There are a great many factors and design imperatives that go into the making of a usable and reliable 4WD vehicle; but even so, as yet there is unfortunately no such thing as a perfect 4×4, or 4WD vehicle. Or even one that is all things to most people. What is a 4×4 to one person, is likely not 4×4 to another, so which 4×4 is for you?
However, in purely technical terms, a 4×4 is merely a vehicle that has the capability to traverse terrain that most other vehicles cannot, i.e. terrain that does not consist of smooth and/or paved surfaces. How well any particular 4WD vehicle does this depends on many factors, such as the available power, wheel base, driving wheel configuration with regard to the number of driving wheels engaged at any one time, the type, tread width and pressure of the tyres, type of suspension, overall weight, speed or momentum, construction of the vehicle, angle of inclination or declination of the terrain itself, and perhaps most importantly, the skill of the driver all playing critical roles in the efficiency of a 4WD vehicle.
However, there is more to it than all that; 4WD vehicles represent many different things to many different people, with the result that manufacturers are hard-pressed to keep up with the expectations and demands of the buying public, which mainly fall into two categories, the first being buyers of luxury SUV’s with some off-road capability, and the other being buyers of “proper” 4×4 or 4WD vehicles. For our purposes, the two types of 4WD vehicles can be classed as follows:
Which 4×4 “Proper” or “Real”
Making a choice from the myriad of possible configurations is more than a little difficult; not because “proper” 4WD vehicles are bad, but because of the multitude of possible configurations; for instance, rock climbing or Saturday morning 4×4 trails demand a totally different type of vehicle than the ones you would take on an overland Cape to Cairo expedition.
With that said, which 4×4 do you buy, because there seems to be as many possible configurations available as there are places to go to. The problem does become somewhat clearer however, if you bear in mind that the main consideration should always be that the 4WD vehicle must be fit and suitable for the purpose to which is going to be put. If you are shopping for an expedition vehicle, you would be well advised to keep at least some of the following points in mind.
So, let’s look at some options in the “real” 4WD vehicle category:
• Petrol or diesel engine?
Apart from getting further with a litre of diesel than with a litre of petrol, if you are in a pinch, a diesel can run on almost anything. Alternative fuels like biodiesel made to ASTM standards, can be used with no adverse effects, and vegetable oils such as sunflower, canola, olive or even strained, used engine oils can be used in dire emergencies, albeit for short periods only.
Not that we recommend running your 4×4 on used engine oil, or straight vegetable oil for that matter, but at the risk of putting too fine a point on this, a petrol engine runs only on petrol. Additionally, diesel engines do not have electrical ignition circuits that could get wet, short out and leave you stranded.
• Which 4×4, Short or long wheel base?
Weigh the options carefully; a short wheel base may not get stuck so easily, but a long wheel base 4WD gives you more loading space. Unless of course, you plan to tow an off-road trailer with your short wheel base vehicle.
•Which 4×4 transmission, manual or automatic?
In Africa, flash floods can turn dry river beds into raging torrents in a matter of minutes. Water crossings with a manual 4×4 transmission require that you do not use the clutch to prevent clutch slippage and thus risking stalling in the middle of a raging torrent. If you plan on doing more than the occasional water crossing, an automatic transmission might be the better option.
• Full- or part time 4WD?
Both systems have advantages and disadvantages: a part time system offers significant fuel savings; however, a full time system does not improve handling, braking or general performance. All it really does is save you the hassle of manually switching between full time and part time 4WD, apart from the increased traction, of course.
• Power steering or not?
Sustained off-road driving can be extremely strenuous and you may be glad you chose the power steering option. Powerless steering can also be hazardous to your health; if your thumbs are in the wrong position on the steering wheel when you hit a rock or other obstruction with a front wheel, you could easily fracture a thumb or even a wrist when the steering wheel suddenly and violently kicks back.
• Suspension modifications or not?
This depends on what you need; manufacturers spend a lot of time and money in efforts to strike the right balance between the performance, durability and fitness of a particular component for its purpose. Under “normal” off-road conditions, suspension modifications to increase load capacity and/or ground clearance should not be necessary. In fact, even a slight increase in ground clearance could have a potentially disastrous effect on the centre of gravity of a loaded 4×4 vehicle.
On the other hand though, most 4WD vehicles would require suspension modifications when serious off-road obstacles, as those on Grade 5 4×4 trails are to be negotiated successfully?
• Independent front suspension, or not?
