Originally Posted by
Little-Acorn
Hmmm, well, the chains cross close by each other now without interference. I don't see why they would clash due to closer gear size, they seem well enough separated now. Then again, I've never tried it
Currently the chain on the 39T drive chainring is always above (or "outside" of) the 36T synchronizing chain so they never really cross. If there is enough side clearance so they can be adjacent without interfering, then a smaller drive chainring will work but be sure they will clear.
Originally Posted by
Little-Acorn
Here's a silly question: How do you measure the bolt circle diameter? Distance from the center of one bolt, to the center of the crank, times two? Or is it the distance between two far-apart bolts (wouldn't be the mathematical diameter, but maybe tradition is stronger than math?)?
With a 5-arm crank, you can't measure the bolt circle directly but RG's posting gives you the spacing between the centers of adjacent chainring bolts that corresponds to common bolt circles. If you want the trigonometry that goes into calculating these numbers, PM me.