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Old 01-19-14, 11:41 AM   #1
rpenmanparker 
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Different stem length on top and bottom...DUH!

I hope I'm not the only one who has ever noticed this, but I really feel foolish. I was looking at my new 110 mm stem and thinking how long it looks. So I measured the length on the top of the stem from the space between the joint where the face clamps on to the center of the top cap bolt. Sure enough I got 116 mm. WTH? Then I realized (first time) that the tilt in the stem makes the other side shorter. Sure enough on the bottom it is correct, 110 mm. Never thought about it before. I always knew the reach of the stem was different turned one way than the other, but it never occurred to me the slant in the head tube translated into the actual stem measurement being different from one top to bottom. Despite many roadies' preference for the aesthetics of the stem flipped down, it is actually when it is flipped up that the "top" of the stem, the more readily accessible side, measures the nominal length. At least on FSA. Go figure.

I guess the measurement from the true center of one clamp to the other is half way in between the two extremes, 113 mm on this 110.

Anyone have a different result with another brand?
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Old 01-19-14, 11:56 AM   #2
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the stem length is from Centers.. axis of the steering tube, to the center line of the handlebar,

through the center of the stem .. that is how they are sold.

if the stem is 90 degrees from the steerer clamp, then Both top and bottom will , externally be the same ..

if it's mitered at an angle other than that , of course one side will be different from the other ..


NB: Shopping in person has many advantages ..

hold it in your hands and try before you buy , just one of them

Last edited by fietsbob; 01-19-14 at 01:52 PM.
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Old 01-19-14, 01:02 PM   #3
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Originally Posted by fietsbob View Post
the stem length is from Centers.. axis of the steering tube, to the center line of the handlebar,

through the center of the stem .. that is how they are sold.

if the stem is 90 degrees from the steerer clamp, then Both top and bottom will , externally be the same ..

if it's mitered at an angle other than that , of course one side will be different from the other ..
Thanks, that makes sense. But my measurement says it is through center of diameter of each clamp circle, but not the center from top to bottom. I get the nominal measurement on the short side, not dead center. I could be mistaken, but it was pretty clear. As I say, at least for FSA. Anyone else want to try their hand at this?
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Old 01-19-14, 01:49 PM   #4
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The measurement is along the axis of the stem from where it intersects the steerer and where it intersects the bars. This is neither the top nor the bottom of where it clamps to the steerer, and not even the middle between those two, but it's close to the middle. Of course the salient measurements are not the length and angle, but how far above the bottom of the steerer clamp the bars are and how far the bars are in front of the steerer's axis. What path the stem takes between these two points is immaterial.
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Old 01-19-14, 01:54 PM   #5
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Your measurement is not as the Manufacturers use to tool up to make parts ..

If you want predictability , use the Industry Standards..

head tube angle & the stem angle and length combine to be a diagonal line

between run and rise ..

Plot our where you want the handlebars to be then work backwards,

to the parts dimensions you need to get there..

Last edited by fietsbob; 01-19-14 at 02:14 PM.
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Old 01-19-14, 04:50 PM   #6
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I measured mine with a taylor's tape by wrapping around and around, and it came to almost 1/2 meter...
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Old 01-19-14, 05:15 PM   #7
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Rest assured that the stem is on spec. They don't tool up to make thousands and get it wrong.

So we're all on the same page. the measurement is center to center, down the center of the extension.

I'm sure that if you measure correctly, you'll get the right answer.
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Old 01-19-14, 05:30 PM   #8
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Originally Posted by rpenmanparker View Post
I hope I'm not the only one who has ever noticed this, but I really feel foolish
The facts suggest "you are" and "you should"
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Old 01-19-14, 09:29 PM   #9
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Since you have the right answer already, at least for threadless stems; I'll throw in the exception to the rule - quill stems. Most quill stem manufacturers measured length basically the same as the threadless standard. Cinelli (and possibly others I haven't run across) measure the length perpendicular to the quill. What this means in real life, though, is that if you measure ~115mm down the top of the stem, that's Cinelli's size 110. This ~5mm adjustment works for the road stems - I've never had a track one in my hands.
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