What does ‘pcd’ or ‘bcd’ mean?


Pitch circle diameter (pcd) or bolt circle diameter (bcd) refer to the diameter of the imaginary circle which passes through the centre of the bolts or bolt holes on your chain ring/crank arm (or wheel bolts of you’re looking at a car wheel).

For a 4 bolt crank simply measure the distance between 2 opposite bolt holes (as above).

If you’ve got a 5 bolt crank (these tend to be used on road or cyclocross bikes) you can work it out by following the principle above, use one of the various pcd/bcd online calculators or, as bike cranks are well standardised these days, you can look up the measurements on manufacturer or independent bike websites.  If you’re keeping an old bike running Sheldon Brown has a comprehensive crib sheet available.


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