V-belts in classical and single-belt configurations are not optimum from the standpoint of load transfer. Reinforcing cords near the center of the belt sink radially inward under tension, thereby shedding load and reducing the total power capacity of the belt.
Narrow belts overcome this deficiency through a configuration having greater depth to width ratio, which places more of the sheave directly under the reinforcing cord. Thus, loads in the tensile cord are transferred more directly to the sides of the sheave, allowing minimum load shedding and producing better force distributions. For a given width, narrow belts therefore have power ratings much higher than those of conventional V-belts. The improvement in load-carrying capacity becomes more pronounced with increases in the strength of the reinforcing cord.
Narrow belts are standardized, with designations of 3V, 5V, and 8V. Some belts are cogged to maximize the allowable degree of bend, thus permitting operation over small pulleys and allowing space-saving design. These belts represent the highest level of development of V-belts. The space saving they allow is significant, especially in high-reduction drives. In all, they provide the highest power in the smallest package and are particularly well suited to severe-duty applications, including those subjected to shock and high starting loads.