Driving on Corrugations

Hi Wayne

No doubt this will bring out as many views as there are corrugations on the CSR.

My take on it is that you are better slowing down, rather than going fast with the objective of skipping over the top.

My reasoning is born from a view that things break when put under stress (G-forces) and therefore the faster the speed over the 'bumps' the greater the G-forces you are applying to components on a vehicle - at some point they will break when exposed to opposing forces.

Aircraft apply the same principal, when flying in turbulence they actually slow the aircraft down when going through the 'bumps' as there are components in the aircraft that will break beyond a certain 'G-rating'.

The same applies for a boat going through choppy conditions.

Logically this thoery applies to vehicles. Whilst not having the same off-road exposure as yourself, I have always slowed down when on corrugations and I am yet to break anything.........

Regards
Baz

Ahhh Wayne

Is there definitve answer???...LOL.

We are going to see some interesting replies.

I would think that I have minimised damage by running tyre pressures on truck at 20psi and on trailer at 10psi and trying to maintain a speed of 60kmh on the Anne Beadell and some other corrugated tracks. Others say 80kmh is better so that the vehicle gets up on a plane ( like a speedboat ). This is not always possible.

On the Gunbarrel I sat on 80kmh and some parts of the old Tojo came loose and fell off...lol.

Coil springs seem to work better for me and my OME shocks on the GQ did not get too hot.

Cheers

Corros. Ug ! I hate em with a passion. But there are corros and there are corros. Those on the Cape can rival those on the Gunbarrel, and there's every variation in between to be found. Regardless of where they are found, they're not good.
Some travel as fast as they can over them. These people often seem to come to strife. I've found that the old 80km rule works for me. One of the problems is getting going again when you're stopped. Everything shakes. Heavens only knows how the ladies survive such a shaking.
Good suspension such as OME improves the ride dramatically. Springs are more comfortable than coils.
There is only one good thing to be said about corros : when you eventually get to the end of them, you can finally unglue your top teeth from your bottom.

All I can say is that to go slow over them means a very long trip.

At 60-80kph, or whatever, there seems to me to be less stress on everything.

Getting started, at first, is OK as the vehicle goes up and down the corrugations. Then as the speed increases the shaking really concerns me, until the point is reached where you're 'skipping' over the top of them and the vibrations seem to be less severe.

At the Cape I tried the slow method for a while but gave up just so I could reach the destination before old age set in.

Luckily the Troopy didn't rattle to pieces, nor did the teeth drop out, but what a noise!

Couldn't you make your unsuspecting customers guinea pigs by trying various methods and give us all the answer?

Banjo (WA)

Wayne, I tackle corrugations with low tyre pressures as Willem stated and lower speeds. Even 40k's/hr if need be.
I was terrified on a Cape trip a few tears ago when coming down the Development Rd when the high speed theory travellers come screaming around a corner in a side drift because they have lost most of there traction.
The slower speeds usually don't worry me cos at some stage in the trip, you will pass the speeders while they are repairing shockers or getting bits and pieces replaced or repairs to their vehicles.
I figure it is better to preserve your vehicle than have to pay dearly for repairs whilst on the road.
That's my 22c worth (GST Included)

Without a doubt, you need to drop tyre pressures. Common sense tells me that more shock that is aborbed though the tyres means less shock through everying above them.

The 70/80 KPH rule has woked for me for a lot of the roads BUT not all. Tyre pressure adjustment has also helped. The other thing that has worked for me has been driving on the other side of the road as it seems that the shape of the corrugations are slightly sharper on the correct side of the road. Yes I make sure I'm not there around some bend etc.

Kind regards

To me decreasing tyre pressure is the most important thing. Not so much that your tyres are going to overheat, but enough to carry your load but soften the blow.

Other than that, it is important to watch the temps of your shocks - put your hands on them at each stop and get to know how they perform. Same for the temps on your tyres. If either are getting real hot - take it a bit easier.

