I often wondered where it being a good idea came from. That to me is why I know the inertia factor might play a roll, but a 5k to 7 k launch with one bites just the same and the big difference is turbo spool and effortless speed shifting. The concept behind a lightweight flywheel stems from the desire to enhance low-rpm throttle response on high RPM horsepower applications. With the lightened flywheel in Twin and Triple Plate Clutch kits, a quick rise in RPM can be attained from light throttle input for easier RPM matching when shifting and to counter low torque at low RPM levels. Some are made of chrome-moly , some Carbon steel, chrome moly steel forgings and Billet Chrome-Moly Steel.
HKS has them for all kits OS Giken has them for all kits Nismo RPS ATS Exedy Tilton and so on.