corrugations - fast or slow?

[Leo]

Good day all,

I know that not all corrugations are the same, anyway, on a trip this past weekend the car (RRS) was smoothest at about 70 - 80km/h on a corrugated dirt/gravel road.

So am I right in assuming that speed caused less damage/ wear than driving at say 50km/h but being shaken to bits?

Also noticed a massive difference between normal mode and grass/gravel/snow or 'mud and ruts' with regards to stability on a road with smallish gravel 'marbles' that had been swept off the driving line to the edges. Did most of the trip in normal mode but swithed to ggs after going through an off-camber bend sideways. DSC pulled the car straight alot quicker than if it wasn't there, but in some situations it killed power when needed.

Cheers!

[bbyer]

I have found that mud and ruts is good for loose snow so perhaps loose gravel as well. The GGS seems to me more for hard slippery surfaces such as ice, but I suppose packed gravel qualifies.

Either setting is generally better than normal for anything other than pavement.

As to speed, I know real slow and big bumps can be wrong as the suspension never gets to "work", hence I can believe that 80 kph with flying rocks and lots of dust is easier on the vehicle than 50 kph, plus everyone can see you coming, that part is for certain.

Also, one definitely wants mud flaps installed.

[Graeme]

So am I right in assuming that speed caused less damage/ wear than driving at say 50km/h but being shaken to bits?

I'd say so. The shocks would be working harder but I'd prefer to wear them out than end up with a vehicle shaken to pieces, let alone the improved occupant comfort. The ride may be better again with a small lift to get a bit more suspension travel to avoid occasionally hitting the bump-stops.

[bbyer]

I'd say so. The shocks would be working harder but I'd prefer to wear them out than end up with a vehicle shaken to pieces, let alone the improved occupant comfort. The ride may be better again with a small lift to get a bit more suspension travel to avoid occasionally hitting the bump-stops. Even though I say I do not need a higher ride, that hitting the bump stops comments has me thinking.

In spring, our City "paved" streets are a war zone of pot holes so banging down on the bump stops is common just on a normal "go get milk" run.

Shocks here are more often broken by continued hitting the bump stops long before they die of normal use.

That, and I am starting to understand the new recovery feature - it sounds like assuming no mechanical problems, (failed air compressor, broken air airlines), just electrical, that the recovery mode should get the 3 back up to at least normal height from an electrical induced fail to the bump stops situation?

[big guy]

The biggest problem with Landies or modern 4wd's in general is that they absorb and hide the rough ride so well, you never really know how hard the suspension is working which can be very tricky.

On one of my trips I drove my mates D3 and he had my D1.
When I got out as we stopped for photos all the time(tourist), I was fine and he commented on how rough the corrugations were.
I said really? So I felt my shocks(Bilstein) on my D1 and Yes--they were working thats for sure.

He said it reminded him of the army days. I always thought my ride in the D1 was wicked but rightly so, its ordinary compared to the D3/4. I does however make you realise that the suspension in all cars are working hard to keep up, its just that some show it more and it could well be a good thing so you slow down or find a comfortable speed.
We later went on a fire wood run and took my car D1, we sat on 70km'h on the corrogations and he said that was totally different ride on same road as it was when I was lead vehicle and sat on 60km/h. So each vehicle depending on tyres/ pressures and settings will have a different sweet spot for speed I found out.

[rmp]

The bigger issue is vehicle controllability. It is possible to get a relatively smooth ride at high speed, because you're skimming the tops of the corrguations.

But good luck trying to control the car at that speed.

For me, the best speed is the one at which there is least bouncing and I retain the ability to control the car.

Reducing tyre pressures helps. How far depends on the state of the track. For example, the Perdika track is one of the worst roads I've driven and we dropped to 20psi for that. Higher-speed dirt roads maybe 25, 30, all dependent on weight, tyre construction and especially speed.

[clubagreenie]

I remember a few trips out north of Oodnadatta one in a RRC and the other previously in a S2. I know not much comparison but no matter what speed in the S2 you get shaken. In the RRC 80 was great, as it is in the D2 I have now, but as mentioned good luck with control as you can feel it floating on top of the road. It's like a feeling of understeer turning into a curve but as you go through it you have to watch not ending up drifting the back out.

[juddy]

I have found 80/100k fine on corrugations, however you have to be mindful of controlling the vehicle from time to time, and having a wider track road will help with a slight loss either side. As for tyre pressure i never once let the tyres down, some say you should other not, maybe it depends on your tyre type. You do seem to skim the surface when driving at a higher speed, but you can still get shaken from time to time on the different types of corrugations that seem to appear, and a slower speed is then required, and i bet the ride in a RRS or D4 etc will be very different to a Defender.

[PhilipA]

80Kmh "skimming" is far harder on the suspension than going slowly . Graeme would probably change his ideas about preferring shocks to fail if he was stuck at Drysdale River for a week or so waiting on new shocks.

My experience is that you can skim up to a certain level of corrugations and after that you just have to slow down. And my theory is that the level of corrugation depends on the size and amplitude of the corrugation.
The worst corrugations I have experienced were on the Kalumburu road, Mitchell falls road and ABC Bay track.

On all of these I had to slow to maybe 15-20Kmh as there was no speed that was "skimming"
These were in all cases caused by tourist 4WD buses who did not air down and created a corrugation about 100MM high with spacing of 150MM. These corrugations in my 2inch lifted RRC with Bilstien shocks seemed to cause a resonant frequency. I assume this as all roads lead nowhere and do not carry many heavy trucks.

