How to Know the BCD (Bolt Circle Diameter) of Your Chainrings?
The BCD (Bolt Circle Diameter) is the diameterof a circle passing through the center of all chain rings bolts holes.
It's one of the most important information to know if a chain rings fit on a crank set or not.
5 Arms Chainrings
On a 5 arms chain rings, you have to measure the distance between two neighbor bolt holes from center to center.
Use the measurement to find your BCD on the table below:
| 34.1 mm |  | 58 mm |
| 43.5 mm | | 74 mm |
| 50.6 mm | | 86 mm |
| 55.3 mm | | 94 mm |
| 64.7 mm | | 110 mm |
| 71.7 mm | | 122 mm |
| 76.5 mm | | 130 mm |
| 79.4 mm | | 135 mm |
| 84.7 mm | | 144 mm |
4 Arms Chainrings
On a 4 arms chain rings, you have to measure the distance between twoopposite bolt holes from center to center.
| 64 mm | | 64 mm |
| 76 mm | | 76 mm |
| 80 mm | | 80 mm |
| 94 mm | | 94 mm |
| 102 mm | | 102 mm |
| 104 mm | | 104 mm |
| 120 mm | | 120 mm |
| 146 mm | | 146 mm |
Please note: Shimano Dura-ace FC-9000 / Ultegra FC-6800 / 105 FC-5800 & SRAM XX1 cannot be measured like this because of the asymmetrical placement of bolt holes.