Reports of the demise of this Web site are greatly exaggerated! We at sheldonbrown.com thank Harris Cyclery for its support over the years. Harris Cyclery has closed, but we keep going. Keep visiting the site for new and updated articles, and news about possible new affilations.


Measuring Bicycle Crank/Chainring Bolt Circle Diameter

by Sheldon Brown
revised and updated by John Allen

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Use this page in connection with our bolt-circle diameter cribsheet, which identifies the major brands and models associate with each bolt-circle pattern

No two of an odd number of bolt holes are directly opposite another. Also, a protruding part may prevent direct measurement of the bolt-circle diameter of a crank spider. So, the cribsheet lists spacings between bolt holes which are not opposite one another. These can be measured with a ruler or caliper. The table at the bottom of this page gives the bolt-circle diameters that correspond to the measurements.

Many references describe distances between bolt holes as "center to center," but there is only empty space at the center of a hole! D'oh! Measuring from right side to right side or left side to left side is more reliable -- as shown in the photo below.

Measuring between two adjacent bolt holes

Measuring between non-adjacent holes reduces the likelihood of mistakes when differences are small. As an exercise, you may check the dimensions in the table on our cribsheet page to identify the chainring in these photos, and then double-check against the brand-name stamp on the chainring.

Measuring between non-adjacent bolt holes

Some newer chainrings have unevenly-spaced holes. You need to measure between more than one pair of holes to identify these. Details are on another page.

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Reports of the demise of this Web site are greatly exaggerated! We at sheldonbrown.com thank Harris Cyclery for its support over the years. Harris Cyclery has closed, but we keep going. Keep visiting the site for new and updated articles, and news about possible new affilations.

Copyright © 2005 Sheldon Brown

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Last Updated: by John Allen