Trying to understand stem angles

Questions about bike hire abroad and everything light bike related. No off-topic chat please

Moderator: Moderator Team

Post Reply
Slowpoke
Posts: 49
Joined: Mon Mar 24, 2008 2:00 am
Location: Conover, North Carolina

by Slowpoke

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?

by Weenie


dmotoguy
Posts: 196
Joined: Tue May 27, 2008 8:59 pm
Location: Boise, Idaho
Contact:

by dmotoguy

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!

User avatar
Rick
Posts: 2018
Joined: Sat Aug 29, 2009 4:30 pm

by Rick

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 )

Wester-Ross
Posts: 213
Joined: Mon Oct 08, 2007 9:51 pm

by Wester-Ross

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.

Slowpoke
Posts: 49
Joined: Mon Mar 24, 2008 2:00 am
Location: Conover, North Carolina

by Slowpoke

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.

Gregorio
Posts: 1582
Joined: Thu Jul 26, 2007 10:24 pm
Location: Center of the Universe

by Gregorio

http://alex.phred.org/stemchart/Default.aspx

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

Camilo
Posts: 361
Joined: Sun Mar 23, 2008 7:31 pm

by Camilo

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.

fogman
Posts: 774
Joined: Fri Oct 30, 2009 10:36 pm

by fogman

Here is a neat Bike Stem Calculator I found online.

http://www.brightspoke.com/t/bike-stem-calculator.html
It's all downhill from here, except for the uphills.

by Weenie


Slowpoke
Posts: 49
Joined: Mon Mar 24, 2008 2:00 am
Location: Conover, North Carolina

by Slowpoke

Great replies and a great stem calculator. Thanks everyone!

Post Reply
  • Similar Topics
    Replies
    Views
    Last post