Just to add to Grit dog's point - look into the owner's manual of German sport sedans, often you'll see multiple psi specs, one for each speed and payload bracket. Even in my subcompact Mini, the range goes from 35psi (low payload, under 120 km/h) to 50 psi (max payload, 220 km/h top speed).
That's an example of the OEM engineer trying to tailor a design spec to each end user application. In Germany, probably the most engineering oriented culture, it works.
In our sue happy North American culture where people never read a manual, and talk to their lawyer the minute their tire blows, OEMs are forced to take a different approach.
