Engineering a notched belt is certainly a balancing act between flexibility, tensile cord support, and tension distribution. Precisely formed and spaced notches help evenly distribute tension forces as the belt bends, thereby helping to prevent undercord cracking and extending belt life.
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 particular and deliver vastly different levels of performance.
Unlike toned belts, which rely solely on friction and can track and slide off pulleys, V-belts possess sidewalls that match corresponding sheave grooves, offering additional surface area and greater stability. 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 made from rubber or synthetic rubber stocks, so they have 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 various industry standard cross-sections, or profiles
The v belt china classical V-belt profile goes back to industry standards developed in the 1930s. Belts manufactured with this profile can be found in many sizes (A, B, C, D, E) and lengths, and are widely used to replace V-belts in old, 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 above are typically available from manufacturers in “notched” or “cogged” versions. Notches reduce bending tension, allowing the belt to wrap more easily around small diameter pulleys and permitting better temperature dissipation. Excessive heat is a major contributor to premature belt failing.
Wrapped belts have an increased level of resistance to oils and extreme 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, boost power ratings, and offer longer life.
V-belts appear to be relatively benign and basic pieces of equipment. Just measure the top width and circumference, find another belt with the same measurements, and slap it on the drive. There’s only 1 problem: that strategy is approximately as wrong as possible get.