The reduced inertia of the ACT 6-Puck Solid hub allows for very fast shifts at the expense drivability. An ACT R6 race disc friction surface has very good durability but will have shortened spline life. ACT designed the R6 for a highly modified track cars where harsher engagement is expected and some clutch chatter is not a problem. The 6-puck layout of the R6 will absorb, and dissipate, more heat than a 4-puck unit. The ACT 6-Puck Solid Hub Race Disc is legal for all forms of racing that require SFI compliance.