Spec Clutch SF15S Billet Steel Flywheel SFI Certified

The Spec Clutch SF15S is a high-performance billet steel flywheel CNC-machined to an industry-leading .001 tolerance — ten times tighter than the industry-standard .010. This exceptional precision guarantees a perfectly flat seating surface for the clutch disc and true rotational balance, eliminating dimensional runout that can cause damaging vibrations and rob engine power. Every Spec steel flywheel carries SFI certification, making it suitable for competitive and high-rpm racing environments.

Key Features:

• CNC-machined from high-carbon billet steel to a precise .001 tolerance
• SFI certified for safety in competitive racing applications
• Perfectly flat clutch disc bedding surface for consistent friction and engagement
• Replaceable steel friction plate formulated for optimum clutch bedding and holding power
• Rebuildable design for long-term serviceability
• Engineered for optimized Moment of Inertia (MOI) to maximize performance
• Made in the U.S.A.

The flywheel plays a critical role in clutch performance and drivetrain efficiency. It must deliver a consistent friction surface for the clutch disc, provide the correct rotational inertia for the application, and maintain true balance at high rpm. Spec engineers invest significant research and development into optimizing flywheel dimensions and weight for a wide range of performance driving and racing disciplines. Steel flywheels offer a medium-weight inertia profile that tends to be more street-friendly, retaining more rpm between shifts for smoother drivability compared to lighter aluminum alternatives.

The SF15S is part of Spec's lineup of billet flywheels developed and tuned for specific driving environments, offering a performance upgrade that works seamlessly with Spec clutch kits across their Stage 1 through Stage 5 range.