How To Measure Chainring Bcd

Figuring out what size chainring you have is pretty easy, it's just a matter of knowing what size bolt circle diameter (or bcd) you have. It can be somewhat difficult to make this measurement if you don't have a caliper since the crankarm gets in the way.


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To determine the bcd of your chainrings, measure the distance between two adjacent chainring bolt holes from center to center.

How to measure chainring bcd. Alternatively you can measure the distance between two adjacent bolts and use the table below to determine the bcd. On bicycle chainrings, this dimension is usually measured in millimeters. If it is not labeled on your chainring you will need to measure it.

What is the bolt circle diameter? You could measure the distance from the bb spindle to the center of one bolt hole (gives you the colt circle radius) and double it. For the stout crankset we recommend the 10mm bolts or the bolts that come with the crankset.

The image below shows this measurement on a 104mm bcd chainring. Bcd = colt circle diameter, the 4 or 5 bolts are arranged in a circle, the diameter of which is the bcd. Many chainrings have the bcd shown on them but if it isn’t, you’ll need to calculate it.

When ordering a chainring make sure you get one which has the same bolt spacing pattern, although from this page i'd say you have evenly spaced bolts. Use the measurement (x) to find your bcd on the chart below. 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.

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Notes for those the plan to run a 32t chainring on a. All you need to do to calculate the bcd is measure the hole spacing a between adjacent holes, count the number of holes n and plug them into the equation above to calculate the bcd. I believe sheldon brown also has a table of distances from one bolt to the adjacent one for each bcd.

This is the easiest method to use for chainrings with five bolts. All the sizes are given in millimetres (divide with 25.4 to get inches). Alternatively you can measure the distance between two adjacent bolts and use the table below to determine the bcd.

Multiplying this dimension by 1.7 will give you the actual bcd for a 5 bolt chainring. Think of an imaginary circle drawn through the center of each bolt on your chainring—there’ll be 4 or 5 of these depending on your spider. The image below shows this measurement on a 104mm bcd chainring.

This will give you the bcd for a 4 hole. Bcd is an acronym for bolt circle diameter. Classic methos how to measure bcd is:

With this measurement (b) you can refer to the table below to identify the corresponding bcd, or use one of the following equations: How to measure bolt circle diameter on a chainring? Threaded for standard m8 chainring bolts.

Chainring b olt c ircle d iamater guide. For the xx1 spider, we recommend the 6mm bolts (or any short m8 chainring bolt). Knowing the bolt circle diameter—bcd for short—is essential when considering any kind of chainring change.

On a chainring with 4 bolts the bcd is the distance between two bolts across from each other. I am looking to put a narrow wide ring on, i think the outer ring is too big to fit a 32 tooth nw ring. The bolt circle diameter (bcd) is the diameter of the circle that passes through the centre of the bolts on your chainring.

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Working out the bcd for a chainring or bash guard. It is critical to know the bcd of your crankset when you are selecting a new chainring for your bike. If you have an odd number of bolts you can measure between the axle and a bolt and double it, or if the bolts are evenly spaced measure between bolts and look up the bcd on this page.

All other sizes require single ring specific bolts that are ~6mm long. These rings fit any 104 bcd crankset, and here are instructions on how to measure your bcd. How to measure bolt circle diameter (bcd) bolt circle diameter (bcd) is the diameter of the circle that goes through the center of all of the bolts on your chainring.

On a 4 bolt chainring you can simply measure the distance between the centres of opposite bolts. Here are instructions on how to measure your bcd. This is usually easier to measure directly than the actual bolt circle diameter.

Since the bcd probably isn't stamped on your crankarm, you need to take a measurement and do a calculation. The outside chainring bcd is stated on crank as 120, the inner is not given. On a chainring with 4 bolts the bcd is the distance between two bolts across from each other.

A quick way to find out is to measure the distance between the center of two adjacent bolt holes then refer to the chart.


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