before finally coming to a halt, repeat this at 30 MPH and then 40 MPH and examine the distances travelled at each speed. This is momentum which is carrying the vehicle along as it freewheels, so now we know momentum and understand how it works, now we know this we can begin to understand how it can be a useful off road driving tool, and how it may bite us if we do not understand it.
We need to know the basic vehicle off roading technical information, this is approach and departure angles, ramp breakover angle, ground clearance and wading depth.
Approach angle is the angle from the front wheel to the bottom of the front bumper, this is the maximum angle the vehicle can approach and safely climb without ripping off the front bumper, or catching and damaging it.
Departure angle is the angle from the back of the rear wheel to the bottom of the rear bumper, and is the maximum angle of slope the vehicle can travel down onto level ground without damaging the rear bumper.
It is necessary to understand these angles as they may not necessarily be from a slope to level ground, it may be that you travel down one hill to a gulley, only to immediately begin climbing another hill. Judging these will be gained through experience and practise, another consideration is that vehicles angles are measured on level ground; if the front suspension is compressed such as travelling down a steep slope it will reduce these angles.
Ramp breakover angles are measured from two points to the centre of the underside of the vehicle, these two points are the rear of the front wheel and the front of the rear wheel. Ramp breakover angles are the maximum angle which a vehicle can travel over an edge from flat or other ground to a downhill slope without bottoming the vehicle out and leaving the front wheels trailing in mid air with it supported on the rear wheels and the chassis.
Ground clearance is the height underneath a vehicle, it is necessary to know this as it allows us to judge whether the vehicle will pass safely over an object such as a boulder, or whether we will need to get out of the vehicle to remove it; or take another line around it. Ground clearance is usually measured at the lowest point of a vehicle; but not always, as some points under a vehicle are lower than others, get under the vehicle and see where the low points are, these will be the suspension arms or the differential pumpkins in the centre of the axles.
Wading depth is the maximum depth of water a vehicle may safely cross, if this is too deep the vehicle will suck water into the air filter, then into the engine; this is known as a “hydrauliced” engine as water does not compress, it simply trashes the engine. Avoiding the expense of an engine is a must as it is such an expensive repair.
Side slopes have been deliberately omitted, this is the sideways angle a vehicle can lean, for a beginner I would not advise travelling across a side slope as anything such as a small hole or rock could cause a vehicle to topple sideways.
Younger drivers will have adopt a different driving style to that they were taught, older drivers may omit this section.
When driving on the road it is best to use the vehicles gearbox to slow it down, it is simple as lifting off the throttle fully, and allowing the vehicle to slow to about 1200 RPM for diesels and 1500 RPM for petrol’s, then change down to the next gear. Repeat this until you come right from top gear through to second gear, and do not apply the brakes as it is not necessary; it is necessary to make better judgements as you will have to be more observant in watching traffic and react much earlier than simply applying the brakes. This serves two purposes, it saves the brakes and makes sure you understand how a gearbox can work, and develop a fell in slowing a vehicle down when it is used in conjunction with the brakes.
If you simply apply the brakes the vehicle is doing just that, it is reliant purely upon the vehicles brakes, but if you use the gearbox and the engines brakes you multiply the stopping power of the vehicle by using engine power and brakes. Petrol engines use vacuum servo’s, diesels use brake booster or vacuum pumps to reduce the force at the brake pedal; changing down a gear increases engine revs and the boosting power of the servo or vacuum pump, as well as increasing engine power and torque. This now increases vacuum, the engines power and torque, and the power of the brakes; which are all combining to slow or stop a vehicle, it also saves brake wear and gives experience of using the gearbox which is beneficial to off road driving.
Drive your vehicle across a variety of easy terrains, these may be gentle off road routes in conjunction with another vehicle which may recover you if you become stuck; which you will at some point. This will give an indication of the feel of the vehicle in four wheel drive, I would advocate using a grassy surface, shallow mud, shallow water (less than 6” – 150mm) and across gentle rocky surfaces so you can feel how much grip the vehicle has. You will note the drag in many of the conditions, and how much additional engine power and torque you will need to cross them; you will also feel the power band of the vehicle and note what engine revolutions you will need to make steady and consistent progress. You will also note that momentum of a vehicle as you travel up or down gentle slopes, and where you encounter engine braking through selecting different gears.
Practise in this terrain until you are confident in the vehicles abilities, try using different gears to traverse terrain, and try different approaches and different speeds at the differing obstacles.
