Engineering a notched belt is usually a balancing act between versatility, tensile cord support, and stress distribution. Precisely designed and spaced notches help to evenly distribute stress 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 strategies, tensile cord advancements, and cross-section profiles have led to an often confusing selection of V-belts that are highly application specific and deliver vastly different levels of performance.
Unlike flat belts, which rely solely on friction and may track and 
slip off pulleys, V-belts have sidewalls that match corresponding sheave grooves, providing additional surface and greater V Belt stability. As belts operate, belt tension applies a wedging push 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 in to the groove of the sheave while working under tension impacts its performance.
V-belts are manufactured from rubber or synthetic rubber stocks, so they possess the versatility to bend around the sheaves in drive systems. Fabric materials of varied kinds may cover the stock material to provide a layer of protection 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 come in several sizes (A, B, C, D, E) and lengths, and are widely used to replace V-belts in older, existing applications.
They are accustomed to replace belts on industrial machinery manufactured in other areas of the world.
All the V-belt types noted above are typically available from producers in “notched” or “cogged” versions. Notches reduce bending stress, permitting the belt to wrap easier around small diameter pulleys and allowing better heat dissipation. Excessive heat is a significant contributor to premature belt failing.
Wrapped belts have an increased level of resistance to oils and severe 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 simple devices. Just measure the best width and circumference, discover 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.