I once got hold of the European way to calculate advice-pressures for car-tires.
Worked it out and learned myself Excell to make spreadsheets for it.
In my search I came by articles about it .
But the surface on the ground is for a radial tire almost rectangular ( sorry for eventual misspelling, native speech is Dutch).
You can look in the next map on my skydrive of hotmail address, where I placed spreadsheet to calcuate the indentation of the tire for given maximum load and sises.This spreadsheet gave less indetation then it is in practice, and so I also made a picture with paint about how it to my opinion really deformes the tire
This map I opened especially for discussion I have with maker of article about a new way of calculating in which the indentation has to stay the same at lower load.
His article You can find navigating my complete public map with a link in my own first reaction there, Tire-pressure at reduced loads by J.C. Daws.
To make a long story short , mayby by studying my map and the article of mr Daws, you will get a good idea of what is important for the load of a tire.
http://cid-a526e0eee092e6dc.office.live.com/browse.aspx/.Public/all%20about%20tire-pressure
If you can't open a spreadsheet in the browser, download it and open it in Excell or compatible programm, to work with it.
The browser can't handle sheetprotection and data-validation I used in most of them.
If , after reading, questions pup up , ask me here