The more load that the vehicle is expected to carry, the more pressure that
the tire is expected to be inflated to. At the maximum loading limit, you
will also find the maximum tire pressure limit. But if you take the tire to
its maximum pressure limit without taking it to its maximum load limit, it's
not like as if the tire is going to explode due to not being put under
enough load.

It will just have its outside tread edges a little off of the ground at
worst, resulting in overinflation wearing patterns on the tread. But that's
actually what we're after here. We want the tire to pop out a little bit,
before we return it to its normal pressures.

   Yousuf Khan

do you work on your own car?

have you checked the tire pressure while the wheel is jacked up off
the ground vs. when the car's weight is on it?

if not, go do so and come back and tell us if the pressure reading is
different.

i'm going to say this one more time: the doorsill pressures can be
realistically taken as the minimum recommended pressures for the
tires.  below these pressures you can dangerously overheat your tires
and cause a subsequent catastrophic failure.  however, for very short
term use (on soft surfaces, on a drag strip, etc) dipping below these
pressures may be tolerated.

the sidewall pressures may be taken as the maximum recommended
pressures.

it is _extraordinarily_ likely when using the doorsill pressures that
during hard cornering manouvers the shoulder of the front tires (which
see the most extreme sideloads and weight transfer) will be rolled
over and the contact patch of the tire distorted.  this is immediately
identified by wear on the shoulder past the tread.  without **any
question whatsoever,** increasing the tire pressure, up to the max
sidewall pressure, will decrease this effect and net an increase in
lateral accleration performance.  the tires will hold their shape
better and much more vehicular control will be available to the
driver.

though this condition will generally result in greater center tread
wear, it will also result in less shoulder wear.  these two wear
conditions must be balanced on a case-by-case basis.  as i said
before, if you don't push the car through corners, then you won't be
rolling on the shoulders and you won't need to increase tire
pressures.

americans drive lincoln town cars and like a cushy, mushy ride.  tire
pressures are ALWAYS a tradeoff between ride quality, tread life,
economy (rolling resistance), and traction.

contrary to what some armchair drivers would have you believe,
increasing the pressure of the tire up to the sidewall pressure does
not result in miserable braking and accelerative performance.  this is
readily verified by GOING OUT AND TRYING IT YOURSELF.

for more information, see page 10 of
http://www.tirerack.com/images/tr_ownersmanual.pdf

l8r
ken