Dead slow may work, but there is some sort of balance with practicality here.'

On the A-B (Coober Pedy side) and a couple of other Nullabor roads (Israelite Bay Balladonia for instance) this year was the worst I have encountered for some time, and I got home with everything intact except one roof rack bracket - but tyres were new (ran 23 Fr 27 Rr - STTs and 20 on the trailer STs) as were shockers and coils.

Well actually, I did have a trailer problem, but this was due to poor tensioning on the suspension nuts due to broken torque wrench damn it (trailer guy's - not mine).

One of my customers limped home with a crook shocker - perhaps two, and another with a crack in his barn door - GU Patrol.

We were generally doing 60-80 ks on dirt roads.

Ciao for now
Andrew.

Which part to you want to break first?

Higher speed lets the cabin of the vehicle 'float' and gives you a good ride but the suspension will take a hammering. You may be sitting in comfort but the suspension is doing its job and absorbing all the bumps and bangs.

Slower speed is not as comfortable and some of the vibrations are transmitted into the cabin.

Take your pick. If it's a hire or mine vehicle..........

Wayne
I have been pokin about on Corrugations since 1966 and find that it depends on what your driving, I was driving a T-Line International Road Train Car Carrier 1980-82 Brisbane to Darwin , on the 88klm of dirt that was there between Winton and Boulia [sealed now] it took 6 hours just crawling along but if I seen a few hundred meters of smoother stuff then I would just pop it up a gear or two ,so I apply the same theory to my 4x4 ,if the corrugation is small I can get up on top and cruise at 100 with caution but if it is bad stuff then I don't care if I drive all day in second gear, so just feel it out and drive to the conditions and have patience , OMEs help too .

Doug

I don't think there is a fixed rule other than, drive slower, with lower tyre pressures. Type of vehicle, it's condition, weight, suspension, driver experience and type of corrugations are all factors.

On our recent trip which included GRR, Kalumburu Road, Mitchell Plateau Track, Cape Leveque Road, Bungle Bungles Road and others, we had plenty of opportunity to experiment.

As a general rule I dropped all tyre pressures by 10 to 12 lb. Most commonly we ran at 25 to 28 front and CT and 30 to 34 rear. Generally the right speed was around 75 KPH, sometimes a touch more, sometimes a bit slower.

But there were some areas where the only answer was to slow to 20KPH and ride over every corrugation. This is on the 'super corrugations' which seem to be a foot deep and a foot or more apart.

We normally stop for a short break or driver change at least every 2 hours. We do it a bit more often on the bad roads. We only noticed bad shocky fade once which was solved by a short break.

Apart from UHF antenna top breaking off and a couple of screws working loose, we had no damage. Came across others with blown tyres, broken springs and shocks, broken and lost wheel studs, wheels come off and lots more.

Some of these had never heard of adjusting tyre pressure and one insisted he had lots of experience and he always goes up to 50 PSI on corrugations.

Medium to large corrugations…25 psi @ 75 kph
Huge corrugations……..25 psi @ 30 kph
These speeds smooth the bumps out enough to make the ride bearable while still having reasonable control to avoid potholes, dips & washaways. Any faster & one risks the car floating with little chance of avoiding obstacles. 25 psi allows the tyres to mound around the bumps without compromising too much on road handling or causing tyre damage.
Sure one could drop below 10 kph & save the suspension but all the screws in the dash would rattle out & the back ache would kill me driving up & over every single bump ;-) A quality, well set up suspension will handle these speeds as long as the car isn’t grossly overloaded.
Also I've found coil springs are far superior than leaves on corrugations.
Cheers Craig…..
HZJ105, 3.7 tonne loaded, Koni shocks, Lovell springs & over 250,000 km without failure. (Shocks recently rebuilt due to fading)

