# stem geometry 101, bar height calculations



## acid_rider (Nov 23, 2004)

Hello

I did a search on "stem flip" and literally hundreds of posts returned, so I do know this question has been asked and answered in the past but it would take me a day to find it here so here goes again:

I have +/- 4 degree Deda Newton 31-86 stem of 100mm length. 
If I were to flip the stem over then by how many millimetres exactly would the handlebar height alter? I know the reach will also be affected by about 10mm (refer C-40 post?) but for now I am just interested in bar height. I saw C-40 say once or twice ~20-35mm range for most common stems, but this is a big range and may be for 110mm lenghts, not 100mm which is what I ride. 

Further, I also have a second bike with 100mm long +/- 6 degree stem. What would the bar height difference be for flipped over 6 degree stem? 25mm?

thanks


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## Guest (May 14, 2011)

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

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


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## acid_rider (Nov 23, 2004)

*thanks*

so flipping over a 4 degree 100mm long stem on a 72.0 head-tube-angle frame means ~14 mm change in bar height and ~4-5mm change in bar reach..... 

same calculation for 6 degree, 100mm long, 72.0 HTA is 20mm bar height difference and 7mm bar reach differences

please confirm my calculations as I am really poor when it comes to these things 8^)


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## woodys737 (Dec 31, 2005)

acid_rider said:


> so flipping over a 4 degree 100mm long stem on a 72.0 head-tube-angle frame means ~14 mm change in bar height and ~4-5mm change in bar reach.....
> 
> same calculation for 6 degree, 100mm long, 72.0 HTA is 20mm bar height difference and 7mm bar reach differences
> 
> please confirm my calculations as I am really poor when it comes to these things 8^)


Close enough. For the 100mm stem I'm coming up with 4mm difference in reach and 13mm difference in height.

For the 110mm stem the difference in reach is 7mm and 19mm difference for height.


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## Scooper (Mar 4, 2007)

This chart from Habanero might be helpful.


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## olr1 (Apr 2, 2005)

Um.....

Why not just flip it and see how it feels?

I know it doesn't appeal to the math geek or the science wonk, but it's the best way...


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## C-40 (Feb 4, 2004)

*answer...*

Your stem has angles of 86 and 94 degrees. Subtract an average head tube angle of 73 and you get angles relative to the horizontal of 13 and 21. The rise of the 13 degree angle is sin13 x 100 = 22.5mm. The rise with 21 degrees is sin 21 x 100 =35.8mm. 

The length change is minor. cos13 x 100 = 97.4mm cos21 x 100 = 93.4mm.


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## acid_rider (Nov 23, 2004)

thank you everyone!


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## Kontact (Apr 1, 2011)

acid_rider said:


> Hello
> 
> I did a search on "stem flip" and literally hundreds of posts returned, so I do know this question has been asked and answered in the past but it would take me a day to find it here so here goes again:
> 
> ...


Why would reach move by 10mm? It is maybe half of that.

Those calculators are nice tools. So is ruler and pencil. Just draw it out. You can use a protractor, or just approximate the angle by looking at your stem.


General comment - people worry about this kind of thing way too much. A change in bar tape will affect reach almost as much as flipping a 4 degree stem. And stem makers measure the reach in different ways - you aren't going to know the real reach until you measure the stem itself. What's 5mm between friends, really?


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