Engineering a notched belt is usually a balancing act among flexibility, tensile cord support, and tension distribution. Precisely designed and spaced notches help to evenly distribute stress forces as the belt bends, thereby helping to prevent undercord cracking and extending belt existence.
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 led to an often confusing selection of V-belts that are extremely application particular and deliver vastly different levels of performance.
Unlike smooth belts, which rely solely on friction and will track and slide off pulleys, V-belts have sidewalls that fit into corresponding sheave grooves, providing additional surface and greater stability. As belts operate, belt tension applies a wedging force perpendicular to their tops, pressing their sidewalls against the sides of the sheave grooves, which multiplies frictional forces that permit the drive to transmit higher loads. How a V-belt fits into the groove of the sheave while operating under stress impacts its performance.
V-belts are produced from rubber or synthetic rubber stocks, so they have the flexibility to bend around the sheaves in drive systems. Fabric materials of varied kinds may cover the stock material to supply a layer of safety and reinforcement.
V-belts are manufactured in a variety of industry standard cross-sections, or profiles
The classical V-belt profile dates back to industry standards developed in the 1930s. Belts manufactured with this profile can be found in many sizes (A, B, C, D, V Belt Electronic) and lengths, and so 
are widely used to displace V-belts in old, 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 above are usually available from producers in “notched” or “cogged” versions. Notches reduce bending tension, allowing the belt to wrap more easily around little diameter pulleys and allowing better warmth dissipation. Excessive warmth is a significant contributor to premature belt failure.
Wrapped belts have a higher level of resistance to oils and severe temperatures. They can be used as friction clutches during start up.
Raw edge type v-belts are better, generate less heat, allow for smaller pulley diameters, enhance power ratings, and offer longer life.
V-belts appear to be relatively benign and simple pieces of equipment. Just measure the best width and circumference, discover another belt with the same sizes, and slap it on the drive. There’s only one problem: that approach is about as wrong as you can get.