The calculation of 342 psi is a static calculation.  The reality is that
when a truck is moving the dynamic forces on the roadbed are thousands
of times higher, and multiple axles multiply the number of dynamic
"hits" on the pavement.  This is why an overweight load can cross a
bridge that is rated for much less weight if it crawls across at 5 mph.

This is also why potholes get bigger.  When you or a truck hit the hole
the wheel is tossed up and comes down just beyond the hole, and soon the
hole is longer.

Trucks pound the hell out of the roadbed, but up in the northern
latitudes or mountains where studded tires are allowed we normal vehicle
drives carve two trenches in the pavement.  These can fill with water
that freezes and be very hazardous.

No easy solutions, only repaving for megabucks.

LAWS HOME wrote:
>
> Did I hear someone dissin' big trucks? *The highway is so abused by heavy
> trucking that the slabs are now bowed in the
> middle, exagerating the contact point at every expansion*
> While it is true the interstates  are in bad shape I must admit we have much
> heavier trucks up here in Mi. Not that our roads are any better, ( probably
> not) , However it's not always the trucks that cause the trouble with the
> roads. In fact if you take the gross vehicle weight of a Michigan train
> 160,000 and divide it by the square inches in rubber that contacts the
> ground on a truck designed to carry this weight (11 axles, 10 wich have 4
> tires each and the front 2 which have a pair of oversize 14" wide tires )
> Given these figures and just assuming that only one inch of the tires hits
> the ground for the entire width ,( this is not true MORE than an ich of the
> tires hit the ground, this is just to show my point) then you will have a
> tractor pulling two trailers and only putting 341.88 psi. on the road
> surface!

Stuart MacMillan
Manager, Case Program
800-909-8244 ext 208

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