4x44X4 AdviceCar Advice

How to drive over a hump off-road

Driving over a hump is one of the most basic off-road skills, but it’s a bit harder with a road-oriented 4×4.

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 minimised.  Being a 4WD track, this work is 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 4WDs.  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 a 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 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 offroading, 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’s any ruts your wheels aren’t in them.  By angling off this you improve what’s known as the ‘ramp angle’, which is how steep and sharp a hump the vehicle can drive over. Like so:
 

IMG_5112
Those puddles are only a few centimeters deep, but if the Santa Fe had been drive straight over the top it would have been bogged. The puddles are invisible from the other side of the hump, so the only way to know is to get out and check.

 

IMG_5110
Doesn’t take much to get a softroader close to being bellied out. The car is angled off – check the relative positions of the front and rear wheels to the body.

In the photos above the Santa Fe’s belly initially touched the top of the hump when driven straight over, and had I continued the front wheels would have dropped into those deepish puddles which would have worsened the problem by increasing the effective size of the hump, and reducing traction thanks to the water.  The angling off provided just enough improvement in effective ramp angle to clear the hump, and it avoided the puddles with their holes.
 
There’s a disadvantage to angling off, and it’s apparent in the second photo.  See how the  front right wheel has dropped down, and the rear right is tucked up into 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.  In this case, the climb wasn’t steep, but it was slippery, especially on those road tyres.
 
How did I know to do this?  Experience is all.  I know that softroaders like the Santa Fe have limited clearance, and the hump looked large so I took it easy.  The car scraped, I stopped,  hopped out, assessed the situation and tried again, this time angling off.  Took a couple of photos, hopped back in and off we went.
 
Had I been driving a larger 4WD with better clearance, say my own Ford Ranger which has better clearance out of the box (and then I’ve lifted it further), then I would not even have hesitated as there’s very few humps that cause such vehicles any problems.  But one thing about softroaders is that while they can often make their way along 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 4WD touring then a low-range vehicle is what you need.
 
 


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Robert Pepper

Robert Pepper