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PostPosted: Fri Dec 10, 2010 4:07 pm 
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Joined: Mon Mar 24, 2008 2:00 am
Posts: 49
Location: Conover, North Carolina
I am trying to understand how to interpet the angle of a handlebar stem, and have a hard time with geometry.

On my Colnago EPS, I have a Deda Zero100 stem in 110mm. The specs say it is an 82 degree stem. Looking at the stem, it has almost no rise to it.

My other bike has an FSA OS99 stem, which the specs say is a 6 degree stem.

I'm guessing one measurement is taking head tube angle into consideration??

I want to replace the Deda stem with one that has SLIGHTLY more rise (and it HAS to be an Italian stem) :oops: :roll:

What is it I'm looking for? Can someone explain how stems are measured in Seasame Street level math?


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PostPosted: Fri Dec 10, 2010 6:26 pm 
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Joined: Tue May 27, 2008 8:59 pm
Posts: 196
Location: Boise, Idaho
from sheldon:
Rise

"Rise" refers to the angle of the "extension" part of the stem. This may be referenced either to the steering axis, or to an imaginary perpendicular to the steering axis. Thus, a stem with the extension perpendicular to the quill might be referred to either as a 90 degree stem, or as a 0 degree stem! A traditional "7" shaped road stem might be referred to as a 73 degree stem, or as having a 17 degree negative rise! Caveat emptor!


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PostPosted: Fri Dec 10, 2010 8:09 pm 
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Joined: Sat Aug 29, 2009 4:30 pm
Posts: 1862
For a "standard" 73° Fork angle, a -17° will end up being level with the ground.

So the formula is:

φ = 90 - θ + S

Where φ is final angle above level
θ is you actual fork angle
and S is the stem's angle (can be positive or negative

So, For example, a -6 degree stem on a 72° fork, you will get 90-72-6 = 12 degrees above level.


Except I see the confusion: some manufacturers call a -6° Stem an 84° stem (90-6), so the more common, smaller, angle designation has the 90° already added in.
I think most manufacturers are using the smaller number (Thomson, 3T, VCRC, Easton, etc )


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PostPosted: Mon Dec 13, 2010 4:00 am 
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Joined: Mon Oct 08, 2007 9:51 pm
Posts: 212
Try to find a Deda Zero100-86. This is the same stem you have but with more rise. 4 degrees to be exact. That would put your bars 8mm higher and a couple of mm closer to you.


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PostPosted: Mon Dec 13, 2010 5:24 pm 
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Joined: Mon Mar 24, 2008 2:00 am
Posts: 49
Location: Conover, North Carolina
Thanks for the replies, I think I understand it now. I just ordered a Deda Elementi Deda Zero100 Servizio Corse stem in 86 degree. Hopefully that will raise the bars enough.


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PostPosted: Mon Dec 13, 2010 5:31 pm 
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Joined: Thu Jul 26, 2007 10:24 pm
Posts: 1579
Location: Center of the Universe
http://alex.phred.org/stemchart/Default.aspx

Here is a stem chart that you can use to compare different angles and lengths.

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PostPosted: Thu Dec 16, 2010 9:06 pm 
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Joined: Sun Mar 23, 2008 7:31 pm
Posts: 354
Slowpoke wrote:
I am trying to understand how to interpet the angle of a handlebar stem, and have a hard time with geometry.

On my Colnago EPS, I have a Deda Zero100 stem in 110mm. The specs say it is an 82 degree stem. Looking at the stem, it has almost no rise to it.

My other bike has an FSA OS99 stem, which the specs say is a 6 degree stem.

I'm guessing one measurement is taking head tube angle into consideration??

I want to replace the Deda stem with one that has SLIGHTLY more rise (and it HAS to be an Italian stem) :oops: :roll:

What is it I'm looking for? Can someone explain how stems are measured in Seasame Street level math?


Without studying the answers, it is really simple.

Stems are labeled in two different ways: either (1) the actual angle, or (2) in terms of their difference from 90 degrees. I guess, the numbers are based on mounting the stem on a perpendicular tube, but they have nothing to do with head tube angle on your bike.

In other words, for example, the following stem specs that you might see are equivalent, from lowest to highest rise (and drop):

90 = 0, a right angle'd stem, would be horizontal if the steer tube were perpendicular. This would rise a little from horizontal when mounted on a typical angled head/ steer tube. Would not change if reversed (flipped).

84 = +/-6 would rise or drop 6 degrees if the steer tube were perpendicular. This would rise a little more than the 90/0 if in the "flipped up" position, and would be lower in the flipped down position.

82 = +/-8, would rise or drop 8 degrees if the steer tube were perpendicular. This would rise a little more than the 84/6 if in the "flipped up" position, and would be a little lower in the flipped down position.

76 = +/-14 would rise or drop 14 degrees if the steer tube were perpendicular. A "high rise" for some or "deep drop" for others.

82/8 and 84/6 are probably the most common angles, as you already have seen.

The numbers are +/- because the stem can be installed to angle up or down. To get to the next level of detail, the actual rise from horizontal depends on the head tube angle. Also, if you make significant changes in the rise (or drop), you might need to adjust the length. But a change of +/- 2 degrees would change the reach in terms of a couple mm.

So, for most of our purposes, simply tweaking fit on the frame we have on hand, just look at those numbers and choose a stem that rises (or drops) a little more or less than what you have. Don't over think the geometry.


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PostPosted: Mon Dec 20, 2010 3:59 am 
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Joined: Fri Oct 30, 2009 10:36 pm
Posts: 420
Here is a neat Bike Stem Calculator I found online.

http://www.brightspoke.com/t/bike-stem-calculator.html

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PostPosted: Tue Dec 21, 2010 5:24 pm 
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Joined: Mon Mar 24, 2008 2:00 am
Posts: 49
Location: Conover, North Carolina
Great replies and a great stem calculator. Thanks everyone!


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