“A 4×2 with axle differential lock can do almost as much as, and can go just about anywhere that a 4×4 can go”. This statement, often used as selling hype on the showroom floor is untrue and misleading. The difference in the off-road ability of a high-clearance 4×4 and a similar 4×2 with axle differential-lock is dramatic. The difference in the off-road ability of a high-clearance 4×2 with differential-lock and a similar vehicle without differential-lock is also dramatic, but only under specific conditions. Why are these differences so vast?
Half the load, double the traction
A 4×2 transmission means that of the four wheels on the ground, two are driven. Therefore, 100% of the tractive force necessary to push the vehicle is divided between these two wheels. Add two more driving wheels and things change dramatically. The tractive force is now divided amongst four wheels instead of two, halving the load on each wheel and thus doubling the effective traction. So in the laboratory, when the terrain under the vehicle remains constant, a 4×4 has twice the tractional ability of a 4×2.
In the real world with rocks, grass, mud and sand challenging the grip of the tyres, things get even better for the 4×4, because the tractive qualities of the ground under each wheel are never equal or constant. For the purposes of this discussion, we will assume that the 4×2 has its rear differential locked and the 4×4 has no axle differential-locks.
For our 4×2 to move, one of its two driving wheels must lie on terrain that will support the tractive effort. If not, both driving wheels will spin. In the case of our 4×4, it will move if any one of the four wheels has enough grip to support the tractive effort, with the following proviso: should one of the wheels on any one axle lose 100% of its traction, the demand for traction is transferred to the other axle. For a moment the vehicle effectively becomes a 4×2, until conditions change. As the vehicle moves, conditions change by the millisecond, during which time traction is transferred from one wheel to another and from one axle to another. So, not only is the traction load split between left and right wheels, it is simultaneously split between back and front.
Another way to illustrate how these vehicles differ in ability is to ask how each driver feels about driving over difficult terrain. While the 4×2 driver moves along the trail he is concerned that conditions are going to get too difficult for him to continue. The 4×4 driver, on the other hand, is excited about the prospect that the trail will get tougher, and that his or her vehicle will be challenged. Yet another way of looking at it is to count the broken differentials that litter 4×4 trails. These shattered components mostly come from 4x2s that, having completed 80% of the trail and were asked to overcome a steep rocky climb that stood between them and an overnight stop. And so the driver, loath to turn back, throws caution and good sense to the wind and attacks the slope like a test pilot attempting a new climb-to-altitude record.
The reason for needing to rush the slope is the lack of low transfer gearing. Without it, the vehicle has no choice but to race. The trouble is, the high speed means that wheels bounce violently and the vehicle loses even more traction: it’s a vicious circle, the more speed, the less traction, which means that more speed is needed and so on. However, low transfer gearing means that the steepest, roughest slopes can be taken slowly, carefully and with little or no risk of vehicle damage. Extra low gearing is as essential to an off-road machine as is all-wheel drive. Without it, it is not an off-roader, nor is it particularly good at heavy-duty pulling: for example, low gearing saves clutch wear when pulling trailers up steep pull-aways.
Full-time four-wheel drive
It has been suggested that a 4×4 with an open centre differential is, by virtue of having three open differentials in the system, driven by only one wheel at a time. This I believe is misleading. In ideal traction conditions this type of vehicle is being driven by all four wheels simultaneously, with 100% of the traction effort being split 25% each. Moving on a smooth tar surface, a full-time four-wheel drive vehicle requiring a very modest 25% tractive effort on each wheel, experiences neutral cornering, even tyre wear and improved handling. This means that four-wheel drive is an important safety factor for any vehicle equipped with it, improving stability on gravel, better braking, overall safety and four wheels doing the work greatly reduces the impact on the environment.
Off-road, and even on gravel, the centre differential must be locked immediately, not just prior to tackling difficult terrain. Imagine a vehicle moving off-road with its centre differential open. It is still putting 25% tractive power to each wheel, a great improvement over 50% of a two-wheel drive, but this is not going to be maintained because the tractive requirements are changing constantly and the differentials in the system will cause the tractive power requirements of each wheel to change with the terrain. As one of the wheels loses traction, it will rob tractive power from the others by spinning free. Lock the centre differential and it then requires two of the four wheels to lose traction for the same to happen. Moreover, one front and one back must lose traction before tractive power is going to be absorbed from the other wheels. That is why the centre differential must be locked whenever there is a chance that the demands on the tractive effort may change, i.e. on any surface other than smooth tar.
