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Nitto's measurement systems are very consistent, they just have several.
Defining the same measure "extension" in different ways for different stem products is inconsistent, i.e., lacking consistency in the definition of a quantity, rather than consistency over time.
I started this conversation because the LFGSS threads on stem measurement mentioned in several places that Nitto stems seemed to be about 10mm longer than expected as they use their own measurement system. It turned out that Nitto use two measurement systems which give different values for extension. I thought the information might save someone having to return a mail-order stem that was longer than expected. In my case, I'll measure carefully using the appropriate diagram for the model and hope for the best when ordering.
[ edited after comment from @pop.zr, to correct the direction of the difference reported in earlier LFGSS threads ]
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Did you mean to say that the stems end up longer than expected? That would certainly be the case with the Pearl (NP) quill stems. For example they are advertised as, let's say, Pearl 10 (100mm), and they end up as ~105 - 110 mm, measured along the stem extension itself, like most stems are measured. Following the diagram that you provided, and the diagrams from their catalog http://nitto-tokyo.sakura.ne.jp/Catalog.pdf it shouldn't be too hard to figure out, since there is a diagram explaining the measurement method for almost every model.
But I wonder what would the measurement method be for the NJ-89 stem. There is no measurement diagram for that model. If we assume that they use the same method as for other threadless stems, it would be ok, but it is possible that they are measuring them as the Pearl models, perhaps because they are both NJS approved models, used for keirin racing, so it might be the case. Some NJ-89 stems looked a bit longish for the given length, on photos, although I haven't measured any or seen it in person.
Does anyone have any experience with the measurement of the NJ-89 model?
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Did you mean to say that the stems end up longer than expected?
Yes, thanks. That is a useful catalogue you linked to, which also covers their measurement systems for other items such as handlebars. I have edited the message of mine above yours to correct the direction of the difference in stem lengths reported in earlier threads, e.g.,
by @StandardPractice in
https://www.lfgss.com/comments/8046256and
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About
Inconsistency in Nitto stem measurement system
Posted by
@Nick_S
Looking into getting a new quill stem from Nitto, I thought I would just measure my old one from a different manufacturer and place an order. It turns out Nitto use two different measurement systems, depending on the model range:
NP(80-120), NPII quill stems: extension is measured at right angles to the section which is inserted into the steerer column, i.e., irrespective of the angle, between the centre of the vertical bolt to an imaginary line extending upwards from the centre of the handlebar insertion.
NP(60,70), NTC, MT quill stems, as well as the UI threadless stems: extension is measured along a centre line of the forward section which follows the angle, between where the line would intersect the centre line of the bolt which tightens the wedge/cone to the centre of the the handlebar insertion.
In all cases the angle is the acute angle (<90 degrees) formed between centre lines drawn through the section inserted into the steerer column and the forward section of the stem.
All this diagrammed in a PDF document available from Nitto's website:
http://nitto-tokyo.sakura.ne.jp/stem-measurement.pdf
In their examples there is a difference of 5mm between the extensions defined by the two measurement systems, but it will vary with the angle of the stem and its dimensions.