Engineering a notched belt is 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 assisting 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 led to an often confusing selection of V-belts that are extremely application specific and deliver vastly different levels of performance.
Unlike smooth belts, which rely solely on v belt china friction and will track and slip off pulleys, V-belts possess sidewalls that fit into corresponding sheave grooves, offering additional surface area and greater balance. As belts operate, belt stress applies a wedging drive perpendicular to 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 manufactured from rubber or synthetic rubber stocks, so they possess the flexibility to bend around the sheaves in drive systems. Fabric materials of various kinds may cover the stock material to supply a layer of security and reinforcement.
V-belts are manufactured in various industry standard cross-sections, or profiles
The classical V-belt profile dates back to industry standards developed in the 1930s. Belts produced with this profile can be found in a number of 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 usually available from producers in “notched” or “cogged” versions. Notches reduce bending stress, allowing the belt to wrap easier around small diameter pulleys and enabling better temperature dissipation. Excessive warmth is a major contributor to premature belt failing.
Wrapped belts have an increased resistance to oils and extreme temps. They can be used as friction clutches during set up.
Raw edge type v-belts are better, generate less heat, enable smaller pulley diameters, enhance power ratings, and provide longer life.
V-belts look like relatively benign and basic devices. 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 about as wrong as you can get.