Axle differential locks on 4x2s
The axle lockers offered on 4×2 high clearance pickups improves the vehicle ability over uneven terrain to an extent few would believe. The important word here is ‘uneven’, for it is on this type of terrain that the difference in the vehicle’s performance is dramatic, and nowhere else. For the differential lock to make any difference, the terrain must be the kind that will force one of the driving wheels to have insufficient traction to drive the vehicle. This happens when weight is taken off either driving wheel and occurs in all terrain where the suspension is moving with high vertical movements. If the ground is flat and there is similar traction on both driving wheels, a differential lock will have little effect. In some situations it can even decrease traction.
General vehicle selection questions
These are email questions directed toward 4×4 author, Andrew St.Pierre White, together with his responses. Please note. What is written here is only an opinion. He receives many requests for advice and he freely gives it. Much of this advice is also given from a South African perspective.
What are the most important things I should know before selecting a 4×4?
My answer is summarised in an article on this website called, ‘The Ten Golden Rules”. Click here.
I want a vehicle for driving through Africa. I love the Land Rover Defender and Discovery, but all the advice seems to point toward a Toyota. Why?
The overall reason why people suggest a Toyota is reliability. The overall reason why not to take a Land Rover product is reliability. It’s that simple. If you take a Land Rover (I have owned three spanning 18 years), you have an 99% chance of minor trouble, 60% chance of major but repairable trouble and a 25% chance of major trouble where the repair is lengthy and expensive and difficult to get spares when needed.
With a Toyota (assuming it’s not an old clap-trap) the probability is a 50% chance of minor trouble, 10% chance of major but repairable trouble and a 1% chance of major, major trouble. Although Land Rovers spares can be found, Toyotas are so common, spares are a lot more easily found.
This maybe a gross generalization, but I invite you to go online and read about trans-Africa journeys. Those where a Land Rover is the vehicle of choice, the vehicle is given a name, and tends to make itself, its preparation and maintenance a significant part of the story. On the other hand, if there is a Toyota Land Cruiser involved, it’s often well into the story until it is revealed often by the photos, that is a Toyota involved. It’s as if Land Rover owners participants wish the vehicle to break down so that they have something to write about. The Toyota operators tend to focus more on the places, people and experiences, because the vehicle rarely is even mentioned or thought about.
Yes, Defender has the image and the looks, which no Toyota can even come close to, but performance wise, the Defender is a station-wagon but rides like a truck, comparable to the Land Cruiser FJ series, which is Toyota’s pick-up based chassis. Neither are comfortable and uprated shocks and springs on both are advisable. If you want a Land Rover, then Defender is the only real option, or an older Discovery or very old Range Rover. With Toyota there are a few more choices: The 80-series and 105 series wagons are brilliant in every respect. Ugly but brilliant. The 100VX is okay but soft and the new Discovery has got so much delicate electronics, it’s also, sadly, not a good choice. I simple thing like a broken air-bag sensor can leave you utterly stranded and only a Rover agent with a laptop can get you going again. Scary thought!
Most Land Cruisers (not VX or V8 100-series) are simple with few mechanical frills, they are built so they can be repaired and don’t fall over as easily. But they are cost much more, it’s sometimes embarrassingly so. Unlike Land Rovers, Land Cruisers are built to be overloaded. That’s why they are the no.1 choice with aid organisations. (Aid organisations love Cruisers first. They also like Nissan Patrols, Mercedes G’s and the Suzuki SJ is very popular. Sadly, Land Rover isn’t high on the list any more. (They used to love old Range Rovers because you couldn’t kill them)
If you want to go the Land Cruiser route, I suggest calling Stuart Baillie. He is an expert on all the models and can fit some extras if you need them. Tell him I sent you. Stuart is a trustworthy individual who will not give bad advice just to make a sale. He’s that sort of chap (011) 702-2149
Just my opinion. Hope this helps Andrew S White
Does the number of plies in a tyre side-wall really matter? I hear the BF Goodrich AT is so good, but more expensive. I see many other good-looking tyres but they all have a 2-ply sidewalls. Is this important?
