+1 on weighing.
Go to http://catscale.com
and plug in your zip. It only take a couple of minutes and a few bucks. Do it on the way somewhere; you can hardly avoid the places.
Michelin has load index tables, but I don't think I've seen anything for a 285. BFG doesn't even have them out there. For some reason they're kinda hard to find, but they're basically close to proportional and similar across brands. The tire ass'n publishes some; I used Toyo's at http://toyotires.com/tires-101/tire-loa ... ion-tables
. For my BFGs at 285/75R16 note that the max is 3750 in E range at 80 PSI, so at 50 I can run my just around 5k lb rear end, maybe even 45 per the TRA table.
Or call. I found BFG and Tire Rack would respond to questions once you have your exact weight; they don't seem too keen on just speculating. Getting it right is important.