Charles Wahl

I know that the ISO standard for square-taper bottom bracket spindles is 6695:1991, but I'm too cheap to buy it ($30 for two pages). I've also found out that the JIS standard is D 9415:2001; that costs $36.

Does anyone know what the ISO and JIS standard dimensions/tolerances actually are, in absolute quantitative terms?

Background info: Phil Wood's bottom bracket recommendations are to use JIS for Campy cranks 1993 or earlier, and ISO for those later. This seems to be consistent with my measurements of

a) 1985-vintage Campy SR road crank spindle, compared with a Japanese spindle I have from the same time period -- the ends of the spindle squares are within 4-5 thousandths of an inch (.496 vs .500) -- if ISO and JIS cranks "fit" on 2-degree taper spindles with about 4.5 mm difference, that would suggest that the difference in end dimension would be about 12 thousandths (0.3 mm).

and

b) the Sugino and Campy crank arms I have from the same era both fit (not tightened) onto the Campy spindle with 3 to 3.8 mm clearance between end of spindle and crank bolt washer seat. Not anywhere near 4.5 mm difference.

Does anyone know about when bicycle manufacturers adopted ISO/JIS standards? In Campy's case, it appears that there was a change between 1993 and 1994 (coinciding with a time when I was not paying attention to bike issues!).

Thanks,

moxfyre

Oh dear, this is a topic that has been debated to death Here's a thorough, and thoroughly acrimonious, thread on ISO vs. JIS from rec.bicycles.tech: https://groups.google.com/group/rec.b...8716cbc6917ell

In it, Sheldon Brown gives many examples of bikes he's built with mismatched BB/crank taper. They all work fine. That's good enough for me to basically not think about the issue anymore

wroomwroomoops

I disagree: this is the first time I see someone asking for no-bull**** numbers/dimensions - and I, for one, welcome this novel idea of actually wanting to know the exact figures.

I can understand that for you, it's enough to know that stuff works with each other. But not everyone is like you; some people need to have the knowledge of the actual sizes and tolerances, and figure out for themselves, how the parts will work together.

operator

No, it just means you're too lazy to think about it. For every "it worked", there is a similar "it didn't work" thread out there.

There is a really simple rule that you need to use. If you can get the proper BB, DO SO.

San Rensho 

Agree completely. Like my high school science teacher used to say "Close enough for the girls we go with!"

Absolute precision is good, but after all, we are talking about a friction fit attachment of crank to spindle, which by definition is imprecise. The first time you put cranks on a bike, the square is going to expand and the next time you put it on its not going to fit exactly the same way it did the first time, its going to slide up slightly higher on the spindle. That expansion and imprecision I will venture to say, is more than the .3mm difference between ISO and JIS.

wroomwroomoops

Maybe some of us want to know actually why a JIS vs. ISO spindle/crankset combination will or will not work. Is it a question of the angle of the facets of the spindle? Are those angles the same between ISO and JIS, and it's actually a different cross-section area? Knowing these and similar things, is necessary to gauge how will a mismatched combo behave, at a given compression force.

So what makes this thread unique, against the other JIS/ISO threads, is that the OP does not ask for any anecdotal evidence, or opinions, but figures.

moxfyre

All the "didn't work" cases I have seen had to do with mismatched spindle LENGTH, not spindle TAPER. Of course if it's convenient to get the proper BB, do so! I don't argue with that But if you have the wrong type of ISO/JIS BB sitting around, with the right length, give it a try!

Yes, that's a good point! I just felt that, inevitably, this thread would degenerate into people arguing about whether you can swap them. So I was trying to head that off early. I certainly do not mean to disparage anyone for trying to get to the bottom of this issue, I'm sorry if I gave that impression.

The numbers are interesting, you're right, and you'll find some pretty authoritative people (Sheldon Brown, Jobst Brandt, etc.) discussing them in that rec.bicycles.tech thread I linked to. There are many other threads on taper dimensions on r.b.t as well.

HillRider

I don't have all of the exact dimensional figures but I'm pretty sure of the following:

1. Both ISO and JIS spindles have a 2° taper per side or a 4° included taper.
2. ISO has an end dimension of the square spindle that's 0.2 mm smaller across the flats than JIS.

The upshot is a JIS crank on an ISO spindle will go too far up the spindle and an ISO crank won't go far enough up a JIS spindle. This is in theory. In practice, the manufacturing tolerances allow a lot of overlap so mix-and-match is often successfully done.

Charles Wahl

I don't mean to start a religious war, truly. I have searched forums here, Google (WWW), Google Groups (Usenet) with some diligence, and I've never seen a post where someone actually divulged what the "standards" stipulate. I think that it would be useful information for someone who has a spindle or crank in one hand, and a caliper in the other, to be able to tell with reasonable certainty whether it's ISO or JIS.
Is this really the private domain of manufacturers, information too sacred to share with the unwashed?

