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:

Stronglight BCD Calculation
34.1 mmarrow right58 mm
43.5 mmarrow right74 mm
50.6 mmarrow right86 mm
55.3 mmarrow right94 mm
64.7 mmarrow right110 mm
71.7 mmarrow right122 mm
76.5 mmarrow right130 mm
79.4 mmarrow right135 mm
84.7 mmarrow right144 mm

4 Arms Chainrings

On a 4 arms chain rings, you have to measure the distance between twoopposite bolt holes from center to center.

Stronglight BCD Calculation
64 mmarrow right64 mm
76 mmarrow right76 mm
80 mmarrow right80 mm
94 mmarrow right94 mm
102 mmarrow right102 mm
104 mmarrow right104 mm
120 mmarrow right120 mm
146 mmarrow right146 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.