typically on a car with low profile tyres i airdown the rear slightly more, i did this on the 18s i had on my d2 and 17s on the prado, but eventually i jsut started running same pressure front and rear with them with no spun beads. I also run slightly higher pressure when full loaded, some times more in the rear if very heavily loaded over the back axle. The disco's(d2 atleast) alloys have a really tight bead, several tyres places have commented to me how much harder they are to break then other makes. I have been they have an extra ridge or something in the rim to hold the bead.
I have spent alot of time driving at low pressures on the sand with lots of different tyres and have never lost a bead myself, seen it done a few times but its usualy when someone tries going full lock while stationary, i have also seen one pop off a rear on with the car on bad side angle stuck on a dune but that was running very low pressure and being driven stupidly.
