Originally Posted by
Wingsprint
Is seems counter-intuitive, but lower pressures on a mountain bike will effetely decrease rolling resistance on uneven surfaces. This is because instead of bouncing off and up small rocks, roots, etc., the lower pressure allows the tire to simply absorb and roll over.
Someone posted a link before, but I cannot find it now, to a study that showed where on rough off trails the overall rolling resistance is improved along with traction at lower pressures. Pretty much opposite of hard pack trails and pavement.