I spoke to 3 separate people who were 200 LC owners , who had actually destroyed front shocks on these roads by the tops blowing out, and all had travelled fast ie 80Kmh.

BTW the ride is much smoother even at lower speeds if you knock say 6-10PSI from the tyres , in mine about 22-24 front and 30-32 rear. I set a max of 85Kmh at these pressures and had no problems in over 4000Km of dirt, and towing an off road camper whose tyres I knocked down to about 18PSI because it is light.

So IMHO , decisions should be made according to the conditions. The one thing I would say is slow down when you see a car approaching. There is nothing that rates you as a City Arsehole more than passing a car from the opposite direction at 80Kmh and possibly breaking their screen.
Regards Philip A

[ososlo]

It reminds me of travel thru the Serengeti...A hell road for corrugations..We were in 300tdi discos and seldom out of 3rd gear for days on end...We were overtaken by a Toyota troopie..one of those game spotting type wagons that was trying to find the harmonic balance to speed across the bumps..

All to no avail as we passed him some time later with the rear shock mounting smashed off.

So it pays not to underestimate the work your suspension is doing..

As it was we went through two sets of shocks and even got one set flown in overnight from Arusha.

Common sense must prevail and as an owner of a D1 and a D3 the difference between driver comfort is a world apart

[Graeme]

That, and I am starting to understand the new recovery feature - it sounds like assuming no mechanical problems, (failed air compressor, broken air airlines), just electrical, that the recovery mode should get the 3 back up to at least normal height from an electrical induced fail to the bump stops situation?
Sorry, but no height sensor trickery either mechanical or electrical can cause the suspension to raise if the system has dropped the vehicle to the bump-stops.

[scrambler]

As I was taught it in what must now be the Dark Ages, the reason for the "harmonic" smoothness is just that - the vehicle is "in sync" with the corregations. If the corregations are fine and the harmonic speed is low (say 30km/hr) you can increase the speed, usually to twice the initial speed and achieve smoothness again. Two different vehicles will have different harmonics, two different corregated roads will as well. For each vehicle and each road you start slow and increase to a safe maximum speed looking for a smooth patch. The shocks might work harder at higher speed but the steering response is better.

This advice is more useful to those of us with live axles than D3/4s but the same principles remain. I would expect that something like changing ride height, or damper settings, would change the harmonics leading to better handling at one speed and worse at another.

At the opposite end of the technology scale, I can tell you that a leaf-sprung Suzuki Sierra MUST be drive at a harmonic speed unless you intend to be "shaken not stirred" for the entire trip.

[Graeme]

80Kmh "skimming" is far harder on the suspension than going slowly . Graeme would probably change his ideas about preferring shocks to fail if he was stuck at Drysdale River for a week or so waiting on new shocks.
I said wear out faster, not fail or destroy! I was regularly the slowest vehicle in a group of vehicles that crossed Madigan's, being particularly concerned about not damaging my loaded vehicle from the extreme suspension articulation that was occuring, but have no hesitation in driving at a smooth speed over corrugations as long as its not so fast as to not have sufficient control. I also replace shocks as soon as they show signs of no longer working effectively and expect never to be stuck because my shocks are worn-out. Maybe not driving an LC200 also helps.

I found the Perdika track just a little rough too.

[CaverD3]

Can't really say they seem to have graded all the corrugations since I got the D3! :D

[Leo]

It reminds me of travel thru the Serengeti...A hell road for corrugations......

Just got back from the Serengeti when I made the original post!

The road's a lot better now up to Ngorongoro- very smooth tarmac until the gate. The corrugations start after the descent into the plains and go on for hundreds of kms. The dirt (never graded) tracks are smoother!

Car was ok, but the front windows now rattle when the doors are shut, or when partly open and driving over bumps. Apart from that, only damage was a slightly damaged rim, suspension squeaks a bit sometimes, one of the headlights points down and some of the seals are not as dust-proof as when new.

Was a massive difference compared to the last time I did the trip in a Defender 130 - never felt tired or uncomfortable even after hours of driving.

Thanks for all the replies, learned a lot.

[Scary]

We just drove on some nasty diffreing sized corrugations on the weekend - the smaller distance between the corrugation peaks made it smoother to run at around 80-100 whereas with the larger spac you could feel the wheels drop into the low so drove slower.

Interestingly I drove in std mode most of the way and the DSC was happy for me to slide the car a bit on the pea gravel before braking indiviual wheels to bring the cra back in line - turn in was alot more responsive

In Gravel mode the cra understeered 1st without qustion and was alot more aggresive when the DSC cut in and quit frankly I did not enjoy it so it got switched off - I also drive rally cars on gravel so I like to feel the car moving and have as much turn in as possible so the gravel mode made the D3 feel like a badly set up car.

[rmp]

Grass/Gravel/Snow is one mode I almost never use, and have never on a dirt road. The car becomes far too dead and unresponsive for my liking. I appreciate it would be fine for those not used to driving on dirt or uncomfortable with a bit of slip, but I always use Normal for dirt roads, almost always with DSC on. I switch DSC off if things get really slippery, eg snow on the road and lower speeds. I remember once being followed by someone in a D3 (forum member here actually) who could not understand how I could accelerate on a mud/dirt road. Answer - DSC was off! But that only works if you're comfortable with the car moving around a bit and correcting it as required.

The bottom line is that, fundamentally, some roads are just bad and that needs to be accepted and endured.