French, ISO, & JIS Headsets - telling them apart

dirttorpedo

Senior Retro Guru
So I was just reading on the Velo Orange blog about the various headset standards. One thing that jumped out at me was the comment that forks designed for French style headsets typically have a flattened area at the back rather than the notch common to ISO. My frame is an Ellis Briggs, but it has the flattened back to the fork and the headset has no spacer. I'm wondering if this is a signal that it uses a French headset rather than an ISO one.

Yes, this is related to my increasingly frustrating attempt to convert the bike to centerpulls.
 

mdvineng

Senior Retro Guru
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Ignore velo O. Plenty of bikes either have a flat/notch or other method of pinging off the crown race, or more likely none at all. Measurements are the critical point.
 

jim haseltine

Old School Hero
Chances of French threads on a British frame? Pretty near zero. French manufacturers were moving away from French threading as early as the 1980s - we used to get French bikes with mixed threads, 'English' BB, pedals and freewheels but French headsets. French stuff became so unusual that I still remember the last item I saw before I left the trade in the mid 80s - a Campagnolo Record BB which had been supplied in error.
 

dirttorpedo

Senior Retro Guru
Ok, thanks guys. That's what I thought. I have a 70's vintage British built frame and had trouble believing it was designed for a French headset, but it was bespoke and I've been having issues with ISO headsets on it so you never know.
 

mdvineng

Senior Retro Guru
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You can have problems mixing components like headsets, as they can have different bearing surface dimensions despite being ISO/JIS etc those std's only refer to frame fit dimensions and threads.
 

pigman

Old School Grand Master
The flattening is nothing to do with french threading. It's about fitting a spacer with a tab between the race and locknut so it don't move when you adjust the headset.
French headsets have a smaller steerer tube, you won't fit a french headset onto an English steerer
 

Rod_Saetan

Old School Grand Master
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I would add that I have seen a lot of forks with a tapered flat on the back, and most of these are French thread. British/ISO forks tend to have a notch rather than a flat. But yes, your best bet is to just measure it accurately!
 

dirttorpedo

Senior Retro Guru
I would add that I have seen a lot of forks with a tapered flat on the back, and most of these are French thread. British/ISO forks tend to have a notch rather than a flat. But yes, your best bet is to just measure it accurately!
Yes, still haven't gotten out to buy a digital caliper yet.
 
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