http://www.zr1netregistry.com/ZR1_tr...g.htm#Flywheel
and
http://www.zr1specialist.com/HAT%20W...eel-clutch.htm
Your choice is either stock or light weight. The main complaint with the light weight is gear rattle. Some don't mind, and others can't stand it. I think with a sprung hub and upgrading the oil to the synthetic BMW stuff is supposed to help.