[Mountain Cycle Shawn]

I have a couple Truvativ ISIS cranksets with 22, 32, 44 rings. Am I right in saying that the middle ring bolt pattern size is 74mm and the large ring bolt pattern size is 110mm, even though they are mounted together using the same hole?

 

[FBinNY]

If they're mounted on the same holes with common bolts the chainrings obviously have the same BCD.

The most common arrangement is middle and outer are both 110mm and the smaller inner mounting pattern is 74mm.

 

[Mountain Cycle Shawn]

So, they must be measured across from each other. They don't measure from one chainring bold to the one next to it. Because my middle/large chainring bolts are 110mm from one to the one across from it and 74mm from one bolt to the one next to it. that's why I was confused.

 

[FBinNY]

So, they must be measured across from each other. They don't measure from one chainring bold to the one next to it. Because my middle/large chainring bolts are 110mm from one to the one across from it and 74mm from one bolt to the one next to it. that's why I was confused.

It's none of those measurements. it's the diameter of the circle they all lie on. If you have an even number of bolts you can measure across opposites. But with 5 bolts, none are opposite any others, so there's no way to do a direct measurement.

If you wish you can measure the on center distance between adjacent holes and use the conversion crib sheet here,

 

[Mountain Cycle Shawn]

Ok, got it, thanks.