Engineering a notched belt is usually a balancing act among versatility, tensile cord support, and stress distribution. Precisely designed and spaced notches help evenly distribute tension forces as the belt bends, thereby helping to prevent undercord cracking and extending belt lifestyle.
Like their synchronous belt cousins, V-belts have undergone tremendous technological development since their invention by John Gates in 1917. New synthetic rubber compounds, cover materials, construction strategies, tensile cord advancements, and cross-section profiles have resulted in an often confusing selection of V-belts that are highly application specific and deliver vastly different degrees of performance.
Unlike flat belts, which rely solely on friction and will track and slip off pulleys, V-belts possess sidewalls that fit into corresponding sheave grooves, providing additional surface and greater balance. As belts operate, belt pressure applies a wedging pressure perpendicular to their tops, pushing their sidewalls against the sides of the sheave grooves, which multiplies frictional forces that allow the drive to transmit higher loads. How a V-belt fits in to the groove of the sheave while working under stress impacts its performance.
V-belts are manufactured from rubber or synthetic rubber stocks, so they have the versatility to bend around the sheaves in drive systems. Fabric V Belt materials of various kinds may cover the stock material to provide a layer of safety and reinforcement.
V-belts are manufactured in various industry regular cross-sections, or profiles
The classical V-belt profile dates back to industry standards developed in the 1930s. Belts manufactured with this profile come in several sizes (A, B, C, D, E) and lengths, and are widely used to displace V-belts in older, existing applications.
They are used to replace belts on commercial machinery manufactured in other areas of the world.
All of the V-belt types noted over are usually available from manufacturers in “notched” or “cogged” variations. Notches reduce bending stress, enabling the belt to wrap easier around small diameter pulleys and allowing better heat dissipation. Excessive heat is a major contributor to premature belt failure.
Wrapped belts have a higher resistance to oils and intense temps. They can be utilized as friction clutches during start up.
Raw edge type v-belts are more efficient, generate less heat, allow for smaller pulley diameters, enhance power ratings, and provide longer life.
V-belts look like relatively benign and simple pieces of equipment. Just measure the best width and circumference, find another belt with the same measurements, and slap it on the drive. There’s only one problem: that strategy is approximately as wrong as 
you can get.