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Math question about stem length and angle

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Math question about stem length and angle

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Old 08-12-10 | 05:47 AM
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Math question about stem length and angle

Was fitted recently at LBS, among other adjustments, moved saddle forward as I was pretty far back behind the center of the cranks. All the adjustments feel better to me after 2 rides, but I now feel a bit compressed as I am now closer to the bars, especially when on the hoods.

I am thinking that I may need to get a longer stem or one with more of an angle. I am currently using a 90mm 84 degree stem. Obviously going to a 100mm gives me 10 more millimeters of reach.

Does anyone know what the effect of going from a 90mm 84 degree stem to a 90mm 80 degree stem would add to reach?

Thanks.
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Old 08-12-10 | 06:19 AM
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google is your friend
https://www.habcycles.com/fitting.html
https://www.brightspoke.com/t/bike-stem-calculator.html
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Old 08-12-10 | 07:23 AM
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Still about 10mm. The angle effect of 4 degrees will have a minor effect on length, and a bigger effect on the bar height. The 80 degree stem drops the bars about 5mm.

To figure all of this, assume a 73 degree head tube angle. The stem angle is 84-73 = 11 (relative to the ground).

The horizontal length of the stem would be cos11 x 90 = 88.3. The height would be sin11 x 90 = 17.2. With an 80 degrees stem it's cos7 x 100 = 99.3 and sin7 x 100 = 12.2. That makes the length difference 11mm and the height change 5mm.
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Old 08-12-10 | 05:30 PM
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https://alex.phred.org/stemchart/Default.aspx
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Old 08-12-10 | 06:52 PM
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Thanks to all for helping out. Especially DaveSSS for the trig lesson, no wonder I'm in the field of law rather than an engineer...
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Old 08-13-10 | 09:21 PM
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Wow. Fantastic stem calculators on those links above. Thank you. I had no idea something like this existed. Sure does make figuring out which replacement length/angle stem to get much easier.
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