Full definition
The pulley connected to the motor or prime mover (power source), transmitting power to the belt. In a speed-reduction drive, the driver pulley is the smaller pulley, rotating at motor speed. Its diameter determines belt speed: v = π × Dp × RPM / 60,000 (m/s). Because it is smaller, it typically has the smaller wrap angle, making it the limiting factor for traction capacity — this is why increasing wrap angle on the driver pulley (via idler or longer center distance) is most effective. The driver pulley must respect minimum diameter limits per belt profile to avoid excessive flex fatigue: SPA min 90 mm, SPB min 140 mm, SPC min 224 mm, A min 75 mm, B min 125 mm, C min 200 mm. Material and construction must handle motor starting torque (150-300% of rated). Per ISO 4183 and manufacturer minimums.