Engineering a notched belt is a balancing act between flexibility, tensile cord support, and tension distribution. Precisely shaped 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 substances, cover materials, construction methods, tensile cord advancements, and cross-section profiles have led to an often confusing selection of V-belts that are highly 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 possess sidewalls that match corresponding sheave grooves, offering additional surface and greater stability. As belts operate, 
belt pressure applies a wedging force 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 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 share material to provide a layer of safety 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, Electronic) and lengths, and so are widely used to displace V-belts in older, existing applications.
They are accustomed to replace belts on commercial machinery manufactured in other areas of the world.
All the V-belt types noted over are usually available from manufacturers in “notched” or “cogged” variations. Notches reduce bending stress, allowing the belt to wrap V Belt easier around little diameter pulleys and allowing better high temperature dissipation. Excessive high temperature is a major contributor to premature belt failure.
Wrapped belts have a higher resistance to oils and extreme temps. They can be utilized 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 simple pieces of equipment. Just measure the best width and circumference, find another belt with the same sizes, and slap it on the drive. There’s only 1 problem: that approach is about as wrong as you can get.