How to measure chainring Bolt Circle Diameter (BCD).

To choose the correct chainring, 1) determine the number of teeth (they're usually marked, or simply count them), 2) determine how many bolt holes there are (usually 4 or 5), and 3) determine the Bolt Circle Diameter (BCD; see diagram).

Common BCDs include:
130mm (Shimano Road)
135mm (Campagnolo Road)
110mm (Compact Road)
and
104mm, 94mm, and 64mm (Mountain)

Finding the number of teeth and bolts holes is easy. If you don't know your chainring's BCD, measuring it is tricky. So, instead, measure the exact distance (center to center) between 2 adjacent bolt holes. Then find that number on the correct chart below to determine the BCD for your chainring.

BCD Chart for 5-bolt Chainrings
Bolt to Bolt (measure center to center) Bolt Circle Diameter (BCD)
32.9mm 56mm
34.3mm 58mm
43.5mm 74mm
55.4mm 94mm
64.7mm 110mm
76.4mm 130mm
79.5mm 135mm
84.6mm 144mm
BCD Chart for 4-bolt Chainring
Bolt to Bolt (measure center to center)
Bolt Circle Diameter (BCD)
41mm 58mm
45.3mm 64mm
48.1mm 68mm
73.6mm 104mm
79.2mm 112mm

If you have any questions concerning chainring compatibility, please contact us.