By Robert Pepper via practicalmotoring.com.au
Driving across a hump should be one of the most basic off-road skills in a four-wheel driver’s arsenal. It’s a bit trickier in an SUV, but not impossible. Here’s how to tackle a hump in an SUV.
YOU FIND HUMPS in many places; sand dunes, rocks, forests, track exits or entrances. Perhaps the most common are the artificial ones on hilly 4WD tracks, put in place to drain water away so erosion is reduced. Being a 4WD track, this work is usually just a rough and ready pile of dirt, not a finely engineered culvert with a gentle approach.
Driving over a hump is easy enough in many 4x4s. The approach is typically gentle enough so the front of the car doesn't hit the earth, but the problems, if any, tend to come as the vehicle goes over the top. It's surprisingly easy to end up with the 4WD balanced on its belly, all four wheels either off the ground or close to it.
In that case, you have a recovery on your hands, which is quick and simple if you have a snatch strap and another car. Or a winch with a handy tree as an anchor. If you have neither, then it's going to be a long afternoon with jacks and a shovel.
But you don't want the ignominy of a belly-out, you want to do it properly. Here's how:
First, approach the obstacle slowly, and ease over the top. You'll probably use second- or third-gear low-range, or in cars without low range, first gear. A lower gear is better as it allows smoother control and engine braking over the top.
As ever with off-roading, kill the radio so you can listen to the car. You're trying to hear if the car's belly touches as you crest the hump. If it does, don't worry because a light touch won't be a problem. But if it does touch, then you have a choice.
You can either back up and try again with more momentum. This could see you sailing over the top quite nicely with just an underside scrape which won't worry any 4X4, or it could see you bellied out, all four wheels dangling, going nowhere. Before you try this, get out and look at where you are. If the car has bellied out anywhere before it's level, the momentum approach is going to be even riskier than usual.
Or, if the car touches, you could back right off and try a different way.
Approach the hump, but to one side of the track. As you start to climb the hump, angle the car as far you can relative to the track, and ensure that if there are any ruts, your wheels aren't in them. By angling off like this, you improve what's known as the 'ramp angle', which is how steep and sharp a hump the vehicle can drive over.
There's a disadvantage to angling off, and it's apparent in the profile photo shown. See how the front right wheel has dropped down, and the rear right is tucked up under the body. Going diagonally over a hump does that, and the risk is that the front right and rear left wheels will spin because they have little weight on them.
The solution is judicious use of momentum, or traction aids such as electronic traction control or cross-axle differential locks.
A final option is track building, maybe putting a rock or two under the wheels to effectively flatten out the hump.
Whichever way you choose, as you clear the hump you need to think ahead and consider the next part of the track. The tip here is as the rear of the car descends the downhill of the hump, use that gradient to accelerate so there's enough momentum to conquer the following ascent.
One thing to remember about soft roaders is that while they can often make their way along rough tracks, it takes more time, skill and care than a larger vehicle with low range. This is fine if you don't mind, but it is one reason why if you want to go touring in the bush, then a low-range vehicle is what you need.