Stem Calculator  

A bike that fits properly is one of life's high points

Note: The above method of measuring stems is only one of a plethora of methods employed - but is probably the most popular one currently.  Some manufacturers measure stems in "degrees above horizontal" (common on road bikes, and assuming ~72-3 degree head tube), "degrees from 90 degrees", etc.  If in doubt, print out the chart, and use it to guesstimate your stem's "degrees above horizontal" value by aligning the bottom of the chart with a horizontal surface and sighting the stem extension against the extension lines on the chart. You'll usually be pretty close in estimating your head tube angle at 73 degrees (road) or 71 degrees (MTB).  So, to arrive at "stem angle", add the head tube angle to the "extension angle" from the chart and you'll have a number that most bike shops can use.  

To calculate the effect of raising a stem, add 0.96cm of rise for every 1.0cm of quill or steer tube you expose, and subtract 0.30cm of reach.  


If you want to calculate the new stem you need without doing any math, the following table should help.

I've plotted the chart based on a 72 degree head tube angle, so it's not going to be off by more than 1-2 degree for 95% of the bikes out there.  This really won't affect the outcome of the results enough to matter.

I've labeled the "commonly available stem angle options" on the lines below, so really all you need to do to calculate your new stem is to plot your current stem (assuming it's a -17, -6, +0. +6. +20, +30, or +40 degree stem), and then move up/down/back/forth from that point to your desired handlebar position, and read off the "nearest available stem".  

For example, let's say you are currently running a 9cm, +6 degree (aka "96 degree") stem, and you have decided you want to raise your bars 2" / 5cm higher than they currently are.  First, follow the 96 / +6 degree line out to the 9cm point, which represents where your bars are now.  Then count up five lines (each is 1cm) from that position.  You'll end up very close to the 12cm point on the 120 / + 30 degree line, which means that if you swap out your 96 degree, 9cm stem for a 120 degree, 12cm stem (and leave the spacers as they are), your bars will end up about 5cm / 2" higher.

A similar approach can be used for any combination of moving the bars (higher / lower / longer reach / shorter reach).


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