Engineering a notched belt is usually a balancing act among versatility, tensile cord support, and stress distribution. Precisely designed and spaced notches help to evenly distribute tension forces as the belt bends, thereby helping to prevent undercord cracking and extending belt existence.
Like their synchronous belt cousins, V-belts have undergone V Belt 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 specific and deliver vastly different degrees of performance.
Unlike toned belts, which rely solely on friction and will track and slide off pulleys, V-belts have sidewalls that match corresponding sheave grooves, providing additional surface and greater balance. As belts operate, belt pressure applies a wedging drive perpendicular with 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 in to the groove of the sheave while working under pressure impacts its performance.
V-belts are made from rubber or synthetic rubber stocks, so they possess the flexibility to bend around the sheaves in drive systems. Fabric materials of various types 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 goes back to industry standards created in the 1930s. Belts produced with this profile can be found in many sizes (A, B, C, D, E) and lengths, and so are widely used to replace V-belts in older, existing applications.
They are used to replace belts on commercial machinery manufactured in other areas of the world.
All the V-belt types noted above are typically available from manufacturers in “notched” or “cogged” variations. Notches reduce bending tension, allowing the belt to wrap more easily around little diameter pulleys and allowing better temperature dissipation. Excessive warmth is a major contributor to premature belt failing.
Wrapped belts have a higher level of resistance to oils and severe temperatures. They can be used 
as friction clutches during set up.
Raw edge type v-belts are more efficient, generate less heat, enable smaller pulley diameters, boost power ratings, and provide longer life.
V-belts appear to be 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 1 problem: that approach is approximately as wrong as you can get.