Make your Road Machine or Rock and Roll the most versitile trainer you can find with the addition of a Pro Flywheel. The Pro Flywheel is perfect for hardcore endurance workouts, like tempo and long slow distance rides. Plus, with a cost down time of 60 seconds and a slower accelleration you will notice an increased realism and a more Road Like Feel. 12 lb precision machined metal plate. Mounts to all Kinetic 6.25 lb flywheels: Magnetic, Road and Rock N Roll. Will fit Road and Rock N Roll trainers made after September 2009 serial 76184 and greater.