Ok here are a selection of the tables that are pertinent to load/inflation of stock disco to LT245, LT265, and LT285. This is a little more general table than I've had in the past (the pressure increments are much wider on this table) unfortunately I don't have that book here and no longer work full time at the tire shop I used to run.
The method with these tables is:
1. determine stock size (and in this instance load index #)
2. determine cold tire inflation front and rear of stock size
3. refer to stock size in load/inflation table (in this instance determined by load index #) to find load (stock) at pressure (stock)
4. refer to LT Metric load/inflation table for tire size in question
5. match stock load front and rear with the LT load (also front/rear)
6. apply tire pressures as indicated
RULE of THUMB:
Now, I haven't gone over the numbers in this set of tables to be sure but sometimes a tire carries the same load or a greater load at less than the stock tire pressure. The rule of thumb is NEVER INFLATE A PLUS SIZE TIRE TO LESS THAN THE ORIGINAL (STOCK) TIRE PRESSURE FOR ROAD TRAVEL.
**disclaimer** I know there are a ton of people who run a low tire pressure in oversized tires and have never had a problem. I also know a lot of skiptards who have had tire failure, loss of control, etc. This is the way I learned it at every Michelin/BFG/Bridgestone seminar i've ever attended. The main cause of tire failure is due to underinflation/overloading...in fact its printed on most tires sold in north america.
http://picasaweb.google.com/clarkwjackson/LoadAndInflationTables?feat=directlink
edit. sorry it took me so long to get this stuff posted, we just had our first baby a week ago monday, so I've been a little preocupied.