If no one else has said it...
Weigh the rig, all four corners separately. Weigh the rig in total as well.
Look up the tires you have on the rig on the manufacturer;s website. Get the EXACT tire, do not assume that yours is like the one listed above or below where you think yours should be, If they aren't listed, get the manufacturer's tech people on the phone. inflate the tire to the suggested PSI for the load you are placing on the tire. If the tire is rated for less than what you have weighed in at, you need to STOP and REPLACE your tires, DO NOT PASS GO! You are looking for a major hurt to your rig and potentially your physical well being.