Safe Driving on Corrugated and Washboard Roads
With South Africa having the 10th largest road network in the world, and about 600,000 km of unpaved and gravel roads, road users can expect to find many different road conditions.
Some of these gravel roads might not be smooth - these roads are known as corrugated or washboard roads.
On the Arrive Alive website, we find a rather comprehensive section about safe driving on gravel roads. But how do the corrugation of gravel roads affect our driving style and how should we adjust our driving for safely?
We approached the experts from MasterDrive to gain some insights!
What is Corrugation or Washboarding of Roads?
Corrugations are formed through material displacement as a result of tyre action coupled with the mass and speed of the vehicle. The surface material arranges itself into parallel ridges which lie at right angles to the direction of traffic.
Spacing (wavelength) can vary from 500 mm to 1 m and depths can range up to 150 mm. Any irregularity in the surface can start the process which then develops at a rate dependent upon the traffic, speed and tyre pressure.
Granular materials with particle size greater than 5 mm, low plasticity and limited fines, or which have lost fines due to traffic action, are susceptible to corrugations. In dry climates, only the material that forms the ridges is affected with the underlying material remaining in place.
Maintenance or corrective action consists of respreading the materials and cutting to the depth of the corrugation.
In wet climates, the development of corrugations and remedial action depends on the season. In the dry season, corrugations develop similarly to that in dry climates with the same remedial action necessary to correct the defect.
However, in the wet season surface deformations may be transmitted into subgrades and lower pavement layers by water penetrating the surface, causing structural defects. Deformations in subgrades and lower pavement layers may, as a result, be in or out of phase with the corrugation. Where the deformation and corrugation are out of phase, weak spots may appear as potholes at the trough of the corrugation.
The absence of a tight surface, combined with coarse sandy material, if present in high proportions, can lead to the rapid formation of corrugations.
Why do dirt roads corrugate?
Washboarding or corrugation of roads comprises a series of ripples, which occur with the passage of wheels rolling over unpaved roads at speeds sufficient to cause bouncing off the wheel on the initially unrippled surface and take on the appearance of a laundry washboard.
Is it better to drive fast or slow on a dirt road?
Less speed is better. Do assume that any and all animals that you encounter on any road will instinctively head towards you. Drive past them slowly. Do slow down for oncoming vehicles and move to the left as far as it is safe to do so
Is driving on dirt roads bad for your car?
Remember, travelling on dirt roads can have a negative impact on your vehicle. After your drive, make sure you clean the outside of your car immediately as mud and dirt can cause rusting if it's left unattended long enough.
How do you drive on corrugated roads?
Pick your Line
While you are obliged to follow relevant road rules it is not always necessary to 'stick to the left' if it means you must drive on the worst sections of the road. Pick the smoothest line and anticipate badly corrugated sections by the changes in the road.
Tips for Driving on Corrugated and Gravel Roads
One of the realities of life on the road is that not all roads are created equal. Judging what roads to travel down and if your vehicle and driving skills are up for the challenge of that particular road will be a daily decision for motorhome owners.
Let us be clear from the outset, Motorhomes and Campervans are not designed to be driven on corrugated roads for significant periods of time. There is simply too much furniture and too many appliances hanging off walls and that will be literally rattled lose under sustained corrugated road driving.
There are exceptions to this. Some specialist manufacturers build a purpose-designed off-road 4WD RV. The rigidity and compactness of these vehicles come at a cost. If driving serious bush tracks in a motorhome or campervan were something you wanted to do, we would recommend that you purchase a vehicle built for this very specific style of touring.
However, it is likely that at some time on your travels you will be faced with a few kilometres of dirt road between you and the perfect free camp, amazing view, or even a very special Shiraz producing vineyard!
How do you safely navigate dirt roads in a Motorhome?
Anyone who has lived in a rural community and has had to deal with regular driving on dirt corrugated dirt roads will be able to tell you that there as many opinions as there are experts at the pub! The purpose of this article is to clarify a few facts, perhaps blow up a few myths and manage expectations about what a motorhome “should” be able to handle.
This is a matter of personal choice, certainly, lower pressure makes the ride smoother but it also increases the tyre temperature and potential for damage to the tyre and a blowout. Ambient temperature also needs to be factored into the equation; hotter days increase tyre temperature. In short, lower your tyre pressure when hitting the dirt and test out what feels right for your particular set up.
Pick your Line
Corrugations are worst where people brake or accelerate. For instance: the entry and exit of corners or the crests of hills. Dirt roads often run through wide-open expanses where visibility extends for kilometres and on-coming traffic can be seen well in advance.
While you are obliged to follow relevant road rules it is not always necessary to 'stick to the left' if it means you must drive on the worst sections of the road. Pick the smoothest line and anticipate badly corrugated sections by the changes in the road. By anticipating the changing conditions, you will slow down naturally where required, without breaking, and create a smoother ride.
