Proper Tire Inflation

First time posting on this site since I joined the Taco family. I bought a used '16 TRD OR a couple months ago with a lift as well as aftermarket rims and tires. LOVE the truck. Small problem: I'm not sure what pressure to inflate the tires to. The tires are Nitto Terragrappler G2's (size LT285/65R18). Sidewall says max load is 3640lbs @ 80psi but i'm not sure how to use this info to determine what pressure I need. Explanation of how to calculate is best, but link to an online calculator is also great. Thanks!!

P.S. Here's some pics of my new Taco

 

The only way to the the proper PSI for your specific truck is th chalk test! Google will help you out on that one

 

Do the chalk test. On my mostly stock truck, with lift and 265/75-16 E-Rated tires, my results put me at 29/30 psi - right in line with the door sticker.

dp

 

Chalk test it is! Thanks!