Full definition
The arc of the pulley circumference in direct contact with the transmission belt, measured in degrees (°). It determines traction capacity: a greater angle means higher power transmission capability. The minimum recommended value is 120° per ISO 1081; below this, excessive slippage and premature wear occur. Calculated as θ = 180° − 2·arcsin((D−d)/(2C)), where D and d are pulley diameters and C is center distance. Increase it with an idler pulley or by extending center distance. Each 10° reduction below 180° decreases capacity by approximately 3-5%.