What About Suspension?
When travelling on corrugated surfaces your vehicle’s suspension system is having a pretty stressful time. Your shock absorbers, in particular, work hard over corrugations and heat up. In these conditions, it is best to take regular breaks and let them cool off.
Also, keep an eye on your shock absorber bushes as they can easily be chewed up on corrugations.
Some dirt road cattle grids are pretty rough, and if hit at a speed they can buckle rims or put out your wheel alignment. Try to travel at a speed that will allow you to slow down for them.
Pack it Tight
It is difficult to describe how much rattling and moving will occur inside cupboards, draws and lockers of a motorhome. Every plate, glass, can or bottle needs to be wrapped and secured
The biggest deterrent for driving corrugations in a motorhome will be the noise. No matter how well you pack, the rattles, bangs and crashes will make for a very loud and disturbing experience.
We’ll go through some tips which will help you get to your destination safely.
10 Useful Tips for Driving on Dirt Roads
1. Slow Down
The number one rule when driving on dirt roads is to slow down.
Why? Because you can’t stop as quickly on dirt as you can on tar. Plus, there are heaps of hazards you simply don’t encounter on tar roads. Things like washouts (big gutters across the road caused by rain), rapidly changing road surfaces, dust, large rocks and everyone’s favourite, corrugations!
Dirt roads can throw out all sorts of challenges. Stay alert and concentrate on the road ahead.
And you’re more likely to encounter wildlife, cattle, sheep, pigs, goats, wedge-tail eagles and so on. You really don’t want to hit a cow at 100km/h.
Why else should you slow down? To protect your vehicle and its tyres. You might not notice in your comfortable cab, but your vehicle takes a pounding on dirt roads. The faster you go, the more likely you’ll damage something or puncture a tyre.
2. Drive to Conditions
Yes, I know. You’ve heard this a million times before and it has kind of lost its meaning by now.
A typical dirt road… rocks, soft surface and corrugations.
However, it’s true… and applies ten-fold on gravel roads. If the road’s rough, slow down. Yes, the 4WD ads might show your beast climbing over mountains of rock and conquering Mt Everest (okay, that’s a slight exaggeration). The truth is very different.
Any road-registered vehicle hates two things. Continual vibrations like corrugations, plus large impacts like hitting a washout at high speed tend to break, bend, loosen and snap components. And you guessed it… the faster you go, the worse the effects.
The second thing a road-registered vehicle hates is becoming airborne. Well, not so much becoming airborne… more the crash-landing at the end. You can do massive damage if you jump a vehicle that’s not designed to jump. Bent suspension components, body or even chassis damage are all possible.
So that’s why we say drive to the conditions. If the road’s rough or has lots of dips, take it easy. It might take a bit longer, but at least you’ll get there.
3. Slow Down for On-Coming Traffic
When you’re on the dirt, think of other road users. Slow down for oncoming traffic. This way you’re much less likely to throw up a rock into their windscreen. Hopefully, they’ll do the same thing.
Follow a simple rule… the bigger vehicle has right of way. If a bigger vehicle is coming your way, be prepared to slow right down or pull off the road and stop. The bigger the vehicle, the harder it is for them to slow down quickly on dirt.
Not only this, on a rough road surface it’s really difficult for a larger vehicle like a truck to pick up speed again. They tend to bounce and buck over the rough stuff, which really isn’t too comfortable!
Give trucks plenty of space. It’s impossible for them to pick up speed on a surface like this, once they’ve slowed down.
So be considerate and thoughtful of other drivers.
4. Pay Attention to Tyre Pressures
If you’re driving on dirt roads, lower your tyre pressures. As a really rough guide, if you normally run 40psi in your 4WD then try 28-30psi on dirt. This allows the tyres to absorb some of the harshness coming back from the road. Plus, it allows them to flex around rocks and sticks, meaning a puncture is less likely.
We always drop the tyre pressures on our truck when we’re off the tar.
So, you’ll get a smoother ride, won’t damage the vehicle as much and are less likely to get a puncture.
Millions of words have been written about tyre pressures. Just keep it simple. As I said, 28-30psi is generally a good starting point. You might need to go lower if the road if really rough and slow or you’re in sand or mud.
If you’re running a light truck, you’ll need to experiment a bit based on the weight you’re carrying, type of tyres and so on.
5. Find The “Right” Speed on Corrugations
If you don’t know how to handle corrugations, you’ll likely be in for a teeth-chattering ride. Go too slow and you’ll feel every single corrugation. Go too fast and you’ll probably make an unplanned detour into the scrub!
There’s a happy medium.
Build up speed until you feel the corrugations smooth out. This usually happens around 50 to 60km/h depending on the type of vehicle, how big your tyres are and how big the corrugations are.
It’s easy for your speed to creep up. Keep an eye on your speed and only drive as fast as necessary to smooth out the corrugations.
