MetalDog
Junior Member
Federal law says they must put the manufacturer recommended pressure on the door pillar. For 2019 6.4 with 18 inch wheels it is 80 rear 70 front. You must fill them to that amount to reset the TPMS then I would not drop it below 10 psi of recommended. 70 rear 60 front or you get the TPMS warnings. Additionally going too soft reduces gas mileage and could cause additional tire ware and handling issues.
Those PSI don't apply if you use different tires, and can be dangerous is you downgrade to a D vs. E rated tire. The calculation is pretty simple. Know your max PSI at max weight. Then, determine unloaded weight; then as a % of max weight the tire allows. Then reduce your PSI by that same %.