Dumb Question: Threaded Fork Headset Crowns
 

I think this is a dumb question but here goes...

I just purchased a threaded fork that has a crown race installed. Assuming the crown race is in good shape (not pitted) and a standard size, will it be compatible with any standard threaded headset I buy (regardless of the actual crown diameter e.g. 27.0 or 26.4)?

Thanks!

Possibly it'll fit your new headset but odds don't favor it. Crown IDs are standardized to match forks, but all other details are internal to the headset design and don't match across brands. Often a given company will use the same crown dimensions for all their headset models, but that's about as close as you get.

In some cases a crown will be close enough to work with another headset, But you'll have a large gap between the crown and cup allowing weather and dirt to enter, or there may be other issues making it less than ideal.

Cool, that makes sense.

Does anyone know definitively what size crown a Tange 5 fork would have? I'm getting super antsy to get this build rolling, but I'll probably end up waiting until I actually get the fork in the mail before I order the headset anyways.

Could be either 26.4 or 27.0 depending on the intended market. 27.0 or JIS (japan industrial standard) if intended for the Japanese market, 26.4 (ISO) if intended for export to the USA or Europe.

You need to also need to be concerned about your frame. JIS headsets will have 30mm cups, ISO will be 30.2. You'll notice that both the frame and fork can be changed from JIS to ISO but not the other way around. If either the frame or fork is ISO, buy an ISO headset, and have the other component converted.

I believe my frame is ISO (Mercier Kilo TT, specs say it uses a fork with a 26.4mm crown). I'm hoping the fork is ISO, but if it's JIS I should be able to have an LBS mill the crown down, right? I need to have the fork taken in for the cutting and some additional threading anyways.

Thanks for your help!

Yout frame is very likely to be ISO, and so is the fork. But, in any case, JIS frames and forks can easily (for a bit of dough) be changed to ISO. In many cases forks need to be milled anyway, so no issue there.

If it's not a Japanese headset part, it's highly unlikely to be JIS diameter.

Unfortunately, if it is a Japanese headset part, it could be either JIS or ISO. You won't know until you remove the race and directly measure the seat diameter.

The good news is that it is trivial to mill JIS crown race seats to accept ISO headsets.