The pressure written on sidewall or belonging to the loadrating is , as esplained already, not the maximum pressure of the tire. Also saw this pressure needed for the maximum load called the maxloadpressure, and in a formula sheet I got hold of from ETRTO it is called the reference-pressure , will shorten it further to Pr.
But what is that maximum pressure then?
I once concluded of information of semperit ( from continental) wich writes that standing still the tire is allowed to bare 2 times the given maximum load at 1.4 times the Pr ( cold).
Standing still there will be no heatening up by driving, so only by by higher outside temperature in time.
So I think the tire-maker supports a absolute pressure of 1.5 times the Pr.
Or the other way around, they determine the maximum pressure they can stand in for and take 2/3th of that for the Pr.
10 psi higher then Pr is adviced for LT and ST tires in several articles.
LT for more then maximum load at verry low speeds and better handling.
ST for higher speed then 65m/h.
To use the pressure loadcapacity-lists of the tire makers in America is somewhat dangerous.
Best is to use my made lists wich takes care the deflection of the tire stays the same over the whole range of pressure/loadcapacity, wich is the goal of all the calculations, so also of those that are used to make those pressure/loadcapacity lists.
Can be found on my public map of skydrive that belongs to my hotmail adress with same username as here. https://skydrive.live.com/?cid=a526e...E092E6DC%21904
take the USA map and first search for the Pr and open the pdf begining with the Pr. You can pick for per tire/per axle single or axle dual so you dont have to devide by 2 or 4 first.
Then search in that list the maximum load of your tires or loadindex, and in that row search for the axle or highest tire-load on the axle, +10% to get the needed pressure.
Because my calculation takes care of that same deflection , it is allowed to go verry low in the pressure.
But also you can use my motorhome-tire-pressure-calculator to be found in this map
then all the reserves are done automatically, and you will get some extra information about loaddivision overloading and possible weightdifference on the axles. If only GAWR's give they are used , when real ( assumed) axle loads are given those are used.
If advice goes over the Pr but less then 10 psi , the pressure kinds are made red to warn but still ok. If more then 10 psi the advice pressures also are made red to , to warn you are going over the border the tire-maker supports.
Then take your own conclusion about why it needs to be that high.
First download the needed spreadsheet and then open it in Excell or Open office CALC on your computer. For that CLICK RICHT
on the needed document, and choose download from the dropdownbox.
dont leftclick or use open in EXCEL or WEB-APP, first is to complicated and asks you to log in with your hotmail adress, second tries to open it in an excell like program in the cloud and then gives messase that it cant handle some things I used in the spreadsheet.
So topicstarter use my spreadsheet or the lists and se how low you can go savely.