Originally Posted by
79pmooney
Edit: No one mentioned the two tapers. Bottom bracket spindle come in ISO and JIS tapers. Both use 2 degree taper but he difference is how thick they are. The difference makes a 4.5 mm difference on where the cranks sits. Lifted from Sheldon Brown's excellent website "If you install an ISO crank on a J.I.S. spindle, it will sit about 4.5 mm farther out than it would on an ISO spindle
of the same length." (
https://sheldonbrown.com/bbtaper.html)
Ben
For clarity: the
Rene Herse site says it moves each crank arm by between 2mm and 2.5mm.
Both are credible sources of info. Rene Herse and the late Sheldon Brown are consistent if Sheldon Brown was quoting the total difference in spindle length required for interchange, which would be divided between the two crank arms.
I believe that to be the case, but I haven't tried mounting the same crank on both to verify.