20s for the Demon - how low can I go? (big wheel haters don't look)

Asking for advice on that endeavor is kinda a waste of time really. With all that diameter your suspension is gonna have all the ground clearance in the world. I would allow 2 inches of up travel for the tire as a minimum. Its up to you where you end up since nobody has really went that route that I know of. You could always tub it clear to the trunk filler panel though if ya want.