# JIS or ISO Headset?



## turbomatic73 (Jan 22, 2004)

Anyone care to take a guess on what size headset I need for my mid-80's Bianchi Strada LX? It's a cheap/lower-end frame made in Taiwan...not sure if I need to get a JIS headset or ISO. The headset on there now is real cheap looking...also very badly pitted. THANKS...


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## Dave Hickey (Jan 27, 2002)

turbomatic73 said:


> Anyone care to take a guess on what size headset I need for my mid-80's Bianchi Strada LX? It's a cheap/lower-end frame made in Taiwan...not sure if I need to get a JIS headset or ISO. The headset on there now is real cheap looking...also very badly pitted. THANKS...


Can you measure the race diameter? JIS would be 27.0....vs 26.4 for ISO


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## turbomatic73 (Jan 22, 2004)

Just measured it. The inside diameter of the headset's crown race looks like it's 26.4 (half way between 26 and 27)...but the outside diameter of the fork itself (the crown race seat) measures 27 spot on. So...now I'm more confused...Do I go by the measurement of the headset's crown race or the fork's crown race seat? 

THANKS!!!


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## FBinNY (Jan 24, 2009)

You need to measure again, especially if the crown race came off the fork. A 26.4 crown race wouldn't fit onto a 27.0 crown without splitting. The maximum amount of interference is 0.05mm. The races are usually very close to the nominal size with the fork crowns being slightly over.

A JIS fork would measure 27.05 to accept a 27.0 crown race
An ISO fork would measure 26.45 to accept a 26.4 race

There's a bit of tolerance in these dimensions, but crown races are very brittle and the fork crown too rigid to shrink much so there's not much room for variation.

In any case, I think that when you measure, you'll find that you need an ISO (26.4/27.2) headset, since a Taiwan made bike wouldn't be JIS unless it was intended for the Japanese market.

Usually when we see JIS outside of Japan it's only on bikes made there.


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## turbomatic73 (Jan 22, 2004)

Double/triple checked the measurements and they are the same as I originally posted...i think it's my cheap calipers...maybe the inside/outside diameter arms aren't calibrated correctly. Plastic pieces of junk I bought at a flea market...

I'll go ahead and assume it's ISO for the purposes of ordering a new headset. If it doesn't fit I know a shop that will mill down the crown race seat for me. 

THANKS


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## Kerry Irons (Feb 25, 2002)

*Hold on!!!*



turbomatic73 said:


> Double/triple checked the measurements and they are the same as I originally posted...i think it's my cheap calipers...maybe the inside/outside diameter arms aren't calibrated correctly. Plastic pieces of junk I bought at a flea market...
> 
> I'll go ahead and assume it's ISO for the purposes of ordering a new headset. If it doesn't fit I know a shop that will mill down the crown race seat for me.


The sizes mentioned (27.0 JIS and 26.4 ISO) are the crown race seat diameters. It has nothing to do with the steerer tube diameter (those are all the same). From everything you have said, you need a JIS headset.


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## FBinNY (Jan 24, 2009)

turbomatic73 said:


> Double/triple checked the measurements and they are the same as I originally posted...i think it's my cheap calipers...maybe the inside/outside diameter arms aren't calibrated correctly. Plastic pieces of junk I bought at a flea market...
> 
> 
> 
> THANKS


One thing you can do is to sort of calibrate the caliper by measuring the steerer tube, which is reliably 25.4 for both JIS and ISO forks. 

Measure that and see what you get, than use the difference between that and and 25.4 to correct the reading you get at the crown seat. 

You should also be aware that precision measurements require a bit of touch. 

Eons ago I apprenticed at a machine shop. Before the owner let me out on the shop floor he handed me a micrometer and a bunch of parts to measure. It took me hours to get to where I could consistently give him the correct dimensions. Then he wrote my name on the mic. I was using and sent me out to do inspections of finished parts.


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## onespeedbiker (May 28, 2007)

There's a lot of confusing information here, so if I didn't make it clear please ask questions; however you are going to need a relatively accurate caliper; a good plastic one is accurate enough as long as it calibrated to 1/10 millimeter. 

First, even though the Strada LX was made in Taiwan, it should have an Italian headset which is common in all Bianchi bikes before 2000; they were primarily made near ISO standard; the crown race being 26.5, however some were made with a 27mm crown race so the headsets could utilize a wider variety of forks. I think you may have your nomenclature confused. The the crown race is pressed onto the the crown race seat of the fork. Your measurements indicate the crown race seat (27mm) is considerably larger in diameter the race at 26.5; by .5mm. While it is possible that someone pounded a 26.5 crown race on a 27mm race seat, I would think the race and seat measurements would have been somewhat altered by this process. If, OTOH you have the reverse, where the crown race ID was 27 and the race seat was 26.5 that would be a common mismatch mistake. Either way it was not unusual to mix and match crown races in the same headset to fit different forks (many fork manufactures in the 90's purposely made JIS forks so they could fit either JIS or be turned down to ISO size). 

To answer you question; first there are no more Italian headsets but in your case I would say an ISO will work, depending on your fork race seat measurement. If it's 26.5 you want ISO; if it's 27 you will probably want ISO with a JIS crown race. This is because Italian headseats had the same size frame cups for either 26.5 or 27 fork races, but JIS cup races are .2 mm smaller so the cups will be too small to press in. OTOH your Bianchi could simply be spec'd for a JIS headset (with a 30mm headtube ID), but I seriously doubt it.


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