40x13.5 r17 MTRs, Ultra 164 model 17x9 aluminum rims, 6 psi without beadlocks and I never lost a bead.
I ran 6 psi in snow, 12-14 psi in rocks after breaking in the tires by running 10 psi on the road at 55 mph for about 10 miles.

 

Ha ha I have always run 6psi in my 35x1250 without beadlocks. Only once did I pop one off bead... but it also tore a chunk out of the sidewall about 6" wide, so it took alot of force.

 

I have 35x12.50 KM2's on 15x10 aluminums. I run 12-13 on the rocks, and haven't lost a bead yet.

This will have a lot to do with how you drive and what you hit.

 

with my 35x12.5x15 km2's on 15x8 d-windows, I typically rn 8-9 psi. they work so much better than 10+, at 12 they barely flexed.
But I have never lost a bead. I thought i was going to this weekend, I watched the tire fold under its self and the the rim almost touch the ground and it was fine.