Gear Calculator Top Sprocket: Bottom Sprocket: Tach RPM: Number Of Driver Teeth: Track Pitch: Clutch Ratio: When it is Non-Overdrive use 1.00 If Overdrive Ski Doo use .85 For Overdrive Yamaha, Cat, or Polaris use .90 Clutch Gear Reduction: If the RX-1 use 1.1935 For the EFI Genesis Engines, use 1.2333 All others use 1.00 Calculate MPH: