Actual length Zipp Service Course SL stem

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Dr.Dos
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Joined: Sat Mar 27, 2004 11:00 pm

by Dr.Dos

A friends' Zipp Service Course SL 120mm/-17° stem is closer 130mm. I'm in the market for a 130mm/-17° Zipp Service Course SL, does somebody own one and would measure the actual length?

Center Ahead-bolt to center of bars or any info regarding general accuracy of Zipp stems would be fine.

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Dr.Dos
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by Dr.Dos

To answer my own question: 130mm/17° are more like 138mm measured on top, center to center. Finally I get my 15cm drop to saddle and long reach. Exceptionally stiff, too. I hate the torx bolts, though - uncalled for.

by Weenie


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Darceking
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by Darceking

I know the Bars are very similar. My Zipp SL80 bars measured 45.5 C-C and they are meant to be 44cm C-C . I ended up taking them off and installed 3T ErgoNova 42 C-C. Much nicer.

3Pio
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Joined: Wed Mar 09, 2016 7:13 pm

by 3Pio

Darceking wrote:I know the Bars are very similar. My Zipp SL80 bars measured 45.5 C-C and they are meant to be 44cm C-C . I ended up taking them off and installed 3T ErgoNova 42 C-C. Much nicer.



Hmm.. How do u measure them? My ZIPP Service Course SL80 handlebars are 42cm center-center in the hoods, and 44cm center-center in the drops. Exactly as specs. And can u please tell me what stem do u use, and how stiff were ur ZIPP Bars?

Fiery
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Joined: Sat Mar 16, 2013 9:21 am

by Fiery

Stems are not measured from the top, but along the actual center line of the stem. If you measure from the top, you will normally get a longer than nominal length, especially with a -17. In the diagram below, stem length is marked as "extension".

Image

The only exception that I know of is 3T, who measure what is marked as "reach" on the diagram as the nominal stem length.

Shrike
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Joined: Fri Jun 03, 2016 5:08 pm

by Shrike

Have one of those -17 120mm's for sale at the moment, barely touched too.

Measures bang on 120mm if measuring it right.

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Dr.Dos
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Joined: Sat Mar 27, 2004 11:00 pm

by Dr.Dos

Fiery wrote:Stems are not measured from the top, but along the actual center line of the stem. If you measure from the top, you will normally get a longer than nominal length, especially with a -17. In the diagram below, stem length is marked as "extension".

Image

The only exception that I know of is 3T, who measure what is marked as "reach" on the diagram as the nominal stem length.

As you never know who (including OEMs) measures what it is best to ask and give details on how to measure (without taking things apart). And a -17° stem is about the easiest to measure and compare as readings will be the same center/center vs. center/center/center/center, hence I was keen enough to ask here.

But thanks for the lesson regardless, I need to be tought once in a while. That's why I frequent the interwebz :)

Fiery
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Joined: Sat Mar 16, 2013 9:21 am

by Fiery

To the contrary, the further away from 0 a stem is, the bigger the differences will be between different measuring methods. This is exactly why you get 138 mm when measuring a 130 mm -17 stem from the top. Flip it over and measure from the top again, and you will get something like 122 mm.

What does bring some more confusion is that tolerances for forged stems are not all that tight. You may have noticed Sky team uses stems measured to the millimeter (example). It is highly unlikely Shimano actually makes stems in one millimeter increments specially for them; what happens instead is that they accurately measure and label stems that would otherwise be rounded up or down to the nearest centimeter and sold as such.

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Dr.Dos
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Joined: Sat Mar 27, 2004 11:00 pm

by Dr.Dos

No, -17° is more or less parallel to the ground. Hence center to center will always be center to center, regardless if measured on top or virtual centers of bar and shaft.

On a -10° stem, it will be a tiny fraction less ((ca. 16mm bar radius plus ca. 4 mm material) * cosd(7) * 2), when measured on top compared to measured in the virtual centers.

I am not talking about effective reach and I never was, that's why I provided info of how I would like to have it measured. And now please, stop wasting my time as I already have the stem and I'm happy with it because it effectively measures longer than advertised. And if you think, I have no idea what I'm talking about, yup you're right and have no idea.

Fiery
Posts: 420
Joined: Sat Mar 16, 2013 9:21 am

by Fiery

The problem is that the center line of the steerer is not perpendicular to the ground. It's easier to demonstrate with a picture (it's a bit messy since I reused the diagram, but I hope it is clear enough):

Image

The center measurement is what is normally declared as the nominal stem length. This is clearly shorter than what you get when you measure from the center of the steerer to the center of the handlebar along the top of the stem.

I'm really sorry if you feel this as a personal attack. If it's a waste of your time to read a conflicting opinion, I most certainly won't be insulted if you ignore what I write. I will still write it though, if not for you then for someone else who might be confused about stem lengths and different ways people measure them.

by Weenie


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