Ruts
Driving in ruts seems one of the easiest things to do, but this is where many beginners come unstuck as they do not watch the terrain, or fully appreciate the vehicles underbody clearance. Where possible the best rule of thumb is not to drive in ruts, but often this is the only way you can traverse a particular route, if the ruts are excessively deep due to agricultural or forestry vehicles using the route you will encounter a condition called “high centred”. This is when you have insufficient underbody clearance, and are travelling too fast, your reaction times and momentum ensure a vehicle continues to travel before coming to a halt, it will be sitting on its chassis or underbody protection with its wheels in the air. The old adage of as slow as possible and as fast as is needed” suddenly springs into your head as you fully appreciate the beauty of being high centred; and yes we have all been there and done it, even though we may not admit it.
Ruts on reasonably solid ground may not present too many problems, but when they are in mud or sand we encounter another problem, we try to steer out of them and the vehicle follows them, and we cannot get out of them. There is a technique to get out which requires practise: we reverse up and travel forwards at a higher speed, we suddenly and sharply turn the steering wheel and accelerate hard at the same time, and this generally gets us out. This technique works through the action of the steering, the power at the front wheels, and the action of the open differentials which suddenly change through sharply turning the steering wheel and increasing power.
Where you may encounter problems with ruts, it is prudent to get out and walk the route; you can get out the shovel and clear the central hump and throw this dirt into the bottom of the ruts to decrease the hump and reduce the depth of the ruts.
Certain types of ruts can create another condition known as “cross axled”, this is where a rut or gulley is crossed at the wrong angle, this leaves one wheel on one axle in the air and its diagonally opposite wheel on the other axle in the air. Power takes the line of least resistance, this means equal power is being transmitted to both axles, but the flailing wheel on each axle simply spins and the vehicle is going nowhere. Preventing cross axling is as simple as changing a crossing axle to ensure you have both wheels on one axle in solid contact with the ground, and enough forward momentum to push you across the gulley to put both wheels on the other axle firmly on the ground. It does not matter which axle has both its wheels in contact with the ground as long as one of the axles wheels are firmly planted with grip.
Mud
Mud is one of the most awkward conditions to master as it varies considerably, it may range from spongy bog type mud to wet slurry to cloying thick clay, it is these varying conditions which need to me mastered and experience gained in identification. Mud is the one condition which causes the most mechanical damage to a vehicle from hidden objects such as buried boulders or tree branches which may have fallen from an overhanging tree. Mud depth can vary considerably and hide other objects such as buried ruts, beds of streams, and can suddenly become very deep without warning, mud density can vary as in hot weather the surface can seem firm, but underneath it is still wet. Driving a vehicle across this seemingly firm crust will cause it to break through, it may support you standing on it, but it will not support a couple of tons of Japanese off road steel.
Always get out of the vehicle and walk the mud, prod it with a stick to check its depth and to find any hidden obstructions such as buried rocks and ruts then proceed with your vehicles, and only one at a time. Mud drags a vehicle down and saps engine power through this additional drag, once it has been checked we need to gain momentum to carry us through, select four wheel drive, low range, and third gear. This allows us to gain enough forward momentum while entering the mud and to maintain this momentum as we travel through the mud, it needs a consistent and steady throttle so do not accelerate if the vehicle begins to slide. If a vehicle begins to slide we simply ease off the throttle enough to stop the wheels spinning, but not too much so that we lose forward momentum and engine power which would bring the vehicle to a stop. One useful trick when a vehicle begins to slide is to quickly rock the steering wheel from side to side slightly and continuously, this makes the differentials work in our favour, and allows spinning wheels the opportunity to clear their treads through the spinning motion. This technique may not work every time, but only having one vehicle crossing mud at a time means other vehicles are on firm ground to recover you; you may need more forward momentum to carry you through, so a higher approach speed, or a different line. Once you are pulled out of the mud you can try again.
If you become stuck in mud there is the “rocking technique”, it requires practise but is very useful to learn as it can extract a stuck vehicle in most circumstances.
If you become stuck going forwards you engage reverse and drive backwards as far as possible, as soon as the wheels slip you dip the clutch and allow the vehicle to move forwards on its own, then let out the clutch and repeat. Each time you will travel a little further and increase the length of the gulley’s you have created, you may need to move to first gear as they become longer; once they are long enough you can accelerate with enough force to get yourself out.
Remember the basic rules: steady and consistent throttle, do not accelerate with spinning wheels as you will dig in, never use your brakes, and always check the route by walking it first and prod it with a stick for obstructions and depth.
Rocky Terrain
Rocky terrain is usually visible unlike muddy terrain, and you can see where you intend to pick a route through, but rocks are a loose number of objects which are easily dislodged by the power or weight of a 4X4. Moving rocks are the main problem as they can become dislodged and thrown up under the vehicle or tip sideways in soft ground underneath them, leaving them sticking up higher than the vehicles underbody clearance, thus causing damage. Loose rocks can be thrown out from behind a vehicle which will damage following vehicles, so always travel through one vehicle at a time. Many rocks of certain types such as slate, spar, granite, and many others have razor sharp edges which can slash through tyres, so always walk a route with rocky terrain before driving it.
