In this article we’re going to delve into determining the correct chainring compatibility with your crank. If you know what to look for this is a piece of cake.
In my case I decided to swap out the existing Deore XT crankset for a CODA Tarantula crankset for my 1994 Cannondale Super V.
The Deore XT crankset is a triple with 22-32-42 chainrings. The CODA Tarantula however, is a dual 29-44 setup. And although it didn’t look worn, there’s something wrong with my drivetrain.
I have changed both the chain and cassette on this bicycle. And when you renew any part of your drivetrain, but leave an old part in place, like this chainring, you run the risk of the chain slipping.
And, unfortunately, I believe that’s the case here.
Normally, I would replace the entire crank, since buying new parts is usually more expensive than buying an entire used crankset. However, since the CODA cranksets are pretty rare and expensive, this time I decided to swap out this failing chainring.
CODA cranksets are rare, but CODA chainrings are even more rare, so even if I could find a replacement on Ebay, it would probably cost a fortune. Since I didn’t find it anyway, it was up to me to determine what chainring would be compatible with this crank.
Video Tutorial
Riveted Cranks
Not all cranksets have replaceable chainrings. Some low-tier cranks have the chainrings riveted in place. This always kind of baffled me, since you need to replace an entire triple if probably the middle chainring is used up, but that’s the way it is.
I’ve read you can drill them out and replace them with chainring bolts, but you’re probably better of replacing these type of cranksets with one that uses replaceable chainrings in the first place.
That being said, I can understand if you still want to perform such an operation for restoration’s sake. And sometimes you’ll want to keep a certain crankset in place from a design perspective.
Chainring Bolts
If the crank has chainring bolts, it means the chainrings can be replaced.
You may need a chainring nut wrench loosen really tight bolts. Or you can make a DIY chainring nut wrench from a coin.
Using crank brand and type to determine chainring compatibility
Clearly not all cranks are the same. In my case the right crank, which holds the chainrings, has 5 points to place the chainring bolts. Most older style triple-cranksets have a five-bolt setup.
One of the easiest ways to determine which chainring is going to be compatible with your crank is to simply type in your brand, type, groupset, and type, added with “chainring”, and possible the amount of teeth you want. You can find the type of the crank located at the back of it.
For example if you search for “Deore XT FC-M770 chainring 32t” you’ll immediately get multiple correct results, since the chainrings are still available.
You can use this same approach to find older chainrings on Ebay or similar online marketplaces.
Using Bolt Circle Diameter (BCD) to determine chainring compatibility
If you can’t find the same type chainring because of its rarity or you’re unwilling to spend the type of money being charged for NOS parts, you’ll need to know the chainring compatibility with your crank.
You can do that by measuring the bolt-to-bolt length (A) and use that metric in combination with the number of bolts necessary to tighten the chainring to determine the Bolt Circle Diameter (B).
- BTB = Bolt-To-Bolt
- BCB = Bolt Circle Diameter
In my case, with a bolt-to-bolt length of 55,4mm. and 5 mounting points, the BCD for my chainrings needed to be 94mm. You can find your BCD in the chart below.
Chainring BCD Chart
BCD (mm.) | Bolt Mounts | BTB (mm.) | Common Application |
|---|---|---|---|
58 | 5 | 34.3 | Compact MTB triple – inner |
64 | 4 | 45.3 | Standard MTB – inner |
74 | 5 | 43.5 | Compact Road double/triple – inner |
80 | 4 | 56.6 | SRAM MTB double – inner |
86 | 3 | 74.5 | FSA 3-bolt |
88 | 4 | 62.2 | XTR M985 – inner/outer |
92 | 5 | 53.3 | Dura Ace 7800/Ultegra 6700 triple – inner |
94 | 5 | 55.4 | Compact MTB triple – middle/outer |
102 | 4 | 72.1 | XTR M960 – inner |
104 | 4 | 73.6 | Standard MTB – middle/outer |
110 | 5 | 64.7 | Compact Road double/triple – middle/outer |
110 (Campy) * | 5 | 64.7 | Campagnolo Compact/CX – inner/outer |
120 | 4 | 84.9 | SRAM MTB double – outer |
130 | 5 | 76.4 | Standard Road double – inner/outer |
135 | 5 | 79.5 | Campagnolo Road – inner/outer |
144 | 5 | 84.6 | Track |
146 | 4 | 103.3 | XTR M960 – outer |
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