[AXMonster]

At a guess, I'd say that passenger car tyres are designed around the max inflation pressure that can be used at the tyre's rated loading at its rated speed.

i.e. 51psi at 1350lb at 130mph.

These figures will be initially simulated during the design stage, then proven out with correlation testing, then real world testing.
A factor or safety will be designed in (possibly around 1.5 to 2, and I'd guess no less) to account for deviances in manufacturing tolerances and materials specifications between batches.

The testing would include kerb and pot hole strike cycles at specific speeds, with a required number of cycles before failure i.e. 10,000 cycles to failure pass rate. These would be tested on new and aged tyres to determine any age related degredation.

Testing would begin at a baseline predicted by the FEA simulation, then change according to the test results and failure rates. From all of this the result would be a homologated tyre that passes the required tests and would be given a load rating, speed rating and max inflation pressure based on the test results.

Its a bit of a wired science, but more and more tyres are being designed for specific vehicle models these days.

If you fit a tyre rated to 1350lb and 130mph to a car that can only do 110mph and has a corner weight of 600lb, then at a guess you'd be reasonably safe increasing the max pressure over the limit on the sidewall...... by how much I don't know, but a few psi probably wouldn't put it into the danger area?