While independent front suspension systems generally offer a more comfortable ride, the thing you need most on an off-road vehicle is ground clearance; since the lowest part of a 4×4 vehicle is almost invariably the differentials, a solid axle will lift the differential off the ground and out of the way should one front wheel traverse an obstacle like a rock, or the raised centre of two-wheel tracks, of which much of the road system in Africa consists.
• Which 4×4 tyres?
It depends on where you are going and when you are going there; for instance, tyres for muddy conditions do not work well in deep sand and vice versa. You may have the best set-up 4WD in the world but using the wrong off-road tyres in the wrong conditions is inviting trouble. Off-road conditions in Africa are among the toughest in the world; therefore, plan your trip properly, especially with regard to the weather and its effects on the terrain you are going to be passing through.
• Angle of approach:
The angle of approach is determined by how much of the bodywork extends beyond the wheels. The less overhang there is, the better the off-road vehicle is able to engage steep hill faces and obstacles before the body work comes into contact with the obstacle.
Rock climbing or Saturday 4×4 Trails
Scrabbling over rocks and the steep cliff-like walls of ditches requires a 4×4 vehicle with huge wheels, lots of power and exceptional ground clearance, but most importantly, a short wheel base to prevent you hanging up on a rock or a steep hill crest. While lots of power is not necessarily a bad thing in an expedition vehicle, too much ground clearance can have a huge negative impact on the centre of gravity of a heavily loaded off-road vehicle. Not to mention the limited suspension travel because of the over-sized wheels.
Rallying or competition vehicles:
Competition with 4×4 trucks does not quite fall within the scope of this article, except to mention that as a rule, “soft” 4WD vehicles do not make good competition vehicles.
“Soft” 4×4 Vehicles
Answering to the needs and demands of a well-defined market segment, these are mostly luxury SUV and cross-over type vehicles and collectively they are all that “good” off-road vehicles are not; their 4WD systems, whether full- or part time, are mostly ineffective and many, if not all, die-hard off- road enthusiasts regard the 4WD systems on these vehicles as being less than useless for serious off-road driving applications and here is why:
• Bad suspensions:
Being set up for urban and highway conditions, these 4WD systems hardly ever offer sufficient suspension travel for serious off-road driving but apart from this, their settings, while comfortable for highway use, are too soft to handle the rigours of any but the smoothest terrain off the beaten path. Worse, from the off-road perspective, the independent suspensions of these vehicles, more often than not, do not give sufficient ground clearance.
• Bad transmissions:
Given their segment in the luxury vehicle market, these transmissions are mostly not equipped with a low range, which is an essential requirement for serious off-road driving.
• They are overly complicated:
There are no repair facilities in the bush, and especially not ones equipped with diagnostic computers to trace and diagnose electronic issues. Some SUV’s have several hundred fuses and relays that control everything from the sunroof to the suspension settings, and even some fuses that control other fuses. A collapsed air suspension cannot be repaired in the bush, nor can anything more complicated than replacing a wiper blade be accomplished without the aid of a diagnostic computer.
• Overly rigid body shells:
A crucial design element in any effective off-road vehicle is its ability to flex under extreme conditions, in order to help maintain wheel contact with the ground. This flexing can only be accomplished by using a step-ladder chassis or frame, and the unibody, or monocoque, construction of luxury SUV’s preclude the ability to flex, or deform.
• Limited load carrying capacity:
Even if you could modify and adapt a SUV’s suspensions to overland expedition standards, the overall weight of the vehicle is already such that not much more than three passengers with overnight bags could be accommodated with any degree of safety and/or comfort.
These are only a few examples of reasons why a luxury SUV can never be a good 4×4 or off-road vehicle. They are simply not designed for the role, and the vast majority of them will in any case never see terrain that could test their limited 4WD capabilities, or even just a gravel road.
There are of course many other considerations, not the least of which are your personal preferences with regards to which 4×4 type and configuration, but as a bare minimum, your chosen off-road vehicle should have a step-ladder type chassis or frame, a reliable and powerful power plant, a low range gear set in the transmission, a reliable and proven transfer case and final drives, and at least some of the basic safety systems such as ABS, Active Stability Control, Hill Climb and Descent Assist, and Roll over Warning.
All the points, and more, mentioned under the “Proper” 4×4 heading are what go into making a good and efficient off-road vehicle. Even within this broad field, it is impossible to say which 4×4 vehicle is sure to perform better than any other in any given set of circumstances. What is a 4×4 to you? 4WD vehicles and off-road driving is a highly specialized field and in the following articles we will focus more closely on issues of power vs. torque, engine choices, vehicle construction, pros and cons of various suspension and 4WD systems and configurations, safety systems, general driving skills and recovery techniques, and even off- road driving and nature conservation, and more.