[s-cars] wheel offset calculator program ~ tire pressure calculator and adjustments for "plus" sizing

[mlp]

Which prompts a related but different tire topic question.  
Other than the generally accepted "Get a pyrometer kid.....," 
Does anyone know of any rough rules of thumb (aka ROT) as a place to
start from for roughly targeting, adjusting or estimating appropriate
tire pressure settings for substantially changing tire width(s)?  
i.e. going from stock 225/50 to something like 245/40's or 255x40's?

Somewhere I've seen a post tossing out an opinion along the lines of
add +2psi or 3psi to your OEM recommended pressure for each +1 size 
increase...." but that just doesn't make sense to me if what one is
looking at is the tire contact patch.

A little different issue from the above, but last week a couple of the
Audi Club instructors for the Winter driving event held at Steamboat
started playing about with snow tire pressures to see how much effect
they could detect on snow tire performance.  The consensus seemed to
be leaning towards, at least while on snow & ice, slightly lowering 
pressure by 2psi~3psi from @ 36, or so seemed to help.

Any list wisdom or guidance out there, or directions on where & how
to use a tire pyrometer properly to read a tire temperature curve?

Thanks
mike

>-----Original Message-----
>From: s-car-list On Behalf Of Jeremy Ward
>
>Hey gang.  I was asked some really difficult math .....