Full definition
The ratio of useful output power to input power in a mechanical system, expressed as a percentage: η = (Pout/Pin) × 100%. Losses are dissipated as heat through friction, hysteresis, windage, and churning. Typical efficiencies by drive type: V-belts 93-98%, timing belts 97-99%, flat belts 98-99%, roller chains 95-98%, spur/helical gears 96-99% per stage, bevel gears 95-98%, worm gears 45-90% (highly ratio-dependent), planetary gears 95-97%. For multi-stage systems, multiply individual efficiencies: a V-belt (95%) driving a worm reducer (70%) yields 66.5% total. Efficiency decreases with wear, misalignment, improper lubrication, and overload. Per ISO 14179 for gears. Higher efficiency means less energy cost, less heat generation, and smaller cooling requirements.