58 mm, the small ring for compact triple 5 bolt crank arms (94 mm for the large ring, if there would be a large ring).
This looks like the chaninrings of the Shimano Alivio FC-MC12 crank, with the 3 chainrings riveted together and bolted to the crank spider with only those 5 bolts. I”d say pretty useless in this day and age.
jncoeveryday on
I bet it’s 94.
Don’t need to bother with paper, geometry and stuff, just use Sheldon’s Cribsheet.
Not a great measuring device but the second picture looks like 38-39mm between adjacent holes on a 5 bolt pattern… which would be too small for the standard granny ring 74mm BCD. I think what you have is something proprietary to that crank.. which is supported by the fact that it looks like the three rings are riveted together. You likely need a different crank/chainring entirely. They aren’t all a standard size.
This is a chainring set all riveted together. I don’t think you will find this set without just buying a new mountain bike crankset with the rings already attached. I don’t believe these were ment to be replaced as chainrings, only as a complete crankset.
8 Comments
60 as a guess: you are not measuring it in those pics.
Mark through the chainring bolt holes onto a piece of paper.
Get a compass and use it to trace a circle that goes through the center of the five marks you have made.
Measure the diameter of that circle.
Probably 110bcd
Wolf tooth made an article on how to measure it, including a paper guide
https://www.wolftoothcomponents.com/pages/how-to-measure-bolt-circle-diameter-bcd
58 mm, the small ring for compact triple 5 bolt crank arms (94 mm for the large ring, if there would be a large ring).
This looks like the chaninrings of the Shimano Alivio FC-MC12 crank, with the 3 chainrings riveted together and bolted to the crank spider with only those 5 bolts. I”d say pretty useless in this day and age.
I bet it’s 94.
Don’t need to bother with paper, geometry and stuff, just use Sheldon’s Cribsheet.
Refer to Shelly Brown: [the infamous BCD crib sheet](https://www.sheldonbrown.com/cribsheet-bcd.html)
Not a great measuring device but the second picture looks like 38-39mm between adjacent holes on a 5 bolt pattern… which would be too small for the standard granny ring 74mm BCD. I think what you have is something proprietary to that crank.. which is supported by the fact that it looks like the three rings are riveted together. You likely need a different crank/chainring entirely. They aren’t all a standard size.
[“Sheldon Brown’s Bicycle Crank/Chainring Bolt Circle Diameter Crib Sheet”](https://sheldonbrown.com/cribsheet-bcd.html)
This is a chainring set all riveted together. I don’t think you will find this set without just buying a new mountain bike crankset with the rings already attached. I don’t believe these were ment to be replaced as chainrings, only as a complete crankset.