Sidewall thickness is important, no doubt about it, but as good as the BF Goodrich ATs are, there are others just as good. The trouble with tyres is that one user will find good performance in a tyre while another, even driving the same kind of vehicle, may find different. For example. I drove Continental Conti-Trac At tyres through the Kaokoveld. Some who know the area suggested that the tyres would be destroyed by the trip. Well they handled it well, with just one puncture and no other trouble. My vehicle was a Mercedes 290GD with automatic transmission and I have a gentle driving style; two ingredients that protect tyres. Conti-tracs have 2-ply sidewalls and has never earned a reputation for toughness.
Sidewalls that have a block shape, as opposed to rounded, tend to protect themselves better as the shape deflects obstacles as the tyre rides over them. A rounded crown will permit sharp objects to penetrate or damage the sidewall even from underneath. Such a tyre is the Bridgestone Dueller 695 ATs and I ran them on my Mercedes G for about 40 000 kms without a puncture and I was impressed with them. This all ended when in 2008 crossing the Kalahari these tyres disintegrated for no explainable reason. Since then I have lost faith in this product.
During a 27 000kms film shoot in 2010, running 3-ply sidwwall BF Goodrich AT, 265/75 R16 tyres I had not a single puncture. In all my years of off-roading, I have never had such outstanding performance from a set of tyres. Back on my early days, 10 punctures for such a trip would have been expected. How far we have come!
Hope this helps Andrew S White
I have about R120 000 to spend on a use 4×4. I would like to travel to outback regions and do weekend 4×4 trails. I have a family and need space. What suggestions do you have?
I will highlight a few vehicles that you will find in your price range:
Land Rover Defender with the 200Tdi or 300Tdi engines.
If they are well looked after a good choice. If they have a history of engine changes, don’t trust them even if the engine is brand new: this spells danger. Defenders can be troublesome so if you are the type who cannot work on a vehicle yourself and must send it to the agents when something goes wrong, a Defender is going to be very expensive to run. If you love working on your vehicle yourself, a Defender may keep you quite busy. Good load carrier, not very comfortable on the open road, back seat passengers complain about the seating. Overloaded roof-racks make the Defender dangerous as roll-overs are common. Max permissible rack weight is just 75kgs. Many say things like, “I have loaded it with 150kgs and not had a problem”. Ignore these claims. They may be true, but it’s only because these people have never had to take emergency action with this load on the roof. It’s the unforeseen emergency that rolls Defenders. And when they do, the roof flattens like a frisby. Great vehicles for dressing up and always look good, even if they are battered and bruised.
Toyota Hilux. Late model with the solid axles.
Unbreakable, very reliable, thirsty, uncomfortable, go on forever, inexpensive to run but for high fuel consumption, Must change suspension to make them comfortable and the standard fuel tank is tiny. Nothing beats it for reliability and longevity.
Toyota Land Cruiser FJ60 (This is the Cruiser station-wagon with the leaf springs)
Thirsty and a bit heavy to drive. Older vehicles must have bushes replaced and the steering slack seen to, otherwise very tough. Fairly comfortable on the long run, have high resale value and it’s easy to see why. Big and ugly but immensely practical.
For the most part the G is wonderful. Trouble is, they are so rare. Reliable, spares are not a problem as some think. The 300D, 230G and 260G are all dogs! Underpowered but extremely robust – so robust they make a Defender look like a Lada! Built like a Tiger Tank. Handles only a little bit better; I’m kidding!. Handles on and off road better than a Defender: less body roll, carries a load as well, more comfortable, steering not vague, much, much tighter turning circle and, you can put 200kgs on the roof! Off-road, beatable by nothing except especially-modified challenge vehicles. 3-door models are to be found, but 5-door LWB versions command a higher price and are extremely rare. There are a few 1990 5-doors models about. Grab it if you see it. There are engine mods that can make it go a bit quicker. Auto gearbox is preferable to manual, but you may not have a choice. Be the first to buy Auto-trader every Thursday and be ready to get in your car with your cheque book. It’s the only way! If you want the rugged style and image of a Defender but want a more reliable beast, the G is the ONLY option.
