Under the big 4WD’s bonnet

Once upon a time, off-road driving was a favourite and much respected pastime for Kenyans. Lovingly referred to as “bundu-bashing” by pundits, a good number dismissed it as the preserve of the well-to-do — which it was — but that did not make it any less fascinating.

Over time, economic complications and crowded lifestyles have seen the activity lose enthusiasts, down to a few die-hards.

Also, the alleged complication of driving a 4WD vehicle off-road (and the accompanying jargon spoken by the few die-hards) does not provide the appeal this activity deserves.

Well, all that is set to change. While I will not necessarily buy you a brand new 4WD car, I will still do my best to generate interest in this almost-forgotten hobby.

Those that have experienced the Rhino Charge, either as spectators or contenders, know just how much fun off-roading can be.

But, first off, let’s demystify the terminology involved in the off-road world.

Transfer Case: This is a secondary gearbox in a typical 4WD car. It is usually controlled by a smaller lever in the centre console of the car, usually next to the main gear lever, though some advanced 4WD cars have an automatically controlled unit.

While the primary gearbox apportions gear ratios (1-2-3-…), the transfer case does two things: it splits drive into either two or four (2WD or 4WD), by channelling power to either one axle or both.

The transfer case also splits the gears further into either high or low ratios (L or H). High ratios are for driving under normal or close to normal conditions, while low ratios are used when massive torque, rather than speed, is required.

So, what is this torque?

Torque and Power: Torque is the twisting effort applied by the engine on the drive-train. It is what enables the engine to pull a given load. It is also what will get you up a steep hill without too much struggling.

Power is the rate at which the engine works, or the amount of work it can actually do in a given time. In a nutshell, torque is what gets you going, and will determine the kind of load you can haul; while power is what keeps you going and determines the absolute speed at which you can move.

Traction and Grip: Traction is the capability of the tyres to provide motion. When skidding or slipping without the vehicle moving (or moving contrary to the direction in which the wheels are pointing), the tyres are said to have completely lost traction.

Partial loss of traction is where the tyres spin very fast but the corresponding movement is not in direct proportion. Grip is both the forward and sideways surface-hold of the tyres, and is what limits the vehicle from spinning wildly on loose surfaces or going sideways instead of forward.

Traction will keep you moving in slippery conditions, while grip will keep you clinging to the slippery slope or on the road through a slippery corner, instead of slithering to your doom.

Locking/Lockable Differential (Diff-lock): The differential of a car is the “middle-man” between the gearbox and the wheels. This device allows the wheels on both ends of an axle to rotate at different speeds, such as when cornering, but sometimes, when the going is slippery, this is not the most desirable outcome.

To prevent one wheel from spinning wastefully, 4WD cars have a “diff-lock”, which basically locks the two tyres on the same axle together and forces them to rotate at the same speed.

Precious torque is then not wasted away by one tyre spinning. In some cars, the diff-lock is engaged using a button or a lever, while most new-fangled SUVs engage the diff-lock automatically whenever 4L is selected.

Driving with the diff lock engaged, especially for the front axle makes, cornering extremely difficult and uncomfortable. It should be used only when necessary.

(Explaining the exact modus operandi of a differential lock might consume more space than I am allocated here).

Locking Hubs: Also known as free-wheeling hubs, they are an accessory fitted to many four-wheel drive vehicles, allowing the front wheels to rotate freely when 4WD is not in use.

The idea was to keep parts that were not needed in 2WD from rotating in order to reduce drag/friction — and thus save fuel — while at the same time minimising wear and tear on front axle components.

With unlocked hubs, one also gets a quieter, smoother ride. Experts, however, question whether these benefits are real or imagined.
In older vehicles, manual locking hubs are used.

This requires getting out of the vehicle to engage or disengage the front wheels by hand. In more modern 4WD vehicles, automatic locking hubs are often used, which, as the name implies, engage automatically when 4WD is activated from inside the vehicle.

The main advantage is that the driver does not need to leave the vehicle to activate 4WD, but the disadvantage is that most designs require the vehicle to move some distance (usually a whole wheel turn) in order for the hubs to engage or disengage (in many cases 4WD can be engaged with the vehicle in motion).

This might not be possible if the vehicle gets completely stuck before engaging 4WD, so automatic hubs require more caution on the driver’s part.

Snorkel: The snorkel in a 4WD car works the same as that used by swimmers and divers: it enables underwater breathing.

While the divers’ instrument is a small neat device, its automotive equivalent is a huge, black round or square-topped tube attached along one of the bonnet flanks (the front fenders, actually) and rises to a level slightly above the roof-line.

One end (the one above the car) draws in air from the atmosphere while the other end is attached to the vehicle’s air-cleaner.

The snorkel thus forms a water-tight path for air to get into the engine.

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