How road corrugations form

Submitted: Friday, Jul 06, 2012 at 18:05
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Found this interesting article by Dr Karl on how road corrugations form ...

http://www.abc.net.au/science/k2/trek/4wd/Overcor2.htm
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Reply By: Sigmund - Friday, Jul 06, 2012 at 18:19

Friday, Jul 06, 2012 at 18:19
Good read. Thanks for posting.

Some experts say that the shape of the corrugations is asymmetrical and you get a smoother ride if you travel on the wrong side of the road.
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Follow Up By: rocco2010 - Friday, Jul 06, 2012 at 18:46

Friday, Jul 06, 2012 at 18:46
Gidday

Do these experts drive over the same section of road twice to test the theory? Gluttons for punishment they must be.

cheers

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Follow Up By: Motherhen - Friday, Jul 06, 2012 at 23:48

Friday, Jul 06, 2012 at 23:48
Hi Rocco

LOL - sometime we have to travel the second time to get back home again.

When we went to Mitchell Falls from the King Edward River camp ground, the road was pretty bad. On they way back, it was a lot quicker and smoother. Everyone in camp commented. The corrugations formed on the uphill run, and were much easier on the down hill run.

My home access road gets bad which ever side we drive on - it doesn't take long before it is all as bad with no way to dodge the corrugations. The worst is on the uphill slopes at either end of the road.

If the underlying corrugations are not graded completely smooth, they bounce back very soon. This is evident on roads such as the Great Central or Gibb River. A week after grading they can be just as bad with the amount of traffic and the speed so many travel at on them. The base corrugations can still be seen even if you follow the grader.

Motherhen
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Follow Up By: rocco2010 - Saturday, Jul 07, 2012 at 00:17

Saturday, Jul 07, 2012 at 00:17
Hello Motherhen

Can I start by saying I enjoy your contributions here .. you are certainly well travelled and very wise.

I was out on the Gunbarrell last year and there was a retired wheat farmer in the party and he said he never had any trouble with corros on the farm tracks until his son learnt to drive ... it is all about speed, he said.

As for the uphill downhill thing ... on the Canning a few years ago we camped a couple of nights at well 34 which is a few ks off the main track. We were doing some work there which involved travelling back and forth a couple of times and it was noted that where the access track crossed one of the low dunes in the area it invariably had a turn at the base and for the short distance either side of the dune the corros were much less severe, presumably because that was where people had to slow down for the turn and then go up the dune and then go slow down the other side to the turn. Maybe you need to slow down on the way to the gate ...

Cheers




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Follow Up By: Motherhen - Saturday, Jul 07, 2012 at 13:23

Saturday, Jul 07, 2012 at 13:23
Hi Rocco and thanks :)

Speed certainly makes a difference. We had four children - all needing vehicles to go in different directions to Uni, TAFE or work. Add to that their mates visiting on weekends. They sure knew how to corrugate the track quickly :O

There is a lot more bounce when driving on the uphill slopes than on the flat. Sometimes we have been touring and people have said "I wouldn't have taken a caravan on xxx road" and i have said "The worst corrugations were on our access track coming home."

Mh

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Reply By: Les - PK Ranger - Friday, Jul 06, 2012 at 18:38

Friday, Jul 06, 2012 at 18:38
Yep, there is usually (but not always) better driving on the opposite side of a corrugated road, but that is fraught with obvious danger : )

There is the urban (or is that rural) legend of the 4wd travelling at speed on the opposite side of a badly corrugated road, and the driver stays on the right hand side as he crests a small hill.
As he crests, he nearly soiled himself as he sees another 4wd travelling in the opposite direction, also on the wrong side of the road !
Their eyes meet and the look of terror / relief in their eyes says it all.

If either had been on the correct side of the road, there would have been a bad accident, and by blind luck they had both been using the reduced corrugations to advantage.

