Stem length to angle question

[scottcw]

How much difference in reach will there be between a 130mm stem with the following angles:

+17
+7
0
-7
-17

Thanks.

[oldguy00]

http://www.rideyourbike.com/fitkitstemtable.html

[Dustin]

See also Zinn's calculator:

http://www.zinncycles.com/stemFit.aspx

[eddief]

http://forums.thepaceline.net/showthread.php?t=6448&highlight=dummies

[zank]

The calculators given are great tools. Here is another example using an actual bike setup. This is a bit different than the horizontal stem length given by the calculators, as it takes handlebar drop into consideration and gives actual reach changes. I measure reach from the tail of the saddle to the center of the bar. I measure drop as the vertical distance between the top of the saddle and the center of the bars.

I took my road position and frame, and calculated reach and drop for each of the stems you proposed keeping everything else constant (including stem spacers). Here is what I got:

13 cm, 73 degrees - Reach: 82.7 cm, Drop: 10.5 cm
13 cm, 83 degrees - Reach: 82.2 cm, Drop: 8.3 cm
13 cm, 90 degrees - Reach: 81.7 cm, Drop 6.7 cm
13 cm, 97 degrees - Reach: 81.0 cm, Drop: 5.2 cm
13 cm, 107 degrees - Reach: 79.8 cm, Drop: 3.3 cm

So, while the calculator says the horizontal difference between a 13 cm at 73 degrees and one at 107 degrees is 2.2 cm, the actual reach change is 2.9 cm (by my calculations).

I hope this helps.

[pdonk]

For a visual comparison check out

http://www.habcycles.com/fitting.html

[Dave]

Calculating the rise of a stem is pretty simple. Assuming a 73 degree HTA, a -17 (73) degree stem is horizontal.

To find the additional rise due to a greater angle, multiply the 130mm length times the sine of the angle. For example, the -7 (83) stem would have a 10 degree greater rise above horizontal, so 130 x sin10 = 22.5mm.

The 0 (90) degree would be 130 x sin17 = 38mm.
The +7 (97) degree would be 130 x sin24 =53mm.
The +17 (107 degree) would be 130 x sin34 = 73mm.

One of the problems with this type of calculation is that it assumes the center of the stem intersects the center of the stem clamp, which is usually NOT the case. Because of this off-center intersection, when a stem is flipped, the rise won't be as much as calculated. A more common 84/96 stem raises the bars about 2cm when it's flipped.

Don't forget about the stem length change that occurs when it's flipped. A -17 (73) degree stem when flipped, is horizontally about two sizes SHORTER in the flipped position. The more common 80 and 84 degree stem will decrease in length by about one size when flipped.

[scottcw]

Calculating the rise of a stem is pretty simple. Assuming a 73 degree HTA, a -17 (73) degree stem is horizontal.

Good stuff, Dave. Any calculations on my latest post on the thread about saddle setback?