What is BCD?
BCD is an acronym for Bolt Circle Diameter. It’s the measurement (diameter) of an imaginary circle passing through the centers of all the bolts in a round pattern – like chainring bolts that hold the rings to the crank. On some cranks, like 4 bolt cranks, it’s fairly easy to measure, but for road and cyclocross with 5 bolts, it’s not so easy. Here’s the cheat sheet. More