Improved technologies are needed to make polycrystalline-diamond-compact (PDC) bits effective in directional- and horizontal-drilling programs. The dual-torque concept (DTC) establishes an effective method for PDC-bit development for directional and horizontal drilling. The DTC redefines the torque/weight-on-bit (WOB) relationship of PDC bits. It combines the torque requirements of sliding and rotating modes into a single curve characterized by sliding slope, rotating slope, and transitional WOB.