I cant help myself, I've got to jump in having just read about 75% of this thread.
1. Vehicle and tyre manufacturers spend years testing vehicles with tyres and pressures that achieve the best compromise of handling, ride and tyre durability - especially commercial vehicles - if you think you can do better than 750,000 to 1 million mile testing then you should be building vehicles.
2. They take the bother to stick a tyre placard with tyre and pressure options at max legal weight of the vehicle's axles. eg 60psi front 65psi rear for 215/R15 or 55psi front 60psi rear for 205R15.
3. The tyre placard lists the only tyre sizes that can legally be fitted in many countries and may also state the max axle weights for each tyre size/rating if there are options.
4. In some countries your vehicle will be considered unroadworthy if the tyres don't match the tyre placard, rare but if you get a full inspection its an easy one to pickup.
5. Dual tyres running soft are dangerous as the side walls of the adjacent tyres will touch and overheat/fail.
"A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse (defined as a liberal gift) from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, followed always by a dictatorship. The average age of the world's greatest civilizations has been 200 years." - attributed to Alexander Fraser Tytler, (October 15, 1747 - January 5, 1813) a Scottish-born British lawyer and writer.