Kinetic Pro FlywheelThe Pro Flywheel features two separate flywheel options - an attached 6 lb flywheel which has been designed for interval training, plus an additional 12 lb flywheel (18 lbs total) for hard-core endurance workouts, like tempo and Long Slow Distance rides.Please note: If you'd like the option to use our 12 lb Pro Flywheel and you own an older trainer with a serial number lower than 76184, you can upgrade your Road Machine, Cyclone, or Rock and Roll Road by purchasing a Pro Resistance Unit.