Range Rover – the first one
Of all the cars in this list, if you are just starting out and have little cash, buy an old, hopefully loved, Range Rover. They will keep you a bit busy keeping it going but they are cheap and fun, fun, fun. Excellent off-road and good on. Doesn’t carry a load particularly well and being a Land Rover, not that reliable. But really inexpensive, the V8s go forever but the gearboxes can be troublesome. Don’t look for a diesel version: They were built in small numbers with a Land Rover 100Tdi engine. This engine is a disaster and isn’t suited to drive any motor car, let alone one suited to travelling into the outback. I cut my teeth in a 1971 Range Rover and still love them to bits.
Off-road they lack clearance, and can break if over-loaded. Very inexpensive to run, good fuel consumption and reliable if you can find a well maintained one. Good people carrier and altogether excellent, but a bit boring.
Land Rover Discovery – first model
Excellent value for money because they do not have a good resale value, prices run well under R100K. Cramped in the back, hardly any load space, this is maybe the world’s only five-door, two-seater! Good fun off-road and the V8 is a nice drive but a bit thirsty. V8 reliable, auto box good, manual gearbox troublesome over 150 000kms. The diesel models are more expensive, frugal but underpowered. Expect to have the turbo replaced. Diesels must have the idler-pulley bearing modification. If not, a huge engine repair bill is waiting when it breaks. Great as a hobby 4×4 – cheap, easy to work on, lots of fun.
Lada Niva, Asia Rocsta, Mahindra etc
These are cheap and nasty, none very reliable and only the Lada is any good off road, when it’s running that is. Spares can be very difficult to find because each of these has had so many importers, none of which supported their vehicles well.Cramped, noisy and generally horrible. Leave it at the dealers: You can do much, much better.
Should I buy a trailer? I don’t really know if it’s going to be too much of a burden.
I am going to be biased answering this one because I prefer not to pull a trailer. Those who do, who do not travel the really difficult routes, love them and use them year in, year out.
The advantages are:
More space, more payload and more range. (Payload means range. The more fuel and water that can be carried the longer the range.)
Living ease. “Roughing it” is no longer an apt expression.
Leave your ‘kitchen’ in camp when going on game drives etc.
The disadvantages are:
You take things you do not need and can do without, because you can.
When going gets tricky, can really become a burden. An example may illustrate this: On the banks of a river in Zambia. The rains come down all night. The following morning when trying to leave, the vehicle is unable to pull the trailer up the slope and off the riverbank. (This actually happened. Only the Merc G could haul its trailer out, so it went down six times and hauled five trailers and one Discovery up the bank)
Less space for less stuff… no kitchen sink
If it breaks, and the badly packed or badly built ones do, you will be stranded.
Roof-top tent or ground tent?
I summarise it like this:
Roof: Secure from wild animals, to a point. A rapid evacuation from the area is not possible.
Ground: Less secure from wild animals although they are not a real danger, more a perceived one.
Roof: Secure from insects and scorpions. Security from mosquitoes depends on tent quality.
Ground: Keeping the flap zipped up is more important. Security from mosquitoes depends on tent quality. Some are NOT good.
Roof: Even the large ones can only sleep two adults, and even then it’s cramped, cramped, cramped. Even tying your shoelace inside is an ordeal. Leave the bags inside the vehicle. (Biggest disadvantage)
Ground: Tents advertised as 3-man bow tents can easily accommodate three adults and their bags.
Roof: Takes a shorter time to erect, perhaps 20%.
Easy to unpack, a real pain to pack up and return to its cover Roof: Must be collapsed and packed away fully before the vehicle can be moved, for a game drive etc
Roof: If the ground is not level, the vehicle can be made level with rocks etc.
Ground: If there is no level ground or it’s covered with rocks, too bad! (Unusual)
Roof: If you move around a lot, the vehicle rocks to and fro. Warmer The ground can be very hard and cold.
Roof: The mattress and sleeping bags can be left inside as the tent is folded away, saving space in the vehicle. This is by far the biggest advantage.
Ground: Tent must be emptied when packed away
Roof: Heavy. Reduces remaining weight permitted on roof. Lifts the centre of gravity. Significant increase in fuel consumption at high speeds. In comparison, lightweight and can be carried anywhere