I'm seeing lots of false information both on here and on Facebook regarding tire pressures when going to an LT tire from a P metric so i'd figure I'd post this. The answer is definitely NOT the pressure on the placard, you'll kill both your rolling resistance (MPG) and the outside edge of your tires. Toyo made a chart specifically for this, and it's very helpful. Hopefully, we can make this a sticky!
https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf
In short , you need to look at your OEM tire size and pressure on the door, take that number to the chart for the weight (don't think the weight is on the placard). Take that weight to your new tire size and you'll have your PSI. In my example, it was 285/45/22 @ 36 PSI = 2416lbs. I made the switch to a 35x12.50x20, so I take that 2416 to that tire size which takes me to 43ish PSI (right between 40-45). I run the front at 48 being a little heavier, rear at 43. When i am towing, i bump the rear up to 50PSI.
Let's take another example. Another OEM tire size is 275/55/20 @ 35PSI - which is 2603. Say you switch to a 295/60/20 (seems to be a common size guys go to) you'd take 2603lbs to the 295/60/20. That weight falls smack in the middle of 40-45. Since these are trucks and are heavier in the front you need to look at the GAW to figure out the true PSI for the front and rear axle. But, at least these tables give us a starting place.
Hope this is helpful!!
https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf
In short , you need to look at your OEM tire size and pressure on the door, take that number to the chart for the weight (don't think the weight is on the placard). Take that weight to your new tire size and you'll have your PSI. In my example, it was 285/45/22 @ 36 PSI = 2416lbs. I made the switch to a 35x12.50x20, so I take that 2416 to that tire size which takes me to 43ish PSI (right between 40-45). I run the front at 48 being a little heavier, rear at 43. When i am towing, i bump the rear up to 50PSI.
Let's take another example. Another OEM tire size is 275/55/20 @ 35PSI - which is 2603. Say you switch to a 295/60/20 (seems to be a common size guys go to) you'd take 2603lbs to the 295/60/20. That weight falls smack in the middle of 40-45. Since these are trucks and are heavier in the front you need to look at the GAW to figure out the true PSI for the front and rear axle. But, at least these tables give us a starting place.
Hope this is helpful!!