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Follow Up By: Member - Rod N (QLD) - Friday, Jul 06, 2012 at 18:52

Friday, Jul 06, 2012 at 18:52
Back before bitumen roads Granddad and Dad always drove on the wrong side of the road when possible. If this happens a lot wouldn't the "good" corrugations eventually change sides?
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Follow Up By: Holden4th - Friday, Jul 06, 2012 at 20:42

Friday, Jul 06, 2012 at 20:42
Have you noticed that the corrugations are always worst on corners?
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Follow Up By: Sigmund - Saturday, Jul 07, 2012 at 07:58

Saturday, Jul 07, 2012 at 07:58
Corners with a slope, yes.
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Reply By: Member - blackbird1937 - Friday, Jul 06, 2012 at 22:10

Friday, Jul 06, 2012 at 22:10
Thanks Sonshine , that is very similar to a report I read quite some years ago on what caused corrugations . I can show you about 100 metres of corrugated asphalt road on the Hume Freeway near Wandong Vic. I can remember most people driving on the right hand side of the roads to smooth the bumps out and did it myself for years and still do it if the road is bad enough and there is not much traffic around . In the early 50s my fathers friend told me there is only 1 way to smooth the corrugations out and that was to put your foot down like he did . No one ever went to the correct side of the road to pass but carried on their merry way . Many times the plain dirt roads were better and smoother to drive on than the gravel roads . The corrugated gravel roads in the back blocks are no worse today than the Vic roads were in the 40s and 50s .
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Reply By: Member - Sonshine - Friday, Jul 06, 2012 at 22:25

Friday, Jul 06, 2012 at 22:25
The dreaded corrugations had a win over me a few days ago.

We were headed south out of Kakadu along the Kakadu Highway towing our A'Van which are not known for their offroad abilities. Still, we thought we would test the boundaries and turned East up the track to Gunlom.

The corros were pretty bad, but with low tire pressures and maintaining a skimming speed of about 70 kph, we were tripping along nicely...

...that is until the straps holding the water tank under the A'Van decided to let go, and the water tank "left the building".

Corrugations 1, A'Van 0

Boundaries tested.

Gaz
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Follow Up By: PeteS - Saturday, Jul 07, 2012 at 09:00

Saturday, Jul 07, 2012 at 09:00
Sorry to read about the water tank departure Gaz. I hope its repairable.

The comfort speed over corrugations in your tow vehicle can be very different to that of your trailer/camper/caravan as each has a different suspensions set up. I would love to know of a 'safe' method to find the best speed for both the car and van on corrugated roads.

There has been times when the speed to get above the corrugations was too fast for me to feel safe.

I'm happy to see you appreciate that tyre pressure make a huge difference to assisting the suspension. Just remember the speed is proportional to pressure i.e. the lower the pressure the lower the speed travelled.

Cheers,
PeteS
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Follow Up By: Member - Sonshine - Saturday, Jul 07, 2012 at 09:14

Saturday, Jul 07, 2012 at 09:14
Thanks Pete - its all a learning experience :)
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Follow Up By: rooster350 - Saturday, Jul 07, 2012 at 10:55

Saturday, Jul 07, 2012 at 10:55
The water tank of our Avan is in the van...back left side corner, but ours is a dual axle poptop Avan....it is not an off road van by any means but it sure has been over some VERY rough roads without any structural mishaps...cheers
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Follow Up By: Sigmund - Saturday, Jul 07, 2012 at 13:41

Saturday, Jul 07, 2012 at 13:41
Despite all the spec checking and prep, I've found the bottom line is suck it and see.

And have progressively ramped up the challenges over 3 annual trips.

We've just spent 3 weeks in the Channel country with the Forester and a Johnno's 'light off-road' CT. Did two long roads rated temporarily as 4WD, but found that just meant track width and rut depth, and the rig is on a par with 'real' 4bies on those dimensions.

We even easily did Little Red outside of Birdsville, while other day-trippers in big 4bies stayed at the bottom, reluctant to try their hand.

Forester prep for me is a proper sump guard and LT AT tyres. And compressor.

Things rattle apart; mostly 12v lights and connectors. Have learned to carry and use spares.

Part of the price. Just love being outback.
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Follow Up By: PeteS - Saturday, Jul 07, 2012 at 15:05

Saturday, Jul 07, 2012 at 15:05
.... Things rattle apart...............
I have to agree with you there Sigmund.

Every time you stop, get out and check around and under the vehicle. Amazing what I find working its way loose when I'm having a cuppa at a roadside stop or filling up with diesel at the servo.

Often pays to get under the van and tow vehicle to check things at the end of the day or before you head off each day.

Saves a lot of missing nuts, bolts and expensive damage and missing equipment.

Cheers
PeteS
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