This 11 speed free hub is only compatible with model-year 2013 (V8) and 2014 (V9) Zipp wheelsets. For more information on identifying hub model years, please see our hub timeline. Check that your hub has a black end cap before using this free hub. Use the spacer for compatibilty with 10 speed Shimano and SRAM drivetrains after installation.The red free hub is designed for SRAM or Shimano® drivetrains and includes a spacer for 10-speed compatibility. (This is NOT a Complete Conversion Kit for 10 Speed Wheels)