Not long back from cape york and its corrugations and I found around 60klm to be about right for the smaller corrugations but cannot believe the large ones could be driven at this speed continuously without some lose of control or severe vehicle damage.
The problem with the float on top theory is if you get out and have a look at these things you will see they vary in distance from peak to peak and in depth surely making it impossible to find the elusive sweet spot. In the same stretch they can vary from 1 foot to over two and a half foot peak to peak so you will float over some and drop into others no matter what your speed. I couldn't find a sweet spot anyway so when the roof started going boing I started slowing down
Another problem with the cape, its very difficult to maintain a steady speed due the many dips
We had few problems and I don't really mind corrugations in fact i would rather drive along a heavily corrugated road for hours to a campsite that no one goes to because the road is "to rough" than find myself in a overcrowded camp full of sedans.

God bless corrugations!

Wayne,
Like everything in 4wd'ing. It depends. The nature of corregations change from place to place. Some are hard some are softer, the frequency changes, the height changes, sometimes there are other road related issues ie washouts. There are also factors like tyres, type ie splits vs tubeless, vehicle, loaded mass of vehicle, driver experience..... An endless list really.

Most people drop the tyre pressures. What to varies but it does make sense. You are trying to reduce the transmission of thes forces to the car. Often local info is useful as they may run tyres with slightly higher pressues because of shale etc on the road. Lower is not always better.

As for speed, who knows. I drive on them any where from 30 km/h to 80 km/h. The ones on the north end of the CSR work ok for me at ~40km/h. Some others (ususally smaller) 80km/h is fine. The main point is to stop every couple of hours and let things cool down. Check shocker and tyre temp as soon as you stop. If either is really hot then you are pushing your luck and need to look at tyre pressure/speed combination.

One point that has not really been covered in the discussion so far is the energy that is transfered to components. In general the higher the frequency the less energy. So big slower changes/vibrations may do more damage than smaller faster vibrations. This does not take account of resonance which may rapidly destroy components like circuit boards at any frequency. If you match the resonant frequecy a few seconds may destroy the component. What damage normal vibration does varies as some things flex better than others. I had a Jackaroo and the spot light mounts used to come loose or even fracture within 1,000km. I just did a 10,000km trip in the 79 series cruiser with the same lights and I didn't need to even tighten them up. Why, apparently the lights were specifically designed to go on Patrols and Cruisers.

There is not much doubt that when planing the suspension and tyres are takng a belting. How much of a belting is what everyone is talking about. The trick is not to belt them so much that you induce a failure. If things are getting really hot you are getting closer to a failure. If you go out there expecting corrigations then don't go with worn out tyres. There is a link between tyre condition and it's survival. If you belt a tyre with 2 mm of tread left chances are it will fail on you. I have seen people (tourists) trying to get tyres fixed that have had wires sticking out the side of them they were so worn but they thought they would get a few thousand k's out of them. Strangely, the mechanic declined to repair them.

Lots of people say the shocker brand helps but in reality it changes how fast they fade and how prone they are to failure. If you drive to the limits of the equipment they (mainly) all do the job. On that point, it does not matter how good the equipment, if you drive like a nutter you will eventually go past its limits and bugger the equipment. On that point the last trip I did the only shocker failure were new Koni's. Don't get me wrong, Koni's are good equipment, definitely at the great end of the scale. The truck was overloaded and the driver somewhat careless. You need to watch out for the I've got an indestructable truck syndrome ie the feeling the truck is bullet proof because it had some expensive shocks on it. Belive me that you can break any truck irrespective of how much you have spent on it if you treat it badly enough.

In general you need to weigh up the conditions and the risk of other road hazards and pick a speed and tyre pressure that is not vibrating you car apart and allows you to drive safely on the road. I use the "better to get there late than never arrive" approach. Others do the 80km/h or die in the attempt approach. If you do lower tyre pressures be aware that many high speed tyre failures are due to under inflation and the related heat build up so watch your speed with lower pressures. As always it is your choise, you are the only one that knows all the information in your case.

Steve