The wheels need to be off the ground because the torsion bars are under "torsion" when the vehicle is on the ground. The torsion bars are your springs. They can only be adjusted when there is no torsion on them.

96 T100 4x4 - 35's, 4" SL, 2" BL, 4.88s, ARBs, custom bumper & E9000 winch, etc.
99 F-350 4x4 superduty supercab turbodiesel longbed