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)
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.