Full definition
The loaded portion of the belt running from the driver pulley to the driven pulley, carrying the highest tension (T1) during power transmission. The difference between tight-side and slack-side tensions (T1 - T2) is the effective pull that transmits power: P = (T1 - T2) × v, where v is belt speed in m/s. Excessive tight-side tension shortens bearing and belt life; insufficient tension causes slip. The tight side should be on the lower run in horizontal drives so gravity adds to wrap contact. Belt cross-section and cord material must withstand T1 continuously plus peak loads during starts. Per ISO 1081 and Euler belt friction equation. T1 is typically 2-5x the effective pull depending on wrap angle and friction coefficient.