Name any gravel road and we'll guarantee it has corrugations - they might be so small that you don't notice them or big enough to bounce your internal organs up to peek out of your eyeballs but they'll be there. Even a freshly graded road will have corrugations waiting to re-emerge a little further with every tyre that passes over.
Dr Karl, of the ABC Science Show (abc.net.au/science/drkarl), tackles the subject of how corrugations form, ranging from Keith Mather's experimentation with corrugations at the University of Melbourne in 1962 to a raft of potential causes observed by his enthusiastic listeners.
Many seem logical and the reality is that there are probably multiple causes from the impact of wheels hitting bumps and thumping down to create ever bigger valleys; or the effect of suspension bounce from skittish lighter vehicles; braking and acceleration, to the inescapable impact of Mother Nature as winds blow sand into mini dunes.
There's no doubt that you just have to learn to live with corrugations if you plan to head off the bitumen.
Rule of thumb for driving on corrugations is to reduce your tyre pressure by about 15-20 per cent of normal hardtop running. With each reduction in pressure, there should also be a reduction in speed. It will reduce impact on the road surface a little and ease the strain on suspension components.
Next, vary your speed to see if you can strike a safe balance sufficient to allow tyres to "float" over the valleys by skipping across the bumps. Too slow can be bone shattering, too fast and you'll risk losing control.
As a guide only, totally dependent on your vehicle, the load it's carrying and the road conditions, your optimum speed could be anywhere from 50-80km/h - lower if you're towing a heavy off-road camper.
If you have a long run on corrugations, stop regularly and look at the tyres and suspension.
Place your hand on each tyre to identify temperature variations. If one tyre is significantly hotter, it could be losing pressure. Corrugations compound heat generated in an underinflated tyre - potentially to the point where the tyre will blow. Always carry a tyre gauge to check pressures or fit a tyre pressure monitoring system to continuously monitor pressures from the driver's seat.
Remember that if you're finding the ride uncomfortable, your vehicle is suffering even more - shock absorbers can rapidly overheat and a regular stop provides time for components to cool down. Check for loose bolts at each overnight stop, particularly on aftermarket accessories - losing your roof luggage or a spotlight at 80km/h can put a major dampener on the holiday.
Keep in mind that corrugations and bulldust seem to be inseparable - the fine talc oozes into the seals amazingly fast. Apart from creating a major cleaning headache, bulldust can fill large and all but invisible holes. It's a nasty surprise if you drop a wheel in at speed. Watch for subtle changes in the track. Bulldust holes are a harsh reminder to stay focused when driving on the gravel.