Engineering a notched belt is definitely a balancing act among versatility, tensile cord support, and tension distribution. Precisely formed and spaced notches help to evenly distribute stress 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 resulted in an often confusing selection 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 slip off pulleys, V-belts have sidewalls that fit into corresponding sheave grooves, offering additional surface and greater balance. As belts operate, belt stress applies a wedging pressure perpendicular with their tops, pushing their sidewalls against the sides of the sheave grooves, which multiplies frictional forces that allow the drive to transmit higher loads. What sort of V-belt fits in to 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 types may cover the share material to provide a layer of security and reinforcement.
V-belts are manufactured in various 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 displace V-belts in old, existing applications.
They are used to 
replace belts on industrial machinery manufactured in other areas of the world.
All 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 high temperature dissipation. Excessive temperature is a major contributor to premature belt failure.
Wrapped belts have an increased level of resistance to oils and severe temps. 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 best width and circumference, discover another belt with the same dimensions, and slap it on the drive. There’s only one problem: that V Belt strategy is about as wrong as possible get.