ACT brand pressure plates are the ONLY legal high performance clutches allowed in Spec Miata per the rules. Matching the disc with the pressure plate is important. Clamping force, spring pressure, friction material all must work together to form the best clutch package.
The unsprung hub is lighter and offers a small performance advantage. In fact the ACT four puck clutch is lighter then most other manufactures of three puck clutch disc.
For drivers with poor shifting techniques or who are regularly hurting transmissions/differentials, we recommend the sprung hub.