Supply Chain Automation Equipment Maintenance Practice Test

The belt drive ratio is determined by the sizes of the pulleys at the belt’s pitch line. The pitch diameter is the important dimension because the belt engages along the pitch circle, not the outer edge. Since the belt’s linear speed is the same around the belt, the relationship between the pulley speeds comes from equating belt speed on both pulleys: the drive pulley speed times its pitch diameter equals the driven pulley speed times its pitch diameter. In symbols, ω_drive × (Dp_drive/2) = ω_driven × (Dp_driven/2), so the speed relationship is ω_driven/ω_drive = Dp_drive / Dp_driven. In many contexts this ratio is expressed as the driven-to-drive pitch-diameter ratio, which is why the ratio is given by driven pitch diameter divided by drive pitch diameter. This is why pitch diameters, not outer diameters or belt length, determine the belt drive ratio.