One benefit of this would be that you could actually figure out (knowing [if Sheldon be believed, and if not him, then who?] that the bolt seat on the crank sits about 3 mm outboard of the "matching standard" spindle end when push fit, and about 1.5 mm outboard when tightened) that to get a chainline of such-and-such, purchasing a BB with a certain length/overhangs will get you close enough that a shim or two under the fixed cup will make it all work out. Without resorting to trial-and-error, or leaving that up to the LBS.

My "wild *** guess" from the pieces I have in hand, is that the JIS standard spindle end is very close to 0.5" or 12.7 mm, and that the ISO standard is more like 12.5. The actual standards include acceptable tolerances, I imagine. I also speculate that before reference to these standards was the norm, Campagnolo's "house standard" was actually just slightly smaller than JIS, but closer to that than to ISO, and that they got on the EU bandwagon in 1994 with ISO spindles.

wroomwroomoops

That's some great info there, thanks!

Interesting the 0.2 mm difference, and the fact that (in practice) the manufacturing tolerances make for very different couplings. I am really surprised, because I know I have no freakin' chance of fitting a 27.2 mm seatpost in a 27 mm seat tube.

randomgear

But a seatpost isn't tapered like a spindle.

wroomwroomoops

Good point. Probably the final position of the crankarm on the spindle depends also on the material of the crankarm and the force applied during installation.

Charles Wahl

I revised my original post because I found the standard number for JIS. Neither the NYPL Science branch, nor the Library of Congress seems to have copies of ISO standards, nor JIS; so free consultation of the original sources is out of the question there. Neither one seems to have an ISBN either.

jrstewart3

I am curious as to whether anyone has read the actual JIS and ISO standards and compared them since this was originally posted about ten years ago?

And, has anyone seen an actual spec for JIS low profile?

I am not interested in starting another holy war on whether or not you can mix and match the two, but I do have a theory why it works "sometimes".

fietsbob

People on this forum take pictures not measurements, if you have not Noticed...


Long Ago, .. as I recall, .. I Had a JIS Crank on an ISO Spindle, it went on just half way up the taper.





....

Iride01 

There are likely to be factors that the JIS and ISO don't control or manufacturers choose not to follow completely. With any standard, if you control it too tightly then there can be no improvement.

Some people will be able to mix them with little to no issues and some that will have issues. If we are talking just about the square tapers, then it's more about the starting dimension of the end and the length of the taper.

However mine is a hypothesis since I don't have either's published standards to base that on. But I do have some anecdotal experience with them.

jrstewart3

I agree with hypothesis , I looks like the the ISO standard specifies many more dimensions than JIS, but both have common 2° taper. My guess is that would explain why some people have no issue, and some do>

I think Sheldon Browns page where he illustrates proper fit is good, there was just no explanation of why is works,,,,,, sometimes.

Dave Mayer

Exactamundo. The truth.

The consequence of the small dimensional difference between ISO and JIS spindles translates into roughly 3mm as to where the crankarm sits on the spindle.

A JIS arm on a ISO spindle sits closer in. Risk: you may run out of taper, leading to the arm 'bottoming-out'. Then, in order to tighten adequately, you may split the arm.

ISO on JIS: this sits about 3mm further outboard. Risk: is there enough arm engagement on the taper to withstand pedaling forces?

robmonk

Thank you!

Someone asked for NUMBERS

The thread gave OPINIONS

There must be 1000 bike shops monitoring this thread who can measure stuff and provide NUMBERS.

For example, I'm trying to come up with a custom version of FlexiRide torsion suspension half-axle spindle mounts, and it seems like since I'm trying to get a 20mm wheel spindle on the end of my torsion cam arm for the wheel hub, maybe using a pedal crank arm might make sense... 30 minutes of searching later, this thread where you FINALLY provided some solid numbers below a bunch of argument, is the first place where I've encountered anything but kvetching about varying standards in qualitative terms. I'm trying to rig a raw square tube end to an off-the-shelf crank arm, and the discussions without numbers don't help for that.


So it seems the small end of the tapered section of a crank spindle is 0.500 inches +/- (mostly minus) a few mm. That's great!
It seems there's wide agreement the taper angle is 2deg (important: per face of the square taper, so 4deg total x trigonometry of tapered length for the hypotenuse?)

NEXT: - What are some of the measured dimensions of the larger end (projected) face of the square taper? On how long of a tapered section were these measurements taken?

- Are crank arms tapered on the female socket of the crank arm, to match the ISO / JIS standards? Or are they just straight square? If the female socket is tapered, is it 2deg (per face?) like the spindle, or is it some shallower taper to allow for fit?

Andrew R Stewart 

People do what benefits them. So if LBSs had the time, the many combos of parts, the measuring tools (and calipers are not that) and the skill to understand what you read out than we would likely have the info easily available.

Oh, wait, someone tried that already (The Sutherland's Manual) a few decades ago with the known parts and "standards as was then. Andy