Originally Posted by
joejack951
Bolt hole size complicates measuring a little bit. You'll have to eyeball the center of the hole. You can buy hole center attachment pieces for calipers. I have a set for mine.
However, the bigger issue is that for a 5 bolt chainring, simply measuring between any two bolts tells you nothing. You need to do some geometry to calculate the circle that will pass through three of the holes (which will get the other two by default). If you drew the triangle that went through three of the bolts, you could use that determine the BCD fairly easily, especially if you were using a CAD program. I could post some pictures/measurements if anyone is interested though it will have to wait until at least tomorrow as I have the biggest CAD headache I've had in a while trying to update parting lines on some molded plastic parts.
Sheldon Brown says
"Measuring BCD: This 110 mm BCD ring measures 64.7 mm center-to-center.
Multiplying this dimension by 1.7 will give you the actual BCD for a 5 bolt chainring.
Use 1.4 for 4 bolt chainrings"
Easier than CAD, and more portable too.
To the OP: all you need to made a 1X (whatever) is a single chainring, and a pair of short stack chainring bolts. A short cage derailer can handle the chain wrap from just about any setup I could imagine, and a road derailer will easily handle a 28 tooth big cog. If you wanted more range, and switched to a 11-34, then you would need a mountain derailer.