Originally Posted by
kcblair
Thanks, help me determine that length . I'm using a double at now. I would like to go from a FSA Compact 34/50T to a 30/46T compact. Leaving the BB alone.
You could just buy a new 46 tooth ring for your current crank and call it a day. That is of course if anything else isn't worn out.
If you do go the new crank route, as Fietsbob says, it is a trial and error method of obtaining the right bottom bracket length. My guess is no change is needed.