Wet rocks can become as slippery as ice, you may have travelled a route many times in the dry, without problems; but a light misting of drizzle makes them treacherous and very slippery, it is this which can cause a vehicle to slip forwards, backwards, or sideways; or you may get in somewhere but cannot get out.
When crossing rocky terrain there are several things we can do to ease our passage and secure the rocks to minimise damage, the most obvious is to remove any awkward or problematic rocks as you walk. Where there are large gaps in rocky surfaces, or steep steps we can do a little road building by filling them with progressively smaller rocks, this is then topped off by shovelling a little sand or fine dirt in between them to anchor them more securely.
When driving across rocky terrain we need total control and minimal speed, we always select four wheel drive, low range, first gear; this gives us total control and time to react to any problems, and never use the vehicles brakes unless it is to stop.
Remember the basic rules: Check the terrain for obstacles, use and maintain the minimum momentum, do some road building, and always low range first gear.
Sand
Sand is somewhat unique as it comes in many types which cause numerous problems for novice drivers, but is one of the easiest terrains to master as it is usually very consistent once we know its characteristics. Sand tends to be at its best to be driven across when it is damp as it is reasonably firm, wet sand is soft and vehicles sink into it, and dry sand is soft and almost impossible to gain traction on, so never drive on sand alone. If a vehicle is stopped on wet or dry sand it will sink, it is as simple as that, and it will continue to sink up to the floor if it is not recovered by a specialised recovery vehicle, so always take care when driving on beaches where allowed as the tides soon engulf a stuck vehicle.
Sand is the most power sapping terrain so often it is low range, and the highest gear you have in your gearbox, 4th for four speed boxes, 5th for five speed boxes; you need to build the most momentum and the highest speeds when travelling across sand. Keep your engine speed up and well into the power band so it overcomes this huge drag, and if it falls too low be prepared for a fast downshift to the next gear, but avoid this if at all possible. Never spin your wheels as you will dig in far quicker than anything other than slurry type mud, and always carry a shovel and never travel across sand alone, the other vehicle can always summon help if you become stuck.
Recovery on sandy surfaces is quite easy, if you become stuck you simply shovel the built up sand from around the wheels and dig two long tapered trenches in front, or behind the vehicle and drive along them, building up speed until you are free. If the vehicle is high centred you will have to scrape all the sand from under the vehicle until it is firmly in contact with the ground. Sandy surfaces are not confined to beaches; many areas have sandy soil which may offer the same problems and solutions.
One other method of recovery is the vehicle rocking method, this works well on sandy surfaces if the vehicle is not sinking or high centred.
Remember the basic rules: Check the terrain for condition, use and maintain the maximum momentum and speed use four wheel drive, low range, and the highest gear.
Water
Crossing water is one of the most difficult things to do in a 4X4, but can be made so much easier if the basics are understood AND FOLLOWED TO THE LETTER irrespective of what your off road driving experience is. Many experienced drivers often ignore the basics and get themselves into trouble due to the power of water, and the power it can exert on a vehicle. Many problems conspire against us with water crossings, and what would normally be a simple crossing can end up being fatal, look at the American reality shows which show actual rescues of the numerous vehicles washed away while making a simple water crossing.
Water is a problem for many reasons, the bottom is often soft like mud, and it often contains many unforeseen obstacles such as rocks, and it has the ability to drown an engine, or draw water into the engine to hydraulic it.
Before attempting to cross water you need to make a careful assessment, how deep is the water? It is often difficult to assess this by looking at it so always use a measuring stick to check its depth all the way across.
Does it contain obstacles such as rocks or boulders which exceed our underbody ground clearance? And does it have any depressions into which a wheel could fall to exceed the vehicles wading depth, causing the engine to suck in water and hydraulic.
Is the water shallow enough to pass under the vehicles sills? If not the rising water up the side of the vehicle will contain enough force to push our vehicle sideways, and once up the side of the vehicle it always rises higher.
Is the bottom of the water solid enough to support our vehicle? It may support the weight of an average adult but not a couple of tons of steel.
Is our vehicle in good condition to allow it to wade successfully? Are the axle breather pipes up high enough and is the air intake up high enough, are the door seals intact, well you soon find the answer to that in water.
Are the approaches to the water reasonably shallow to allow a good approach angle into the water without immersing the engines air intake, and are they good enough to let the vehicle exit safely.
