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.
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.
This crown race adapter is suitable for:
| Item | Specification |
|---|---|
| Brand | RISK |
| Model / Part Number | RA133 |
| Product Name | Crown Race Adapter |
| Material | Aluminum Alloy (CNC Machined) |
| Design | 45° Split-Open Structure |
| Compatible Fork Type | Tapered (39.8mm/1.5") & Straight (28.6mm/1.125") |
| C Base Thickness | 5mm |
| C Base Inner Diameter | Approx. 39.7mm |
| C Base Outer Diameter | Approx. 51mm |
| C Base Weight | Approx. 6g |
| D Base Thickness | 5mm |
| D Base Inner Diameter | Approx. 29.9mm |
| D Base Outer Diameter | Approx. 51mm |
| D Base Weight | Approx. 12.6g |
| Compatible Bearing OD | 52mm |
| Package Weight | Approx. 13g |
