On corrugations, tyres and pressures

We encountered horrendous corrugations (horrogations) on the Mitchell Plateu. They were huge. It was like driving on the ocean with small statiionary waves. A lot of vehicles experienced trouble on the Mitchell Falls road. Most common problem was failed shock absorbers. Shocks became overheated ( actually too hot to touch) and leaked oil. Some vehicles lost control while driving a strait line. This occurred on all types of vehicles. There were other problems. One vehicle lost its aluminium bull bar. Trailers broke axles. Roof racks broke (ours did and the fridge as well) One family told us their children became car sick and the kids had to hold buckets in from of them! I measure the peak to peak length of some of these corrugation. They varried from about 400 to 600mm. Thats 2000 corrugations per kilometer for an average length of 500mm. The Mitchell Falls detour is about 160km return. This eqates to about 320,000 hits. I was surprised to find that the peaks of the corrugations consisted of sand. This could be easily scraped away by hand to reveal a smaller hard corrugation So why are they so hard on the vehicle. Different soil types produce different corrugations. Without exception red soil produces the worst and grey soil the best (smallest, nice and friendly) We soon learned to expect bad corrugations when we saw red soil in the disstance. The iside of a curve was less severly corrugated than the ouside. I also believe the peak shape is not symetrical. Often on an out and back journy driving times were different. I tried testing the theory by driving on the wrong side of the road. Diddnt seem to work. Corrugations became worse at the end of a tyring days drive, the fatigue factory. Or when there was something wrong with the vehicle , the worry factor. By the way the Mitchell Falls are simply superb. Better than the glossy magazine photos But i wont do it again unless the grader is in front of me. I played around with tyre pressures. I usually run 65psi or more on bitumen. I deflated to 50 psi on general dirt. On the sever corrugations i tried 45 psi then down to 38 psi with no noticeable difference. Maybe my 14 ply tyres are too rigid in the side walls ,i dont know. I prefer road tread tyres. They are less noisy, pick up fewer stones and last longer than lug tread tyres. They have more rubber on the road per contact patch, dig fewer holes in soft ground and steer better as well. In mud they clog in one revolution, the same as lug tyres. Regarding shock absorbers. Take spares and buy the best (Konis) Dont buy American, or the popular 4WD aftermaket yellow ones as they will fail. Take spare rubber bushes. These can get hot and fall apart. I fitted duel shocks (ie two per whell) on the OKA and they only just got warm from then on. Vidas