The ACT 4-Puck Solid Hub Race Disc is legal for all forms of racing that require SFI compliance. The biggest benefit of the ACT 4-Puck Solid Hub Race Disc is its extremely fast shifts thanks, in part, to its reduced inertia. An ACT R4 race disc friction surface has good durablity but will have shortened spline life. ACT designed the R4 for a heavily modified drag race or road race cars where extremely harsh engagement and clutch chatter is expected.