Though best is, as already written, is going from weighed seperate wheel(pair) weights , second best axle weights, as long as you did not do that, you can go from the GAWR's and add 10% for reserve.
You can find those GAWR's for front rear and tag often on the same plate as the original pressure advices.
Most motorhomes have a pretty constant weight and weightdivision, and often the axleweights around the GAWR's ( gross axle weight ratings, so what is maximum allowed to weigh).
A tag axle is to my knowledge an axle that can be put more or less pressure on the suspension , and even can be lifted off the ground .
You can chanche the division of total weight on the axles with it.
If you highen up the pressure on the ground of tag, less weight on drive axle and more on Tag and front axle.
This is when tag axle is placed behind the rear/drive-axle)
And the other way around , less tag-pressure ( so not the tirepressure of the tag tires) more on drive and less on tag and front.
You can use this if front or rear proves after weighing to go over gawr. and the other axles have a reserve.
If you can give me the configuration of your vehicle and the tire-data read from the sidewall, I am able to give you an advice pressure, calculated with spreadsheet I made and wich uses reserves and and extra save formula .
Need from vehicle next:
GAWR Front REar TAg, better weighed axle loads in the loading you use).
Howmany tires on the axles ( probably front 2 DRive 4 and tag 2).
And where the Tag is placed , behind drive axle or between front and drive axle.
ideal would be if you give your maximum used speed and wont go over for even a minute.
From tires I need at least the maximum load or loadindex, and the Pressure behind AT ( yours probably AT 110 psi = G-load/LRG or European notation 14 ply/Plyrated.
Or read from sidewall something like this "maximum load xxxx lbs AT yyy psi( cold).
Also would be nice if you can find the speedcode of tire,, but on american tires not always given, letter mostly L(max 120km/75m/h) M( max 130km/81m/h or N( 140km/87m/h) for these large , in fact truck tires.
If you can produce that data, I can give you an preliminary advice , as long as you did not weigh.
Greatings from a "Pigheaded Dutch Selfdeclared Tirepressure-Specialist"
Peter
