4WD guide to rocky roads

No terrain will make you marvel at what a 4WD can do than an undulating, steep rocky trail.

Here is something you’d think would be impossible for a goat to climb, and yet there’s a 4x4 wagon or ute successfully clambering up the track, axles akimbo.

How did they do it – and how can you climb such a trail and not end up being a star of a YouTube 4WD fail video?

The terrain we are talking about is anything that gets axles crossed up, which can vary from quite mild bumps and lumps in the trail to mad rocks and boulders, such as the boulder-hopping tracks on the Rubicon Trail in the US.

Knowing where to steer your 4WD and with how much speed in such conditions is something you have to learn.

Getting some 4WD driver training is the best way to obtain such experience quickly and effectively.

There are 4WD driver training courses operating within a few hours of most capital cities, and the experience you get doing such a course will be an invaluable leg up.

Not only is training a good idea before you go off to cross axles on rocky track, but also have a vehicle prepped to do it.

There is a lot of difference between 4WD models in how well they cope on rocky trails, particularly when driven straight out of the showroom. Some are naturals at it; others not so much.

Almost all stock-standard new 4x4 models can benefit from a suspension change that improves approach and departure angles and ground clearance.

There are legal limits to what you can do with height increase, so check with the road authority in your state or territory, but generally a lift of 50mm is the maximum permitted. Even this can make a noticeable improvement in underbody clearance on a rocky track.

The right tyres can make a big difference with rock-hopping. Ideally, you would have off-road tyres with a mud-terrain tread pattern, with large separate tread blocks and shoulder lugs that extended well down the tyre sidewall.

Even a set of All-Terrain tyres with their more open tread pattern (more open than Highway Terrain tyres) will make a big difference to grip.

Also read: Five of Australia's rockiest roads

If you have an old-school 4WD with just a limited-slip rear differential, you might find it’s not enough to make easy work of rock-hopping. While some oldies have excellent axle articulation that can in part make up for this, ultimately you may find you still need better traction gear.

The best mechanical traction device in a 4WD is an across-axle differential lock, either of the automatic type or manually engaged. Some new 4x4 off-roaders, such as upper-spec dual-cab utes, now have a rear diff lock as standard.

For true four-wheel drive and therefore the best traction (assuming you also have grippy tyres), an aftermarket front diff lock can also be fitted.

However, you might find that a fairly recent 4WD with a good electronic traction control set-up will be plenty.

Traction control is designed to work best in situations where it operates for a relatively short burst, then has a recovery period, so that the pump can build up hydraulic pressure again. This can suit negotiating a rocky trail quite well, as with most such tracks momentum and speed will not work. You have plenty of time.

Vehicles can get their underbody stuck on rock shelves or in crevices or holes on a rocky track. It’s usually on a tight access trail, so getting another vehicle to pull the stuck vehicle out is difficult. This is where a winch can save the day.

Winch kits include shackles, but you should add some extra ones, as well as a winch extension strap and some cable clamps, in case of a broken cable you need to repair.

On some steep, rocky tracks, you will need to do some road-building when a vehicle is stuck. A small aftermarket hydraulic bottle jack is a quick and easy way to lift the vehicle so you can place rocks and so on under the tyres. It’s also light and compact for storage.

Do not get under any vehicle that is in any risk of slipping.

The other option is a high-lift jack, which is a much bulkier and heavier (as well as expensive) recovery item, for which you will need correct jacking points to use.

But it has the advantage of not requiring you to crawl under the vehicle to set it up like a bottle jack.

It’s important to ensure that everything on your 4WD is ready to tackle a difficult section of rocky track before you head out into the wilds.

If you get serious about traversing rocky tracks, you soon find that underbody damage is part of the deal. If your 4WD has good underbody protection and you are not driving it like a madman, all the damage you do will likely be cosmetic.

However, if the standard protection plates are not up to it, they might need to be replaced with stronger aftermarket ones that can withstand the weight of the vehicle.

While tubular rock slider steel side steps are intended for rock hopping (and can be a good accessory to fit if you intend to do lots of it), fancy aluminium side steps are not. They are only meant to make it easier to climb in and out of a tall 4WD, and will fold up like a squashed aluminium can on a boulder-strewn track.

