{"id":62301,"date":"2024-04-24T13:00:00","date_gmt":"2024-04-24T11:00:00","guid":{"rendered":"http:\/\/8f65ec3c-16c1-4137-af41-7b3ff0680694"},"modified":"2024-04-24T13:59:50","modified_gmt":"2024-04-24T11:59:50","slug":"how-to-measure-bcd-and-common-chainring-sizes-explained","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/cyclingplus\/rss_feed\/how-to-measure-bcd-and-common-chainring-sizes-explained\/","title":{"rendered":"How to measure BCD \u2013 and common chainring sizes explained"},"content":{"rendered":"

Crankset BCD demystified\u00a0 <\/p>

By Oscar Huckle\n <\/p>

Published: Wednesday, 24 April 2024 at 11:00 AM<\/p>

\n\n

Not all chainrings fit all cranksets. Most chainrings mount via a four- or five-arm \u2018spider\u2019 (the arms\/spokes on the crankset). The spacing between these arms differs based on the intended gear range of the crankset, the number of chainrings it has and its intended use.\u00a0<\/p>

This size is referred to as bolt circle diameter, or BCD for short. You need to establish the BCD of your crankset if you want to replace your chainrings.\u00a0<\/p>

In this guide, we\u2019ll explain how to measure BCD on your crankset, what BCD is and why cranks use different measurements.<\/p>

We\u2019ve also provided a common crankset cribsheet to ease the job and confirm your results. You can find it at the end of this article.<\/p>

How to measure BCD<\/h2>
A digital caliper is the ideal tool to use. – Kaden Gardener \/ Our Media<\/figcaption><\/figure>

If you\u2019re lucky, the BCD measurement will be engraved or stamped somewhere on the chainring or crankset.\u00a0<\/p>

However, this isn\u2019t always the case and the best way to manually measure the BCD is with a vernier caliper, or failing that, a ruler.\u00a0<\/p>

\"Measuring
The distance between the chainring bolts on this Shimano Ultegra R8100 chain is 89.97mm. – Kaden Gardener \/ Our Media<\/figcaption><\/figure>
\"Measuring
Note how this crankset is asymmetric because of the shorter measurement in the other direction. – Kaden Gardener \/ Our Media<\/figcaption><\/figure>

On a crankset with four bolts, you can measure the distance between two bolts directly opposite each other.<\/p>

On a crankset with five bolts, you\u2019ll need to measure two bolts adjacent to each other then use a look-up table to ascertain the correct BCD:<\/p>

<\/colgroup>
\ufeffDistance between two adjacent bolts on a 5-arm crankset (mm)<\/th>BCD (mm)<\/th><\/tr><\/thead>
55.2<\/td>94<\/td> <\/tr>
64.7<\/td>110<\/td> <\/tr>
76.4<\/td>130<\/td> <\/tr>
84.6<\/td>144<\/td> <\/tr> <\/tbody> <\/table>