Corrugations - Fitness Program or Destructive Test?
Originally published in OutdoorX4
If the claims of weight-loss vibration machine purveyors are to be believed, then overlanders would be the slimmest and fittest demographic in the world. This is due purely to one road feature we spend so much time driving on — corrugations.
Anyone who has driven or ridden in a vehicle on dirt roads has experienced the harsh vibrations that corrugations—or washboard—can impart to a moving vehicle. These vibrations can be damaging to the vehicle, causing fittings to come loose, wires to chafe, mounts to snap and any number of other problems. Safety is also severely effected as the wheels are not in contact with the ground all the time, so steering acceleration and braking are all compromised, to say nothing of the fatiguing effect on the vehicle occupants. Given the dangers of corrugations, what steps can we take to mitigate the bad and make the experience as good and safe as possible?
Driving position — This should be a given, but to reduce fatigue make sure your seating position is correct. Seat up-right enough to support while allowing easy and comfortable reach of the controls. People vary, of course, but a good general rule is to be able to reach the top of the steering wheel with your elbow slightly bent while having your back fully supported by the backrest.
Tire pressure — Lower pressure on all tires, including trailers. The oscillations caused by corrugations are so fast that any extra damping is a great thing. Also the increased contact patch allows for greater control in these compromised circumstances. Pressure will vary by vehicle and load, but as an example, for a loaded Land Cruiser in Australia (approx 6700 lbs) I ran my 265/75R16 Toyo Open Country ATs at 18 psi in the front and 22 in the rear (around 50% of street pressure). The trick is to get a similar bulge on the sidewalls front and rear. Some would argue that my pressures were too low, but that leads directly on to . . .
Gentle control — Brake, accelerate and turn gently. Aggressive maneuvers can lead to disaster when the tires are contacting the ground only part of the time and also when pressures are low. This means you have to stay alert and drive predictively. Look ahead for obstacles, slow preemptively for corners and do so by either coasting or applying brakes very gently. Accelerate gently out of corners. Imagine an egg between your foot and the pedal and apply pressure so as not to break the egg.
4WD — Back in the 80s, Audi definitively proved that four-wheel-drive was better on dirt. They crushed the World Rally Championship with the Quattro, a vehicle that was more stable and sure-footed than any competitor due to being 4WD. There is no reason not to gain all the stability, handling and tractive advantages of 4WD if you are on dirt roads, so lock the center differential if you have one or select 4WD for part-time systems. And don’t forget to lock hubs if you have them.
Pick your line — Sometimes it is unavoidable to drive in corrugations, but sometimes you can minimize the effect by straddling ruts or using the opposite side of the road. Even riding up the side of ruts can help, but be aware of your sidewalls and keep a sharp eye out for oncoming traffic.
Find the harmonic — At certain speeds corrugations will seem to smooth out. This is due to the tires skipping from the crest of one raise to the crest of the next. While the ride is smoother, contact with the ground is severely reduced. This usually happens between 25 and 50 miles per hour. If you find the harmonic speed, try to maintain it as evenly as possible. If you have followed the guidelines previously laid out, you will be in the safest condition to take advantage of the smoothed out ride.
Corrugations are an unpleasant fact of life for overland travel. These are just a few tips to make them more pleasant and easier to deal with. And who knows, if the vibration machines work you may loose weight and get a workout at the same time.