So, take them off before doing any serious trail driving.

Another part to take off is the tow ball tongue, if your 4WD has one, as it will easily get caught when climbing over rocky tracks.

The centre diff should be locked as soon as you’re on loose, steep ground, but don’t wait until you’re wedged on a rock or jammed in a track hollow before engaging your across-axle diff locks, if you have them.

An across-rear-axle lock should always be engaged before attempting demanding terrain, unless you have to make some very tight turns with momentum involved.

A locked rear diff will tend to steer you straighter than you might like. This will be obvious even when crawling over difficult terrain, and only exaggerated with any more speed on board.

Be very careful with throttle applications if side-sloping on rocky terrain with a diff-lock engaged. Nothing is more likely to follow the laws of gravity – that is, to slide or bounce sideways – than a diff-locked 4WD spinning both wheels on an axle.

As soon as you’re over the obstacle/s you’re negotiating, you should disengage the diff lock.

A front diff lock when engaged has a far more pronounced effect on steering than a rear diff lock. If you have a front diff lock, engage it only if there are no (or only very slight) turns involved, and disengage it as soon as the difficult rocky section has been climbed over.

With some experience you will be able to better gauge what the vehicle is doing and appraise a rocky climb and choose the best angles to negotiate.

Speed is not needed on most rocky trails, where being smooth and slow usually provides the best progress.

Rock climbing is usually done in the lowest gear you have and at a crawl. That’s not to say momentum is not necessary, just that the momentum is much more selective and there’s less of it.

Judicious application of the throttle at the right time can make a big difference between popping over a boulder-strewn track and wheel-spinning on it.

Don’t go for big hits of throttle and back off, as the backlash on relatively hard terrain such as rocks can end up doing damage to the drivetrain.

Remember, too, that while you think speed (or more momentum) might be the answer, it can create new problems. These include damage to steering, suspension differentials or underbody as the vehicle’s suspension is compressed and components end up being thumped over hard rocks.

Don’t try to run standard road pressures when you’re climbing over large stones and rock shelves, but you’ll need enough pressure to ensure the tyres can’t spin on the rims and to keep the sidewalls from flattening out as they encounter rock edges.

Try reducing tyre pressures to about 25psi to see if that helps improve grip levels.

Much of what we’re discussing is about driving on level hollowed-out or boulder-strewn tracks, or hill-climb tracks. Don’t forget that you can often easily descend a rocky track in a 4WD that won’t be a piece of cake to climb back up again.

Make sure that you have an alternative track to get back out, or avoid the track altogether if it is truly a gnarly climb out. There is no dishonour in avoiding a difficult track where you can.

You will also soon find you can’t pick your way on a difficult track well from the driver’s seat – there is too much you simply can’t see. Get out and have a proper look at difficult sections and, if necessary, have a guide help you with picking a line with voice and hand signals (or use UHF radios).

This will help your tyres get the best grip and avoid deep hollows or the underbody hitting damaging rocks.

Make sure that your watcher/s stay well clear of the vehicle though, in case for example it unexpectedly bounces off a rock.

Driving on rocky trails – Quick reference do’s and don’ts

• Do get some 4WD training before tackling rocky tracks
• Do prep your 4WD, if you can, with a lift kit, off-road tyres and diff locks
• Do take recovery gear such as a winch, bottle jack or high-lift jack
• Do take off vulnerable parts like side steps and tow hitch
• Do approach rocky tracks in the lowest gear possible with all traction aids on
• Do get a spotter to guide you on tight tracks

• Don’t run standard highway tyre pressures – drop them
• Don’t push hard on the accelerator and suddenly back off; this can do drivetrain damage
• Don’t allow wheelspin when slide-sloping in steep terrain or you might slide off the track
• Don’t get under any vehicle that is in any risk of slipping
• Don’t head down a track you know you can’t get back up unless you have another route

Related:
How not to get lost in the bush
Top-10 4WD rookie mistakes
Guide to 4WD off-road tyres