Richard Tarara is correct that it is overall force or weight of the trucks that
breaks up our roads and not pressure. The reason is that the weight of the
truck bends the pavement. It is the stresses created by the flexing that break
s the pavement. When the road bed is water saturated it flows especially well
and offers minimal support for the road surface. Thus, more flexing. This pro
blem is most serious during the spring thaw because the upper part of the road
bed thaws and turns to mush while deeper it is still frozen, preventing drainag
e.
While it is true that the sidewall of a tire supports some of the weight of
a vehicle, the majority is supported by air pressure, especially with radial
tires. We have our auto tech students run a car onto pieces of paper, trace
the "footprint", calculate the area, multiply by tire pressure, and compare to
the weight of the car. The result is usually within a few %.