Reintroducing an earlier topic, What causes the “washboard” effect on unpaved roads?, I’ve come across some more information on the rather annoying phenomenon.
Scientific American ran an article in January, 1963, entitled Why do Roads Corrugate?, by Keith Mather (p128-136). In the article, Mather examines the factors that create washboarding by building a circular test rig and running a wheel over various surfaces until the washboard surface develops.
What Mather discovered is that, contrary to what was believed at the time, washboarding is formed by the wheel bouncing along the road surface, rather than the wheel pushing a mound of material in front of the wheel then climbing over it. He also found that faster speeds produced washboarding more quickly, and there appears to be a minimum speed at which washboarding will not occur. Hard or soft tires also play a role, as does the vehicle weight and spring stiffness.
As to why different vehicles produce similar corrugations, Mather writes,
A fascinating article that’s worth tracking down.
–Patch
