It's interesting you mention rolling resistance because in mountain biking, cross country anyway, where there will be climbing on loose surfaces, you have to tr

It's interesting you mention rolling resistance because in mountain biking, cross country anyway, where there will be climbing on loose surfaces, you have to trade off rolling resistance of the rear tire against traction. If you over-inflate your tires, you'll have less traction. There's also the fact that during a tough climb on a trail with obstacles (roots rocks) you can't just power your way up, you have to maintain constant awareness of where the contact patch of your rear wheel is at all times, and modulate the power such that you deliver the most power where you have the most traction. Fail to do that on a rock or root and you'll blow the climb.