Impressive efficiency combined with excellent reliability, perfect for a demanding commuter or cycle tourist . 72% efficiency at 10 mph . 6-volt 3-watt output. Ideal wheel diameter: 26" wheels and larger. Rim brakeItem Specifications: Number of Holes: 32, Front or Rear?: Front, Color: Silver, Model Name: Dynacoil, Rear Axle Spacing: QRx100, Spoke: J-Bend, Brake Type: Rim, Weight: 420g,