Just switched from a bike with V brakes to one with hydraulic discs, and the pads on the front wheel rub the rotor. The wheel still spins OK, but the sound lets me know I'm losing something in output. I have the pad contact knob turned all the way out. How else can I prevent rub?

From my experience with disk brakes on my dirt bike they always rub. All my bikes have either U-brakes or V-brakes.

First make sure your wheel is on strait! Loosen caliper mounting bolts, squeeze and hold brake lever while retightening mounting bolts. Check for rub. Repeat if necessary