AHC with non-AHC rear springs and body armor
I’m a big fan of the AHC suspension that comes stock on the LX. It’s been working great even after installing on MetalTech sliders. However, after adding the Bump It Offroad rear bumper, the AHC didn’t work so well. The Cruiser could barely stay in the AHC “Normal” height position, often dropping down to “Low” mode. It’s only after I removed the 3rd row seats and spare tire could the AHC stay in Normal height. And forget about even trying to go into High mode, it wasn’t happening.
Here are the AHC ratings from Lexus:
"Height cannot be raised if the load exceeds the following limits:
Up to 4 occupants plus 661 lbs in NORMAL mode (1261 lbs)
Up to 4 occupants plus 375 lbs in the HIGH mode (975 lbs)
If the above load capacity is exceeded, the desired vehicle height may not be obtained even if the height select switch is pushed. (If the vehicle height cannot be raised in the normal mode and the height control indicator indicates “LO”, this is because the vehicle is loaded too heavily."
Not ready to give up on the AHC, I decided to give it some better reinforcement - enter
Toyota Land Cruiser non-AHC rear springs. Toyota part# 48231-6A690 (driver-side), # 48231-6A680 (passenger).
The 100 series non-AHC springs are designed to carry a much heavier load since there is no AHC to supplement it. So my non-scientific hypothesis was that the higher spring rating would be enough to support the additional weight of the rear bumper with AHC.

After installation, the hypothesis proved to be true. In fact, it can support significantly more weight than just the bumper. There is a trade-off with the ride quality though.
After installing the rear springs, the LX had a much bouncier ride. The springs did settle after a couple of weeks and even more so in the last 8 months. But the ride has definitely lost some of its butter smooth Lexus qualities.

It’s a stiff, firm ride out back, but the more weight you throw in the back, the more it rides like a Lexus. Just this past week I had over 900lbs of passengers, including 400lbs specifically in the 3rd row. I tested the AHC and was able to get into High mode! The overall drive was very compliant and never felt overloaded.
The photos from my post above with the Bump It Offroad bumper are with the non-AHC springs installed. And finally, I was able to test out this entire setup in Moab.
Where the rubber meets the off-road!