Tire pressure, 2000 Land Yacht 355XL

[EngiDent]

Hi
2000 Land Yacht 355XL, F53 chassis
Wasn't sure which forum to post this in because it has a flat front and is an XL, but is also a Land Yacht.
Owner's manual says 65psi for tires, but everything I've read elsewhere suggests people are running in the 80's. Why is the manual suggesting such low pressure?
Any suggestions for reaching rear valve stems, or a particular extender kit that might work?
Thanks
Dave

[jadatis]

To get a better picture this " pigheaded Dutch selfdeclared tyrepressure-specialist " would like from tires next.
1 maxload or loadindex
2 kind of tire to determine referencepressure ( behind AT ) , probably 65 psi D-load .
3 speedcode or maxspeed of tires.

Configuration of motorhome.
Think 2 axles ,rear dualload.
GAWR'S and GVWR, and if you ever weighed fully loaded those real axle( - end) loads

Then I will calculate my advice, and show how I do it, so you mayby understand better the to your idea low pressure.

Even extenders exist so you can fill inner and outer tire at the same time, and pressure of both will be exactly the same.