The general rule for deflating has to do with two things: 1. Any ".5" tire; i.e. 16.5 or 19.5 has very little sidewall and the wheels lacks a safety bead to keep it on the rim at lower pressure.
so the only way a, .5 tire/wheel would work at low pressure is to use beadlocks. However, lowering the pressure is not recommended by experienced ".5" manufacturers.
2. Lowering the pressure has to do with the height of the sidewall on normal, non, ".5" tires. A tire like the G2 275x55R20 has a lot of wheel and a rather short sidewall and not expected to have much air reduction before any danger is reached. This means: don't lower the pressure unless you absolutely have to get out of trouble. We have a 2011 Grand Chero Limited with 18 inch wheels and enough sidewall to deflate a ways. Of all the possibilities in wheel tire combo for a JGChero, i like our 18's the best, as a wide variety of capacities can be had; a higher capacity than 15, 16, 17. 19, or 20 inch tires that fit a JGChero.
We had good luck with Cooper Discoverer AT-3's with long life and pretty good on snow and ice with big tread blocks, sipes, and tiny voids. They don't look as Macho as mud tires but are quieter and last longer.
The newest version seems to be the best of the AT-3's as they eliminated the crescendo of noise toward the end of tread life.
Since I do a lot of sand and dune running with my 10K pound truck camper, I elected to keep the 16 inch wheels and mount 35 inch tires which give me plenty of sidewall with which to deflate down to about 20 pounds when needed.
