So here we go. Let me start off by saying that all of the above links, including but not limited to Velo-Orange, Phil Wood and Sheldon Brown/Harris Cyclery all have mis-information. Because they're all inked to one another they are all guilty of having this mis-information.

Here is the mis-information: ISO taper is longer than JIS taper. NO. Pre '94 Campagnolo cranks are JIS. NO. I'm not saying my inofrmation is 100% correct but what I'm saying is the information in the above links is mis-information. I've been wrong before, I'll be wrong again but I always man-up when I am wrong.

Phil Wood quote:
Sheldon Brown/Harris Cyclery quote:
An easy way to think of the JIS/ISO issue is to think of it as a fat/skinny issue verus a taper angle or taper length issue.

JIS = fat BB spindle w/ a larger crank opening. Think fat Japanese Sumo wrestler to associate JIS w/ being the fatter of the two.
ISO = skinny BB spingle w/ a smaller crank opening

Taper angle: Essentialy the same between JIS/ISO. If there is a difference it would take very expensive lab quality equiptment to measure it. Its my opinion within standard there probably enough tolerance differences that there's an overlap between the 2 and thats assuming there's a difference between them

Taper length: JIS spindles have a longer useable taper length than ISO spindles. This contradicts whats found in the above links which suggest ISO spindles are longer.

A good analogy is the childrens toy with the colored rings. Think of the green ring as being JIS/fat and the blue ring as being ISO/skinny. While the cones angle remains constant (taper angle) the green ring with its larger JIS/fat opening will always go on farther than the blue ring with its ISO/skinny opening and vice versa.



With all due respect to Phil Wood its my opinion that older Campagnolo cranks are of the ISO variety which counters what his website suggests in regards to pre-'94 cranksets and BB's. My mid 70's and 80's Record cranks simply do NOT slide onto the fatter JIS Shimano spindles I have. Sheldon Brown/Harris Cyclery does list the Campagnolo cranks as being ISO/skinny cranks. It is possible that older cranksets weren't built to any specification and its us, in our modern world, trying to fit them into a classification that never existed. Who knows.

I measured 8 different BB spindles, 3 JIS/fat and 5 ISO/skinny for 3 dimensions:

Spindle tip width
Spindle width inboard 11.85mm in from the tip (my measuring device is 11.85mm wide)
Useable spindle length: Simply how long the spindle taper is from the tip until the taper ends.

Spindle Tip Width JIS: Average 12.69 w/ 12.66 low and 12.72 high
Spindle Tip Width ISO: Average 12.60 w/ 12.55 low and 12.67 high

Spindle Width Inboard JIS: Average 13.56 w/ 13.53 low and a 13.61 high
Spindle Width Inboard ISO: Average 13.36 w/ 13.25 low and 13.40 high

Useable Spindle Length JIS: Average 16.92 w/ 15.73 low and 17.64 high
Useable Spindle Length ISO: Average 15.99 w/ 14.00 low and 19.10 high (with the excpetion of the 19.10 spindle all others were shorter than the JIS avg)

So there you have the not so low down on the JIS/ISO issue as measured in my lab (garage). The 8 spindles measured up were:

JIS/fat:
Shimano UN73
Shimano unknown cartridge
Shimano 600 EX

ISO/skinny:
Campagnolo Record mid-70s
Camagnolo early cartridge
Stronglight early 70's
Sugino 75 road
Suntour cartridge track