Engineering a notched belt is definitely a balancing act among versatility, tensile cord support, and stress distribution. Precisely formed and spaced notches help evenly distribute tension forces as the belt bends, thereby assisting 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 methods, tensile cord advancements, and cross-section profiles have led to an often confusing array of V-belts that are extremely application particular and deliver vastly different degrees of performance.
Unlike smooth belts, which rely solely on friction and may track and slide off pulleys, V-belts have sidewalls that match corresponding sheave grooves, providing additional surface and greater stability. As belts operate, belt tension applies a wedging power perpendicular with their tops, pressing 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 into the groove of the sheave while operating under tension impacts its performance.
V-belts are produced from rubber 
or synthetic rubber stocks, so they possess the versatility to bend around the sheaves in drive systems. Fabric materials of various types may cover the share material to provide a layer of protection 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 produced with this profile come in several sizes (A, B, C, D, Electronic) and lengths, and are widely used to replace V-belts in older, existing applications.
They are used to replace belts on industrial machinery manufactured in other parts of the world.
All of the V-belt types noted over are usually available from manufacturers in “notched” or “cogged” V Belt variations. Notches reduce bending tension, allowing the belt to wrap easier around small diameter pulleys and enabling better high temperature dissipation. Excessive warmth is a major contributor to premature belt failure.
Wrapped belts have an increased level of resistance to oils and intense temperatures. They can be used as friction clutches during start up.
Raw edge type v-belts are more efficient, generate less heat, allow for smaller pulley diameters, increase power ratings, and provide longer life.
V-belts look like relatively benign and basic pieces of equipment. Just measure the top width and circumference, find another belt with the same sizes, and slap it on the drive. There’s only one problem: that approach is approximately as wrong as you can get.