What is it?
Do you need it?
When is it beneficial?
Diff-Lock & Traction control
Which is best?
What about a Limited Slip Diff?
Is it important?
How much is enough?
AWD vs 4WD
Are they really different?
Mud-terrains vs All-terrains
We’ve touched on this topic before, but to recap: low-range gearing is nothing more than a second gearbox that runs alongside your vehicle’s “normal” transmission − manual or automatic.
This reduction gearbox uses a step-down ratio to convert engine speed into low-revving torque. Thus, you’ll often see a vehicle’s low-range specifications listed as a ratio, such as 2.7 to 1.
What this means is, there’s a vast difference in torque performance between a low-range-capable vehicle, and a vehicle without reduction gearing. The extra low-revving torque not only makes your 4x4 better equipped to tackle rocks and steep gradients, it also dramatically improves the ability to descend a steep slope.
When it comes to off-road driving techniques, you generally want to avoid (as much as possible) using the brake pedal on a steep slope. The reason for this is that depressing the brake can lock the wheels and cause your vehicle to go into a slide. Once your tyres have lost traction, you have no means of steering the vehicle.
Low-range allows you to navigate steep declines by using engine compression and reduced gearing (instead of the brakes) to keep the tyres turning and safely responding to steering inputs.
DIFF-LOCK & TRACTION CONTROL
Essentially, these do the same thing, which is to maintain traction with the road. The moment you lose traction, you are either standing still, digging your vehicle into more trouble, or uncontrollably sliding.
The problem starts with your vehicle’s differential. Most conventional diffs are designed to allow for speed variations between two wheels. In other words, when you drive your vehicle around a corner the inside wheel is rotating at a different speed to the outside wheel.
While this feature is essential on-road, it’s generally a limitation off-road – where a loss of traction can suddenly occur.
The moment one wheel loses traction, the differential transfers the vehicle’s drive to the tyre with the least resistance (the one without traction). A diff-lock does exactly what its name suggests: it locks the diff in an equal torque split, so that no matter what the terrain, at least one wheel will always have traction.
Most standard-fit diff-locks are electro-mechanical, in that they use an electronic switch (or magnet) to engage a mechanical lock (or coupler). Diff-locks are usually bulletproof in design and construction, so they seldom give trouble and almost always do what they need to do. Traction Control (TC), however, is slightly more complicated.
TC systems use a vehicle's Anti-Lock Braking System (ABS) to “monitor” for wheel spin. The moment a lack of traction occurs (and a wheel spins uncontrollably) the TC system will detect the slippage and apply a brake force to the spinning wheel. This allows the differential to redirect torque to both wheels.
The fundamental difference between a diff-lock and Traction Control is that the former is proactive, while the latter is reactive. What’s more, TC systems are very often electronically complicated, and in most scenarios, they’re not as effective as a diff-lock.
Limited Slip Diffs (LSD) are another traction-aid option. They’re very reliable, mostly mechanical, but they tend to have a limited lifespan. What’s more, they’re not nearly as effective as a diff-lock.
Most double-cab pick-ups are equipped with a rear diff-lock as standard, but some vehicles, such as the Land Cruiser 70 Series, Jeep Wrangler Rubicon and Merc Gelandewagen, come fitted with a front and rear diff-lock. These vehicles are widely considered to be some of the best and most capable off-road machines on the market.
Arguably, the most important feature of any 4x4. An off-road vehicle can be fitted with the greatest suspension, top of the range tyres, and diff-locks front and rear – but without suitable clearance, it all counts for nought.
Clearance relates to four things:
- Approach angle
- Ramp angle
- Departure angle
- Ground clearance
As we all know, a chain is only as strong as its weakest link. And that applies to clearance angles, too. A vehicle with a great approach angle will do well at attacking steep slopes, but that won’t count for much if the vehicle’s tail snags halfway through the ascent.
Similarly, a good ramp angle (the clearance between the front and rear axles) is crucially important, and plays a vital role when climbing up (and over) rocky ledges and steps.
So, what is a “good” clearance angle? And what is a “bad” clearance angle? While it may be possible to determine the exact numbers, it hardly seems necessary as you should be able to visually gauge if a 4x4 has enough clearance to tackle a particular terrain. In other words, common sense is more important than specific figures and angles.
Lastly, some of the clearance angles, specified by certain vehicle manufacturers, are questionable at the best of times.
AWD vs 4WD
Strictly speaking, an All Wheel Drive (AWD) vehicle is not a 4x4, and no self-respecting off-road enthusiast would make the mistake of calling it that.
In simple terms: an AWD vehicle is a car that automatically distributes a percentage of the drive to the front and rear wheels. AWD vehicle owners often make the mistake of thinking that they own a 4x4 capable vehicle, and as a result, they push the boundaries of what the vehicle is designed to do. Examples of this can be found all over the internet, where you’ll often see Subarus, Audis and even AWD Ferraris stuck on sandy beaches.
Simply put, a 4WD vehicle is one that locks a centre diff or transfer case so that 50% of the vehicle’s drive goes to the front, and 50% to the rear.
We’ve covered the subject of traction already, but in the case of tyres, you want to match the tread pattern to your most relevant application. In off-road tyres, you’re looking at two categories: all-terrains and mud-terrains.
All-terrain tyres are designed for a wide variety of terrain types, however, they’re predominantly engineered for on-road use. You’ll often hear ratios of 70/30 or 60/40. That is, the tyre is designed for 70% on-road performance, and 30% off-road. So, an all-terrain tyre is a great option if you want to retain most of your vehicle’s on-road safety and comfort performance, while enjoying a touch of off-road prowess.
Mud-terrain tyres swing the ratio the other way; here, a ratio of 80/20 is common. (80% off-road and 20% on-road). Actually, the term mud-terrain is a bit misleading as it implies that the tyre is specifically engineered for mud. Although that may be true on some level, the term is more anecdotal and not directly specific to mud. The thing to remember is that most “mud-terrains” are simply tyres with an off-road bias, suitable for very loose terrain types such as rock, sand and mud.
Photo credit: Expedition Portal
However, the subject of tyres is vastly more complicated than just “all-terrain versus mud-terrain”, and unfortunately, it’s a subject many 4x4 owners get wrong by purchasing a set of lightweight Passenger tyres, instead of opting for the more robustly-built Light Truck (LT) alternative.
In an upcoming blog we’ll look at some key features of tyre construction and how it relates to your off-road tyre needs. So, if you’re in the market for a new set of takkies for your truck, you may want to hold out until then.