RISK RA133 Bicycle Headset Crown Race Adapter, Tapered to Straight Fork Compatible, 45° Split Design

The RISK RA133 Crown Race Adapter is a headset base ring designed for bicycle forks, compatible with both tapered (1.5″ / 39.8mm) and straight (28.6mm) steerer tubes. Made from precision CNC-machined aluminum alloy, this crown race features a 45° split-open design, allowing tool-free installation without removing the fork.

Available in two versions — C base (for 1.5″ tapered forks) and D base (for straight or tapered forks with included adapter insert) — this part is compatible with external, integrated, and large-diameter 55/56mm headset bearing systems.

Key Benefits

• Universal Fork Compatibility
  C base fits 1.5″ (39.8mm) tapered forks; D base fits both 28.6mm straight forks and 1.5″ tapered forks (includes C base function).
• Split-Open Design for Easy Installation
  45° open-cut structure allows tool-free hand installation without disassembling the fork.
• CNC Precision Machined
  Made from high-quality aluminum alloy for a tight, secure fit and long-lasting durability.
• Convertible Insert System
  D base can be converted to C base using the included adapter insert, offering flexible use between straight and tapered steerer tubes.
• Wide Headset Compatibility
  Suitable for external, semi-integrated, and fully integrated headsets with 52mm bearing OD, including 44mm external, 44–50.6mm external, 42–52mm integrated, 44–56mm setups, and more.

Suitable For

This crown race adapter is suitable for:

• Mountain bikes (MTB)
• Road bikes
• Bicycles with 1.5″ tapered fork steerer tubes
• Bicycles with 28.6mm straight fork steerer tubes
• External, semi-integrated, or integrated headset systems
• 52mm OD bearing headsets
• Headset upgrade or replacement projects

Notes

• Please confirm your fork steerer tube type (straight or tapered) and headset bearing size before purchase.
• C base and D base serve different steerer tube types — check compatibility carefully.
• Manual measurement may have slight tolerance; please refer to actual product for reference.
• Bearing and fork shown in images are for demonstration only and are not included.

Product Details

Package Includes

• 1 × RISK RA133 Crown Race (C base or D base, per selection)
• 1 × Adapter Insert (included with D base for tapered/straight conversion)