For 2006, only the heavier offroad flywheel weight is offered as follows: Fits '03~'05 YZ450F Inertia mass is 6.2kg-cm2 (stock is 3.6kg-cm2) GYT-5TA97-50-50 http://www.yamaha-motor.com/sport/products/modelscitemdetail/5/209/1218/5375/2006/1/4335/0/0/detail.aspx For 2005, the website also acknowledges the lighter flywheel weight: Fits '03~'05 YZ450F Inertia mass is 1.4kg-cm2 heavier than stock (= 5.0kg-cm2). GYT-5TA97-50-00 http://www.yamaha-motor.com/sport/products/modelscitemdetail/5/209/1218/5375/2005/1/5207/0/1/detail.aspx Does anybody know why the lighter GYTR flywheel weight is not offered for 2006 any longer? What is the stock inertia mass on 2006? I want to try a heavier flywheel, but is the offroad weight too heavy for a 45-year-old Sunday motocrosser? Anybody with GYTR flywheel weight experiences please help, thanks.