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The rural roads here can be really rough. I do like 5" as a minimum clearance and I think that's where it was set a few years ago. I just noticed it has dropped some.
I think the rear clearance under the sump was down to about 3" when I hit a manhole cover about six years ago, with unpleasant consequences. That's when I had the rear raised to a bit over 6" (a thinline sump helped, too).
I like the front a bit lower than the rear. An EMPI sway bar is more resilient than a cast aluminum sump.
Besides, it's not necessarily the surface, but what's been deposited upon it that can do you in. A not inconsequential percentage of O'Reilly's inventory ends up gracing our traffic lanes.
Be careful out there, kids.