I have a square taper bottom bracket. How can I tell whether it is a J.I.S. or ISO taper with a minimum amount of disassembly?
FWIW, it's a Ritchey from 2004. However, it would be nice to get answers that apply to other brands as well.
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I can't find anything that states exactly what size the taper goes down to either, so you would need a known JIS/ISO to compare with. Other sources conform they are the same angle though. Minimum disassembly will be taking off one crank.
The easiest method is measuring the outmost part of the spindle, like the answer of Pedalphile suggest, however there seem to be differing measurements.
These are the values I found(source in german):
ISO 1991: 12,50 mm
JIS: 12,63 mm
ISO 2015: 12,73 mm
I was able to to reproduce the ISO 1991 value by measuring my own bike.