Trail Savvy: Rock Crawling

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Although not always ideal if you want to avoid vehicle damage, rock crawling is sometimes a necessity. South Africa, in particular, is a very rocky place − and if you’re going to drive off-road, you’ll come across rocky terrain sooner rather than later.

The word ‘crawling’ in ‘rock crawling’ explains everything, and means that you’ll be going extremely slowly in first-gear low-range and climbing over large, often loose boulders which may be a challenge… especially in a standard 4×4.

Preparing your vehicle

Depending on the terrain, it’s often necessary to deflate your tyres. In rock, whether it is loose or firm, you’ll need to deflate the tyres for extra traction. A rough guide of pressure is that 30% lower than standard road pressure is advised, although you will be able to drop your pressures much more if you have high ground-clearance. Dropping the tyre pressures extends the footprint of your tyre and allows the rubber to mould itself around stones, as opposed to driving on top of them.

Dropping pressures will also reduce wheel spin, helping to conserve the track, but it will lower your ride height, too. If you have a standard vehicle with side steps, remove the steps entirely, otherwise you will almost guarantee a few dents. Speaking of dents, make sure that your vehicle has sturdy underbody protection; the standard engine/gearbox/transfer-case protection on most modern 4x4s is very flimsy. Differential casings are tough, but are also exposed to knocks.

With any standard vehicle doing frequent rock crawling, it is highly recommended that you have aftermarket protection like bash plates, rock sliders, and heavy-duty bumpers, and that you remove your tow bar.

Diff-lock vs traction control

When the Discovery 3 was released, Land Rover’s Terrain Response system set the benchmark for all 4×4 traction control systems. Since then, most high-end 4x4s have been equipped with sophisticated traction-control systems that improve with every new model. That said, there are situations in which a manual locking diff works best − typically on only the rear axle, but on hardcore offroaders, on the front as well). In loose, rocky terrain, the reactive response of a traction control system, though fast, will often spin a wheel before locking up, and then frustratingly let go again before you have properly cleared a section, allowing the vehicle to lose momentum before launching it forward again.

Newer systems in those high-end SUVs are getting better; but, for the most part, engaging the diff-lock before a technical section will reduce wheelspin and maintain momentum until you are on easy ground.

Road building and inspection

Before a technical section, walk your route and plan the exact trajectory of your tyres, keeping in mind your available clearance and the likely traction available for the tyres. Stay on top of rocks, and look for a clear passage for the lowest points – usually the differential centre. That quick stroll may save you expensive damage, or at least an embarrassing tow.

If you notice deep cross-axle ruts and loose stone, pack the ruts with rocks; and if you have them available, lay MaxTrax recovery tracks on top. Try to keep things level and avoid fully extending your suspension travel, as less weight on the wheel means diminished traction. This is especially important on the front end, where diff-lock is not available on most vehicles.

DISCLAIMER

This information is offered in good faith, and is intended as a guideline only. SA4x4 accepts no liability. Use common sense, and engage your brain before touching the gear lever.

Slow and steady

Momentum is often confused with speed, but bear in mind that speed + rocks = vehicle damage. That said, stopping on a steep and rocky incline may get you stuck, so try to plan out your line beforehand and stick to it, maintaining momentum in your vehicle’s power band. This is often difficult in a manual 4×4, but is certainly worth practising. Most rocky climbs will require first-gear low-range, as will the descents. Using your Hill Descent Control on the way down may seem like a good idea, but nine out of ten systems are complete rubbish − and all of them can only react to an increase in wheel speed, which is almost always too late… with the exception of certain vehicles equipped with crawl control. In general, on steep rocky descents, keep your vehicle in first gear (lock it in manual mode with an auto gearbox, which has less downhill braking ability) and hover your foot over the brake so that you can pre-empt drop-offs and roll off them in a slow, controlled manner.

Andrew Middleton is obsessed with anything wheeled, and has been in and around 4x4s since before he could talk. He lived out of a Land Rover in Central America for eight months, and has been stuck − usually not for long − in every sort of terrain from the Okavango Delta to the Namib Desert. andrew@sa4x4.co.za

By Andrew Middleton

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