In our last two Tech Talk stories on All About Four-Wheel-Drive, I discussed what makes a vehicle a 4WD/4×4 and also the multiple differences between AWD and 4WD/4×4. Today, in this story, you will learn in detail about two of the most talked about “technical terms” in the world of 4x4s and offroading.
The motive of this series is to help you better understand not only the basics of offroading and 4x4s, but, in the process, also give you a good idea about your current or potential 4WD vehicle’s ability AND limitations so that you can use it effectively and happily offroad without damaging any of its components.
ARTICULATION
You must have heard this one a lot. The sad part is that the majority of reviewers don’t actually know themselves what articulation is. That’s why you don’t see them articulating the subject of articulation well. Today, I can promise you that I will break it down for you, as always, in an easy to understand language.
Simply put, articulation is the vehicle’s ability to keep all four wheels on the ground when the ground/surface is uneven. See, on a flat surface any car will be able to keep all four wheels on the ground, but that’s not the case offroad. Before I proceed further, please note that in this entire series—including this story, obviously—we’ll always be talking about driving slow, say, from 0–40 km/h. In fact, most hardcore offroading is done at single digit speeds, between 0–9 km/h, but there are some obstacles which require you to increase the momentum.
This is important for you to understand so that at least henceforth, while reading every story of this series, you visualise the vehicle being driven at the aforementioned ultra-low speeds. At high speeds, even the best hypercars can lift a wheel or two, and that naturally allows me to continue from where I had left before starting this long disclaimer.
I had mentioned that while any vehicle will have all wheels on the ground on a flat surface, offroad, that’s not the case. You might have seen endless offroading videos and images in which the majority of “SUVs” are shown tackling an obstacle where one wheel goes in a ditch and the other three wheels go up in the air, right? That’s NOT articulation. That’s LACK OF ARTICULATION. Unfortunately, most manufacturers’ marketing teams and the photography/videography agencies hired by them find those dramatic shots quite appealing while being completely oblivious to the fact that they’re highlighting a negative through such antics. Most offroad-punk owners are culprits too, but that’s a topic for some other day. For now, we’ll get back to articulation.
So you just learnt that if one wheel goes in a ditch, causing one or more wheels lose contact with the ground, that’s not articulation but a lack of it, and if the other three wheels remain on the ground too, then THAT’S called articulation, right? Great. You’re getting the hang of it now.
And why is it important, you ask? Well, it’s sheer common sense but I shall explain it anyway. Also, in case you’re wondering, I will talk about solid axles and sway bars under “suspension” in Part 4 of this series. For now, it would suffice to say that as far as stock production vehicles go, it’s the Jeep Wrangler Rubicon that has the best articulation in the world. Keeping the current production vehicles aside, you may also see the pictures of my Willys CJ-3B demonstrating incredible articulation.
But, again, your question was why’s articulation important? It’s important because with all four wheels on the ground you would have better traction than you would with one or more wheels off it, right? And TRACTION, dear ladies and gentlemen, is what you would always want to have offroad (onroad too; except while drifting, but, again, we’re talking about driving slow). Traction is what every bit of 4×4 hardware and software aims to enhance. Traction is the end goal. Period.
In life too, being grounded helps you go further. But how do those three-wheels-in-the-air SUVs come out of that obstacle, then? Well, they do it by either locking the differentials or by electronically “simulating” the effect of a locked differential and sending power to the wheel that has traction. You’ll learn all about it in the next section.
DIFFERENTIALS: OPEN VS LOCKED, BLD VS PROPER LOCKERS
All cars powered by internal combustion engines have at least one differential—a mechanical device which allows the powered wheels on the same axle to rotate at different speeds when the vehicle is taking a turn, etc. Such a differential is called an “open” differential. Most road cars come with open differentials and while they work great on the road, off the road they pose a serious limitation. Without getting into the internal components of a differential at this stage, let me just tell you that the primary function of a differential, which is to allow the wheels on the same axle to rotate at different speeds, becomes a weakness off the road when one powered wheel loses traction. All the power then goes to that wheel, which is spinning freely, and you’re stuck. Enter the locking differential.
In simple terms, a locking differential is essentially an open differential with some kind of a locking mechanism that “locks” the axle half-shafts together making them rotate as one unit, thereby turning both wheels at the same speed. That “locking” can be achieved through various mechanisms, which I’ll discuss in the advanced stages of this series. For now, you just need to understand the basics.
Therefore, the crux is that you have open differentials in most cars and even in some proper 4WD vehicles, but a few may have some kind of locking mechanism built into them providing partial/limited or complete locking ability, thereby earning them the term “locking differentials” and distinguishing them from their more common brethren known as open differentials.
For example, while the Jeep Wrangler Rubicon and Force Gurkha have proper selectable “lockers” that allow you to lock the axle half-shafts completely as one unit BEFORE entering the obstacle, the now-discontinued MLD (Mechanical Locking Differential) on the Mahindra Thar functioned more as an LSD (Limited Slip Differential) allowing for “limited slip” (100 rpm difference between both wheels on the same axle) before automatically locking the axle half-shafts and then unlocking them when both wheels regain traction. There are viscous coupling LSDs as well that never achieve 100 per cent locking, but like I said earlier, all that and more will be covered in the advanced stages of this series.
But I must tell you a bit about BLD (Brake Locking Differential), which simulates the effect of a locked differential without any actual “locking” happening in the differential. The Thar and Jimny both have it and its working is also quite simple. In four-wheel-drive, whenever the system senses a difference of 100 rpm or thereabouts in wheel speed on the same axle, it brakes the freely spinning wheel, thereby automatically directing power to the wheel that has traction. However, again, unlike proper lockers, and just like the MLD, the driver doesn’t have any control over it. BLD works AFTER a wheel slips / loses traction. With proper lockers, you have the advantage of locking them BEFORE entering an obstacle where you think you’ll spin a wheel or two otherwise.
I should also add that you must NEVER lock the differentials on hard surfaces. In fact, you would never make that mistake in the first place if you know that you must never engage 4H or 4L on hard surfaces in any of the vehicles mentioned in this story.
The Rubicon does have a 4H Auto mode where you can, and I had addressed that in part 2 of this series published last month (on the 22nd of January).
I would suggest that you read that as well, please, in case you missed it.
In Part 4 of this series, I would talk about suspension, and if it doesn’t take up the entire page, I might also discuss approach, breakover, and departure angles. Until then (and forever) please don’t jump dividers in your 4x4s unnecessarily. It’s neither cool nor impressive.
Also, do let me know what else would you want to know in this series. Write to me at [email protected]
