# Stem Flip Drop Calculation

I have a 80mm +/- 6* stem. If I flip it over from current “up” position, to “down” what is the effective drop i am getting? I know this is basic grade 9nmath but for the life of me my monday brain cannot figure it out.

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http://yojimg.net/bike/web_tools/stem.php

You can fine tune the head tube angle for more accuracy if yours differs from this example.

This assumes the same stem flipped, and installed with the same spacers under the stem.
You can tweak that by altering the “Height” value for either stem taller or shorter in accordance with spacer swaps to really fine tooth comb the deltas.

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You have a triangle, two sides are 80mm, one is unknown, but opposite a 12 degree angle or 0.20944 radians. You apply the law of cosines to solve for the unknown side. The exercise is left for the reader. But, a calculator google pops up claims 16.72 mm.

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I asked CoPilot this question. I had to modify it a bit, so here’s what I came up with

##### Sent by you:

I have a 80mm stem. If I flip it over from current + 6 degrees position, to a - 6 degrees position what is the effective drop i am getting.

Here’s what CoPilot responded with:

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Just a note on the two calculations above, neither seems to take Head Tube Angle into account. The declined nature of the steerer yields slightly different values to what seem to be pure vertical calculations above. Darn near rounding error deltas even at 73* HTA, but worth noting at least, in addition to the Reach delta that comes from the HTA as well (and lacking in the calcs).

All the more reason to use a premade stem calculator like I linked since it catches that angle and gives options for stack height and spacer considerations. For as simple as it is, I use it in a majority of my bike fits.

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Ha its funny I had done the same but I was second guessing the numbers a little bit due to the HA piece that @mcneese.chad had said.
Overall it doesn’t make that much of a difference and does get me close into the ballpark of what i was looking to understand.

thanks,

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