When can I use '4H' in my new 4X4?

New to the off-road scene? Knowing how to use your 4WD is important. Using 4H to increase stability and traction needs to be done right…

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If you’re part of the off-roading fraternity, or you’re intending to join, it’s all about towing and using low-range four-wheel drive, and using all those rugged capabilities.

My first, and most important, piece of advice is - get training. Get proper, schooled off-road training. It’s the same as going to a racetrack. Nine times out of 10, the vehicle is more capable than you.

If you’re a racing professional, I’m not talking to you. But if you’re the owner of a new ute like a Ford Ranger, Mitsubishi Triton, Toyota Hilux or even a wagon like Pajero Sport, LandCruiser or Patrol, vehicles like this are designed with margins of capability and safety typically well above the ordinary driver - which is how you want it.

Learning how to exploit the in-built potential of your vehicle, as standard, is going to be much more affordable, and you’ll also improve your skillset to make you more proficient out there in the rough stuff.

Vehicles like this will go a very long way in standard trim. You don’t need to load-up at ARB, you need a software upgrade so you can do more with less.

Nonetheless, I got this question recently for a dude named Ben.

Okay, it’s important to get the numbers right around towing. I did a feasibility study around Ben’s situation, by looking at the GVM (gross vehicle mass) and GCM (gross combination mass), as well as the ATM (aggregate trailer mass), and the kerb weight of the Ranger.

Evaluating these weights, you are strictly limited by the Ranger’s 6000kg combination mass. Then you minus the trailer which, in this example, we’ll assume is 3000kg (laden), and that means the Ranger in its fully loaded condition cannot exceed 3000kg, for a total of 6000g. Dead empty (except with a full tank of fuel), the Ranger WIldtrak 3.2 auto weighs 2278kg. That’s in the ballpark of 2.3 tonnes and allows Ben 700kg of payload.

But then we need to do GVM analysis on the Ranger, which is strictly limited to 3200kgs, by the manufacturer. The payload of this Ranger, not towing anything, is 922kg.

So you need to assess - a three tonne trailer will mean 300kg of towball download, which the Ranger is carrying; it’s part of the GVM. Take the 300kg download off the Ranger’s payload, that’s leaving you 622kg.

Now, 622kgs seems like heaps, but if you add four people, their luggage, a towbar, the bullbar, a roof rack, fuel and water - it will add up very quickly and you are at risk of losing track of how much weight you’ve added.

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Can I tow safely using 4H?

Then there’s the crux of Ben’s question:

When you’re driving one of those old-school four-wheel drives, like a Ranger or Prado, with a simple 2H, 4H and 4L transfer case you’ve got an engine, a gearbox and a transfer case.

The transfer case is designed to put the vehicle in 2WD for most of its life, like Mum and Dad’s Commodore, for high traction surfaces such as bitumen and high quality gravel roads.

Then, when you need 4WD, it engages a front propshaft that goes down to two driveshafts across the two front wheels, and then you have 4WD.

The potential problem with doing this on a high traction surface is that there’s no relative motion allowed between the front and rear prop shafts, which is bad every time you’re not going dead straight. Why?

Every time you turn a corner, the front wheels travel further than the rear wheels. The front wheels want to turn faster, and the rear wheels want to turn slower.

Take any piece of tube, or even a stick. If you hold each end in each hand and move it straight forward, those ends take the same path. But if you turn the stick to the left, your left hand will move a much shorter distance than your right hand; you’ll get the opposite result turning the stick right.

Then, if you add traction to the situation, on all four wheels, there’s no outlet or release or transfer for all that relative motion in the shafts and the driveline. But that load has to go somewhere, and it will find the weakest link in that system, such as a constant velocity (CV) joint, or an axle in the rear diff housing, it could be the universal joint, or either of the front or rear propshafts - because they are all under additional stress from having 4H selected.

The only pressure relief valve is the reduced coefficient of friction under the tyres. If the  tyres can slip, it takes the load off. If not, you’ll break something.

And if you don’t break something, you simply grossly accelerate the wear rate of those components underneath.

I do not think it’s okay to engage 4WD on a wet, sealed road because you’re only talking about a 30 per cent reduction in grip, roughly.

The other problem is one called ‘scientific control'. There are so many variables when it comes to defining a ‘wet road’. A light mist of water across an otherwise dry road is very different in terms of available grip compared with an inch of standing water. There’s also an element of uncertainty around the grip levels when it rains after a week of 40 degree heat, where a light film of oil in the tar rises to the surface and effectively lubricates the road. That road could still be quite sticky and offer plenty of grip once it dries. There are too many unknown unknowns.

It’s the same situation for dirt roads. There are some kinds of good quality dirt roads which are just as grippy as sealed bitumen roads, but cost half as much as the blacktop to make, which is one of the reasons two-thirds of Australian roads are unsealed.

Then there are other dirt roads which are like ice skating rinks, covered in thick layers of fine bulldust or loose, dry gravel which never beds down properly and partially washes away after every downpour. In those dodgy dirt roads, obviously you want to engage 4H.

If you routinely operate a 4WD with one of those old-school tractor-style 4X4 system,s you may not necessarily break something, but you will rapidly increase the wear rate of those driveline components, and you can expect them to fail sooner. 

And there’s also an element of human error, where you might forget to switch 4H off, back into 2H, and upon making a sharp U-turn or something, you could easily break something then. And it’s entirely your fault - there’s no crying to the dealer service department and trying for a warranty claim. You’re coughing up the money.

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OPERATING IN 4H

To engage 4WD, when you’re one one of those dodgy dirt backroads where clearly grip is compromised, you generally want to do this on-the-fly. It’s very handy in these situations when you have a 4WD which has the capacity to engage 4H while moving.

You flick the lever or switch from 2H to the 4H position, and then some solenoids to the rest.

Pro Tip: If you have a lot of steering lock on at that moment, you probably won’t be able to engage 4H because the front and rear propshafts need to be at similar synchronous speeds before the mechanism can engage. This is important to keep in mind if you’re in 2WD and getting into trouble adding steering lock to correct a drifting problem, because 4H will not engage. Hence, you need to drive to the conditions and avoid getting into that kind of predicament.

Those shafts need to be rotating at similar rates in order to lock into place and engage.

And remember, if you break one of those crucial driveline components halfway to Dingo Piss Creek, it could be a very different kind of holiday and you’ll be waiting a long time for a tow truck.

The latest technology really helps. It really does, especially in the domain of safety, both in the caravan and the tow vehicle.

But, you also need to know technology is not a substitute for more fundamental protections you need to put in place.

There’s a worrying aspect of the human condition in psychology called ‘risk homeostasis’. It typically occurs when someone in a potentially dangerous position is given a hardhat and hi-vis safety vest, and their perception of risk remains constant in line with the level of safety involved. Put another way, people will tend to take more risk when they make themselves, or perceive themselves, to be safer. As if the addition of protection allows them to take greater or more risk of harm - hence the ‘stasis’.

Don’t buy a very safe vehicle and an equally safe caravan or trailer, and then increase your level of risk taking because you have additional features keeping you straight and narrow.

You have to continue driving conservatively, because that heavy multi-tonne caravan, being towed by that heavy vehicle, has a lot of acquired energy and the longer your on the road for your exposure to danger increases.

So, you need to treat the assignment with a safety system, as if you’re at work - checking tyres, keeping the weight down, driving ultra-conservatively, leaving plenty of time and taking regular breaks from paying constant, vigilant attention at all times.

I hope this helps you stay safe on the road to Dingo Piss Creek. Please, do not send a postcard.

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