Depends on the weight you have. Many overload their vehicles, many don't. If your within your vehicles GVWR then use the Ford door jam figure. If your over the GVWR's of your vehicle I'd use max PSI for your tire.
Then we have the old chalk test right Marty :B
2015 Tiffin Phaeton Cummins ISL, Allison 3000, 45K GCWR
10KW Onan, Magnum Pure Sine Wave Inverter
2015 GMC Canyon Toad
Previous camping rig
06 Ram 3500 CC LB Laramie 4x4 Dually 5.9 Cummins Smarty Jr 48RE Jacobs brake
06 Grand Junction 15500 GVWR 3200 pin