I now realise that I am writing to a Travel-trailer forum , thougt is was for motorhomes because of the RV in it.
So I will give the direct link to the map for the caravan/trailer calculator.
Yust recently chanched it a bit , added American English in wich preset is 10% tonge-weight ( give me a better word and I will change it).
This is in Europe , so the other languages , 4% because the axles are placed more to the middle of the box here.
But you can give in the small orange cell your own lbs and it calculates the % for you.
https://skydrive.live.com/?cid=a526e...E092E6DC%21348
But if you want to read the article of J.C.Daws, about tirepressure at reduced loads, I have it on my public map too, navigate to the head map, but better get it from his own site
http://www.dawsengineering.com/desite4_003.htm take the 6th dot .
Hover to page 11 for the discussion and the conclusions, I wont ask you to understand the rest, some Equations I cant follow either.
I think the article wil acnowledge things you wonder about too.
So you see , I could write a book about the used systems and what is done wrong for tires maximum load and calculation of pressure all over the world.
The tire-makers know this, but dont want us to know.
And its the reason for regulations by law for having TPMS in the car , and the higher adviced pressures after 2000.
To my opinion an overreaction to the tire-failures courced by to low calculated pressure. In Holland institutes write that 50% uses to low pressure, but if you would look at wich pressure is save , only 10% to low pressure would be left of it. Its yust what you use as reference.
In the map "all about tire-pressure" my last spreadsheet "pressureloadcapacitylistandconversion " in wich 4 tabs at the bottom.
1st is to make graphics of different calculations.
2nd is to compare differrent calculations or tire tipes, but also little history about the used formula's in time. Made my own universal formula, from wich the old and new can be made, and give the different Power and construction-load used in time, and what I think is the X and Lc that have to be used to get the same deflection over the whole range.
3th is to converse to other market, with other Pr system and weightkind, and to make your own pressure loadcapacity list for one tire.
It gives 4 lists in every used pressure and loadkind( PSIand bar/kpa,and KG Lbs) to copy to any other file.
4th is the disclaimer of 3th.
Play with that spreadsheet and get wiser.
https://skydrive.live.com/?cid=a526e...E092E6DC%21601
Dont worry , I will stop now
Greatings from Holland
Peter