Originally Posted by
EdIsMe
I did a bit of research and found that ISO and French headsets both have the same steer-tube insertion diameter of 30.2mm. This means that converting to 1" threadless is definitely possible and probably something I will do as soon as the budget allows.
Yes, the only differences between French and standard US is/was the threads on threaded steerers AND A 0.1 MM LARGER CROWN RACE ON THE FRENCH. That slightly smaller crown race diameter on the threadless fork should make no difference at all especially if you use sealed cartridge bearings. They don't depend upon perfect fit with the nominal external crown race like loose balls used to. Besides the crown races for use with sealed cartridges are often split nowadays to allow easier installation on the fork. That makes 0.1 mm insignificant.