Given that you now know how your 4WD works, how, then, do you drive it? A typical SUV should drive just like any other car on the road.
But what happens when the going gets sticky, quite literally, and the unbeaten path you chose to follow becomes intractable — and you are forced to use the supplementary hardware that other cars do not have?
Here are some dos and don’ts of piloting a fully-fledged off-road vehicle in conditions that would be difficult to traverse, even on foot.
1.When to use the transfer case: A typical 4WD transfer case is split into three or four: 2-Wheel and 4-Wheel drive modes; and High & Low (H and L).
Most new 4X4s have 2L done away with, leaving only 2H, 4L, and 4H.
The low gear ratios (2L and 4L) are used when extremely low speeds are required, such as when crawling over rocks, speeds that would otherwise stall the engine or require excessive clutch control in a car with a manual transmission.
Excessive clutch control not only wears out the driver, it is also very taxing on the clutch mechanism itself.
Low ratios are also needed in situations demanding massive torque, such as when ascending an extremely steep incline (up to 45° angle or 1:1 aspect ratio, usually impossible for most cars) or when pulling/carrying a heavy load.
The former demands 4L, while the latter could be handled in 2L. High ratios are used in normal driving conditions (2H), or when grip and traction are questionable but speed is not an issue (4H).
2. When driving on the road: Use 2H. High ratios allow normal driving speeds, and engagement of 4H is superfluous. It is advisable to disengage 4WD when driving normally as this reduces the rolling resistance of the transmission components through unnecessary friction, thus saving fuel.
3. When bogged down in mud: Engage 4WD. Depending on how unwelcome the pending quagmire is, use either 4L or 4H. 4L is used in especially messy conditions, such as very deep and very soft mud pits.
In this case, 4H spins the tyres fast and digs the vehicle deeper into the clag. 4L supplies the large amounts of torque needed to pull the vehicle out if, at least, one of the tyres suddenly finds traction. 4H can be used in muddy conditions where the tyres cannot sink into the mire, thus cannot dig themselves in.
4. When crawling over rocks: Use 4L only. Not only will you need to go really slow, but at some point one or two wheels will catch air, robbing them of traction.
You need traction in the rest of the running gear to keep yourself moving. Try not drive over crags and rocks with obstacles between the tyres, as they might snag the vehicle’s undercarriage and cause damage.
Instead, drive with the tyres rolling onto and over the obstacle. This maximises your ground clearance and prevents you from getting stuck or ruining your car.
In some dire cases, it might be necessary to use a spotter, or get out the vehicle yourself and chart a path on foot first before following through in your vehicle. The spotter also helps the driver manoeuver accurately over the many obstacles.
5. When going up a steep incline: You might not need 4WD for this if the ground being covered is not too treacherous, but you might need low gear ratios.
That means, ideally, that you use 2L, if your car is so equipped. If not, use 4L. The low ratios multiply the engine torque, thus enabling one’s off-road machine to surmount slopes of any severity.
Some clever drivers might try to weave left and right if the slope is extremely steep to reduce the severity of the climbing angle, but this is not always wise.
The vehicle’s weight is focused on the side facing downhill: if it shifts to one side rather than the back, you could easily tumble off your path and roll downhill. Remember that most off-roaders have high ground clearance — therefore a high centre of gravity — and are thus inherently unstable.
6. When going down a similarly steep incline: Whatever you do, do not touch the brakes. While this might seem counter-intuitive, application of the brakes will see your off-road expedition degenerate into a rollover fiesta that will cost you your precious SUV, and possibly your life.
When facing downhill, the weight of the engine makes the vehicle nose-heavy and causes the front tyres to press harder on the ground.
Applying the brakes throws even more weight towards the front and will make the vehicle somersault, or roll over if you are moving at an angle.
Engage Low, preferably 4L. Keep the vehicle in first gear, with the clutch pedal in the fully out position for manual transmissions, and let the compression resistance from a closed-throttle engine slow you down.
For automatic transmissions, snick the lever into first gear (1 or L, depending on the manufacturer). Engine braking rather than conventional braking is the way to go here.
7. When wading through water/fording a river: Ignore your manufacturer’s chest-thumping about how their vehicle can wade through 70 inches of running water.
They had highly skilled drivers do that, and what they can manage might not be within your capabilities. The safest depth to wade through in an SUV is about 20 inches (0.5m), though again this depends on your vehicle’s ground clearance.
A rule of thumb is headlamp-level depth (the lamps should be above the water line). If your car is fitted with a snorkel, you could sink deeper to bonnet level (lamps below the water line but the bonnet is above).
Try not to splash into the water, because if the water gets into the vehicle’s electrical system, you will have a really long day drying it out.
Keep the 4WD (4H or 4L) fully engaged when driving through water at all times.
You might be driving through water, but the bed is mud, rocks or both, remember. After crossing, dry out your brakes to recover lost efficiency (wet brakes are almost useless). This can be done by driving with the brake pedal lightly pressed for a short distance.