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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.

Reid
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    I'm a little disappointed that Sheldon doesn't give some measurements you could mike. Based on Google, only one person has ever chosen to measure the the two, and he declined to publish his numbers. (BTW, he claims that the JIS taper is 1.7 degrees vs 2 degrees for ISO.) – Daniel R Hicks Jul 04 '12 at 18:53
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    On that link you posted, it lists various manufacturers that use each type of taper. Ritchey is listed under J.I.S. The general rule of thumb is that Japanese bikes use J.I.S. and that European makes use ISO. Also, from the article you linked to, they are mostly interchangeable. – Kibbee Jul 04 '12 at 19:33
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    Also in the Sheldon article, is says that both have an angle of 2 degrees, but that ISO spindles are longer, and taper down to a smaller end. – Kibbee Jul 04 '12 at 19:52
  • @Kibbee, yeah, I saw that Ritchey was in the JIS list. I'd love some way to verify that independently. Regarding the interchangeability, it sounds like the length spec gets confusing, so I'd like to avoid that. – Reid Jul 05 '12 at 03:20
  • I know that in general it is a safer to use an ISO crank on a JIS taper, and less reliable to use a JIS crank on an ISO taper (because the longer/smaller taper end poses a risk of poking all the way through your crankarm. However, I've never done it but Sheldon says it is OK.) – WTHarper Jul 05 '12 at 15:11
  • I'm commenting because this isn't yet worth an answer. I think the bike manufacturer is secondary. The bigger question may be what brand of crankset and BB are involved. Campagnolo cranksets will be ISO, that one is easy. I am thinking that everyone else is likely to be JIS, but I'm not absolutely certain of this. Shimano cranks are obvious, and they may be the majority of the cranks involved. Questions remain about the rest... I think Specialties TA (French manufacturer, but fairly high end and rare in the US) is exclusively or maybe mainly JIS. – Weiwen Ng Aug 03 '21 at 22:30
  • TA and Stronglight used to be ISO but switched at some point. As far as I know old European brands were generally ISO. – ojs Aug 04 '21 at 09:09
  • @ojs Lordy, looks like I was wrong. I can at least say that more current TA is JIS, because I have a TA Carmina with a JIS BB. TA themselves may not have documented it very well, but the US importer was very clear that it was a JIS crank. – Weiwen Ng Aug 04 '21 at 11:41
  • @WeiwenNg My guess is that the importer emphasized it's JIS because TA used to make cranks to ISO spec and for example https://www.peterwhitecycles.com/carmina.php doesn't mention the JIS version at all. TA themselves doesn't tell which standard they use or when did they switch. – ojs Aug 06 '21 at 06:34
  • Possibly related - https://bicycles.stackexchange.com/questions/82368/ – Criggie Jan 05 '22 at 00:52

5 Answers5

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The width across the narrowest part of the flats (end of spindle):

JIS = 12.65mm

ISO = 12.33mm

Use calipers.

Pedalphile
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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.

L. Borchert
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  • Does anyone really use the new ISO standard? As far as I know Campagnolo was the last one to use ISO and they switched to two piece system before 2015. – ojs Aug 04 '21 at 05:29
  • @ojs certain (expensive) track cranks (by japanese manufacturers!) still use ISO. it isn't clear if they use the newer standard. – Noise Aug 04 '21 at 06:40
  • @JoeK Which ones? – ojs Aug 04 '21 at 08:39
  • Sugino would be one example @ojs – Nate W Aug 05 '21 at 23:15
  • Interesting. I have Sugino Pista cranks on one bike, they were sold as JIS and fit on JIS BB as they should – ojs Aug 06 '21 at 05:29
  • I was going to say that I would have thought that Sugino, since it's a Japanese brand, would be JIS for sure. If you google for Sugino BBs, at least the track BBs on the first page are clearly described as ISO. I didn't delve into the results. – Weiwen Ng Aug 06 '21 at 15:38
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This is a minor answer expanding on a comment I made to the original post. If the crank in question was Shimano, then the BB has to be a JIS taper, unless someone didn't know that Shimano square taper cranks have always used the JIS taper. Similarly, a Campagnolo square taper crank would always use ISO taper.

Unfortunately, with other crank manufacturers, the picture may be less clear. For example, as ojs pointed out in comments, TA and Stronglight (two French manufacturers) probably used ISO for a long time, but I can confirm that current TA square taper cranks are designed for the JIS taper, because I have one. ojs points out that older European brands may be ISO.

The bike model and year may not offer us much information if we know the crankset and BB in question. A 2004 Ritchey road bike could conceivably have been built up with Shimano or Campagnolo cranks, or maybe even some obscure third party if the owner wanted that. If it were a mountain bike, then I'm less familiar, but I assume that would shift the potential set of components away from the smaller European brands, so I would assume that the JIS taper is more likely.

Weiwen Ng
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    Still nitpicking, the question could be read that it's a Ritchey bottom bracket. Ritchey used to sell bottom brackets and cranks under their brand, and the concensus seems to be that at least the cranks were JIS. – ojs Aug 06 '21 at 06:38
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You could use a known JIS/ISO to compare to.

Other sources confirm they are the same angle though. Minimum disassembly will be taking off one crank.

http://www.urbanvelo.org/issue15/urbanvelo15_p86-87.html

http://www.velodromeshop.net/index.php?p=catalog&parent=217&pg=1

I can't find anything that states exactly what size the taper goes down to.

Criggie
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armb
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ISO? It may be something like 14mm, measured at the flats; in other words the diameter of the spindle. JIS is probably measured at 16.9mm.

G. Haley
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    Is that correct? This contradicts a previous answer, plus it’s not 100% clear where you are measuring. – Weiwen Ng Jul 25 '22 at 01:52
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    "maybe something like" and "probably" doesn't sound like they actually measured anything – ojs Jul 30 '22 at 19:40