what is the role of varying tire pressures

[Jerry]

From the Dunlop Tire Tips web page:
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For touring motorcycle loading, follow these general guidelines:
Light loads-single rider with some luggage (up to 200 lb. total)-minimum tire pressure of 32 psi front and 36 psi rear must be maintained.
Heavier loads-dual riding and/or luggage (from 200 lb. total up to maximum motorcycle capacity stated in the owner's manual)-pressure of 36 psi front and 40 psi rear must be maintained.
Please Note:
For any dual riding or fully loaded use, 40 psi must be maintained in all Dunlop rear tires fitted to touring motorcycles.
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Howerver, for the new Elite III (E3) the base recommendations are 30 psi front, 32 psi rear. Max weight carrying capacity comes in at 40 psi for both tires.

From this, I would experiment from 30 - 36 PSI front and 32 - 40 psi rear and see what feels best to you. (Would not go below these figures for any reason.) On my Elite IIs I run 36 front, 40 rear. I weigh 265 and have a Vetter with hard luggage (no trunk) so am definitly in the "fully loaded use" range!

[Pat Kelly]

The general "rule of thumb" that I learned roadracing and still use:

Adjust tire air pressure to get a 10% rise in air pressure from cold tire to warm tire.
Example:
cold 30 psi, when warm 31 psi. Tire needs less air. If it is dropped to 29 it should warm up to 32, about perfect.

This takes into account ambient air temp, road temp, load on the bike.
It seems like a lot of work and it is at 1st. After awhile you can walk outside, feel how warm/cold it is, guesstimate the riding weather later in the ride, you know if you have a passenger or load to carry or if solo. Bump the pressure up or down 3 or 4 psi and you're good to go.

Of course with racing you needed the tires to warm a certain amount so they would stick in the corner when riding 10/10ths. Too warm and they might not last a full 6 hour race. Too cold and you may slide out in a turn.

High pressure = lower tire temp = less psi increase,
low pressure = higher tire temp = greater psi increase.

Of course if you can afford a tire temp probe............ ( can't)....