One of the least comfortable experiences is corrugations on corners. You often have to slow down for a corner, only to be pounded to pieces. There’s not much you can do about this.
Far better to put up with the rough ride, than to meet an oncoming vehicle when you’re halfway around a blind corner on the wrong side of the road.
And sometimes you simply can’t avoid being shaken to pieces. You might be on a badly corrugated winding track, where a reasonable speed is out of the question. In these circumstances slow right down and put up with the punishment.
A winding, sandy corrugated road like this makes getting up to a comfortable speed almost impossible. Sometimes you just have to slow right down.
6. Drive Smoothly
What do you do when you’re walking across a slippery, wet floor? Do you run and make sudden changes of direction? Or do you walk and make sure every movement is smooth and fluid? I’m guessing the latter unless you like slipping over!
Do the same on dirt roads. They’re way less grippy than tar roads.
Slow down and drive smoothly. It’s simple as that. No sudden changes of direction, no standing on the brakes and no foot-to-the-floor acceleration.
Smooth, smooth, smooth. That’s all you need to remember.
And if an animal launches itself into your path, don’t swerve whatever you do. You’re far better hitting the animal than swerving wildly. Neither option is good, but a swerve is far more likely to get you into big trouble… like ending up on your roof in the scrub.
7. Read the Road Ahead
On tar roads, we become complacent. We tend to sit back and steer, take in the scenery and generally cruise along with not a care in the world.
You can’t do this on dirt roads. Concentrate, look ahead and read the road.
What do I mean by “read the road”? Look beyond your bonnet, see what’s coming up in the distance. Look for changing road surfaces like potholes, dips, rough or rocky patches, mud, wildlife and so on.
An example of rapidly changing road conditions. These bulldust holes appeared out of nowhere on an otherwise good road. You never know what the fine powdery dust is hiding… often big rocks or huge holes.
By looking ahead, you can prepare early. You have a chance to slow down before you hit a rough patch. And don’t race up to the rough patch then brake hard. Anticipate. Start slowing down early, by backing off the accelerator and letting your vehicle wash off speed.
Then when the rough part is behind you, accelerate slowly and smoothly. If you stand on the accelerator, you’ll simply bounce your driving wheels on the rough stuff. Not only does this make for a rough ride, you’re also damaging the road for the next person.
8. Avoid the Dangers of Dust
Dust goes hand in hand with dirt road driving. It can blind your vision. There are 3 really important things you need to know.
Following Another Vehicle
If you come up behind another vehicle, stay out of their dust. Turn your headlights on soon-coming vehicles can see you.
Whatever you do, don’t overtake blindly through a cloud of dust. It’s incredibly dangerous and has been the cause of many head-on collisions over the years.
Passing an On-Coming Vehicle
When you see an oncoming vehicle, slow down and be prepared to stop. If their dust is blowing across your side of the road, you’ll probably need to stop. Again, headlights on and take care.
Vision obscured by an oncoming vehicle. Slow right down or stop, and make sure your headlights are on. You never know what might be hiding in that dust.
Being Passed by Another Vehicle
Always check your mirrors regularly for approaching vehicles. A little consideration goes a long way in the bush.
9. Learn to Dodge Rocks
Dirt roads and rocks go hand in hand. If you’re on dirt, you’ll most likely encounter rocks. They vary from razor-sharp splinters as long as your finger to great lumps of rock as big as your head, depending on the terrain.
Don’t drive over them. Of course, if the road is covered in rocks, you’ll have to drive over some of them. But slow down and avoid the worst ones.
Your 4WD is not an indestructible dirt road-conquering weapon, despite what the manufacturers’ marketing departments would have you believe. Tyres hate rocks… rock love tyres.
This is typical of the country where you’ll most likely encounter tyre-shredding rocks.
Not only tyres either. Rocks can do a whole lot of damage to the underside of your vehicle.
Slow down, avoid the worst rocks… and understand your vehicle is not indestructible.
10. When Not to Drive
Avoid dawn, dusk and at night. This is when wildlife is most active and you’ll increase the chances of a collision.
Your vehicle might have a bulbar, but that’s no guarantee your vehicle won’t be damaged. animals have a nasty habit of hopping straight into the side of your car, which is a bit disconcerting! And remember that an animal can do a whole lot of damage if they go under your vehicle.
If you have to drive at night, dawn or dusk then slow down. A quality set of driving lights is a priceless addition in these conditions. Keep a close eye on both sides of the road and if you have a passenger, get them to help you spot wildlife.
Driving safely on dirt roads is a skill you can learn. If you only take one thing from this article, it’s this… slow down! Slow down, look ahead and drive smoothly.
Some of the most incredible places in South Africa can only be found along dirt roads. Learning this skill will allow you to enjoy all our sensational country has to offer
[A word of Appreciation to MasterDrive for the assistance received]