Originally Posted by ecobeest
My 2012 came with LT245/75/R17 Load Range E. Max inflation from the sidewall is 80PSI.
TRA = Tire and Rim Assn. That's a bunch of engineers hired by the auto and tire industries to test and publish the results of their tests as to proper tire inflation for the load on the tire.
Ignore what Jim and Susie are running, and go by the TRA load/inflation table for your size tire. That means you must weigh the wet and loaded rig on a CAT scale to get the weights on the front and rear axles of the truck. Then weigh it again when not towing and get the weights on the front and rear axles of the truck.
Divide the weight on the axles by 2 to get the approximate weight on each tire. Then apply the load inflation table, using the PSI for the next higher weight.
The TRA tables are hard to find for cars and light trucks. Most tire manufacturers now just say to go by the vehicle manufacturer's weight limits. But if you look hard enough, you can find the TRA tables. Here's one source:
Scroll down to page 23 of 28 and look for LT245/75R17E on single axles (not duals). That's page A12 of the full document, but Toyo didn't publish the whole document.
Here's what you'll find as the load/inflation table for that size tire:
PSI . max weight
__ . ___________
35 . 1770 pounds
40 . 1945
45 . 2110
50 . 2270 (max for load range C)
55 . 2430
60 . 2595
65 . 2775 (max for load range D)
70 . 2900
75 . 3050
80 . 3195 (max for load range E)
Your truck weighs 3300 pounds on the front axle and 4680 on the rear axle. So that's 1,650 on each front tire and 2340 on each rear tire. So for that load, you need 35 PSI in the front tires and 55 PSI in the rear tires. If I had those weights, I'd probably add 5 PSI and make it 40 front/60 rear. More PSI than that and you'll wear out the center of the tire tread prematurely, plus have a harsher ride with no benefit to the higher PSI.
Apply the same logic to the unloaded weights of your truck. Don't go below 35 PSI, but there's no need for more PSI than the TRA table calls for.
As you can see, Ford put plenty of tire weight capacity on the F-150s with HD Payload package. The GVW for the above example is 7,980 and the GVWR of the F-150 with HD payload pkg is 8,200. And the above example is a real-world 2012 F-150 EcoBoost SuperCrew 4x2 towing an 8,000-pound fifth wheel RV.