Thread: corrugations - fast or slow?

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.

Originally Posted by 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.

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.

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

Originally Posted by ososlo

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.

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.