Now we see some of the factors which affect water crossings we can now see how any number of them can conspire against us to create problems. When we drive across water crossings we have to adopt a few simple rules, engage low range second gear to give us control and traction, keep the engine revs high enough to maintain pressure in the exhaust, but not too high that the fan sprays water all around the engine compartment, particularly with petrol engines. Enter at a shallow angle and ensure the water passes under the vehicles sills especially if it is running water, and gently accelerate once in the water to form a bow wave in front of the vehicle as it pushes through the water. Bow waves form several inches in front of a moving vehicle as it moves through the water, immediately in front of the vehicle the bow wave is lower, and as it passes down the side of the vehicle it becomes lower still, watch a boat pushing through the water at low speeds, its exactly the same. Keep moving on a consistent throttle setting, or use the hand throttle; and never stop in the water or turn off your engine as water could flood the engine through the exhaust pipe. Make a smooth exit from the water and allow your vehicle to stand to drain out any water gathered, with its engine idling. Never approach and enter the water at high speeds, the resulting splashes may make good pictures or TV footage, but an engine or other damaged items simply make you look a fool, especially if you drown the engine in a petrol model.
Remember the basic rules: Check the water for all condition, use four wheel drive, low range, second gear, steady and consistent throttle, do not stop in the water, stall or turn off the engine, and approach at a shallow angle.
Hills
Hills are the most encountered condition in off road driving, for most novices the urge to climb them exceeds their experience and capabilities, this leads to serious accidents from inexperience and over confidence, remember, on hills vehicles roll and do not stop easily. Hills should always be ascended or descended in a straight line, and never across them as momentum and uneven ground conditions could easily topple them and cause untold damage to vehicles and occupants.
Hills can be broken down into climbing and descending, these will be treated as two separate issues.
Hill climbing encounters many of the previously mentioned conditions so we need to act to overcome these conditions to climb hills safely, and know how and which gears to select to prevent sliding vehicles and wheelspin. Before a hill climb is undertaken we should always walk it to check what is on the other side and to check the bottom approach angles and ramp breakover angles at the top, many accidents have occurred because of these basic failures, particularly in unknown terrain. Once we have ascertained these we can now begin our hill climb. Select four wheel drive, low range, and either second or third gear, correct gear selection depends upon the steepness and length of the hill as well as the engine being a petrol or diesel. Move towards the hill with some speed to build up momentum before climbing and climb with a steady and consistent throttle to prevent the vehicle slipping sideways or wheel spinning, keep this steady power on and the engine revs fairly high. For diesel engines it is recommended that 3000 RPM, or petrol engines 4000 RPM are an ideal engine speed to approach the hill as this is well above the vehicles maximum torque band, as the engine revs die they will drop into the ideal torque band. If wheelspin or slip is encountered there is too much power so simply lift off the throttle slightly to maintain forward motion, and allow the wheels to bite again, and then apply power gently to continue the climb. As you crest the top you simply decrease the throttle input slightly to slow the vehicle as it exits the climb.
If it all goes wrong, what do we do? Simply stop the vehicle by depressing the clutch and footbrake together to stop the vehicle, hold it on the footbrake, and never the handbrake; and select reverse. Ensure the steering is straight and lift off the clutch to its biting point, when this is reached simply release the footbrake and clutch together and the low gearing and engine power will allow a fully controlled descent to the bottom of the hill.
What happens if I stall the engine because I have selected too high a gear? You have two options, one is follow the above procedure to hold the vehicle on the hill and restart the engine, then follow it for a controlled descent. One other option is to depress the clutch and footbrake and switch off the ignition, turn it on again and let the glow plug light extinguish, release the brake and clutch together while turning the starter key, the downhill momentum and starter key will start the engine. This will give us another variant of a controlled descent.
Vehicle descents are totally different, to descend a hill we need to make our checks to ramp breakover angles and departure angles at the bottom of the hill, select four wheel drive, low range, first gear, and let the vehicle creep forwards. Do not touch the clutch or footbrake as this well end up with the vehicle barrelling forwards uncontrollably if the clutch is pressed, if the brakes are applied it will simply skid out of control with no working steering.
What happens if the vehicle gathers momentum and slides on a steep or slippery slope? Simply accelerate gently until the wheels stop sliding, then gently decrease the throttle until it slows again, never use the brakes as it will just slide out of control.
Hill climbing is one of the most responsive of all off roading techniques to master as very controlled throttle inputs, correct gear selection, and engine revs add up to a correct and safe hill climb, you never use the brakes, only the engine power to control you.
All these techniques require mastering to become adept at exploiting your 4X4, and practise is essential, this will unleash a whole new world of driving techniques, and new found skills, begin slowly and develop them.
It may be beneficial for beginners to print off these techniques and laminate them, they can be kept in the vehicle for future reference until you become established and in harmony with driving your vehicle to become a demon off road driver.