tire psi for 285's and 18's

Use the Chalk method to determin the psi for your tires. Pressure varies truck to truck, as some weight more than others, due to the way they are outfitted, or whatever.

 

CHECKING TIRE FOOTPRINT WITH A CHALK LINE

Park on level ground and aim front tires straight ahead. Draw a line completely across the tread.
Pull ahead 2-3 tire revolutions or until the chalk starts wearing off.
If the chalk mark is worn off equally across the width of the tread, the inflation pressure is correct.

If the chalk mark is worn off more in the center than at the edges, as shown here, the tire is over inflated.
If the chalk mark is worn off more at the edges than in the center, as shown here, the tire is under inflated.