Yamaha YXZ1000R Hess Motorsports performance flywheel. 

• CNC Machined Steel and Zinc Plated.
• Installs in about 20 minutes
• Smooths out the power for a more drivable power.
• Makes Stalling much harder
• Transfers power to the ground increasing drive out of the corner
• Works with all engine mods and clutch types
• Made in USA

The heavy weights really help with slow speed drive-ability (Rocks,hills and tight trails) while the light weight helps in build fast rpm in higher speed riding (Dunes, Drag Racing, Short Course).