Saddle height physionumerology

From a Dahon, to a Birdy, and finally through a Brompton list I follow comes the following tip that seems to work spookily well. See, my wife and I share a few bikes, and as I’m taller we have to re-set the saddle heights several times a week. Usually we eyeball it well enough, but too often not well enough. This should fix that:

A local frame builder (who is also a veteran racer) once showed me how the European race teams deal with quick fitting bikes in case of a mechanical problem — It seems that for most or all folks, the distance from the arm pit to the tip of the index finger is the same as the correct distance from the top of the saddle to the center of the bottom bracket. Now I know there may be slight errors, especially since the crank arm length can vary from 165 to 175 (1/2 inch), but I have tried this myself, and it works. What you do is put the seat in the crotch of your arm pit, and adjust the seat post until your finger tip comfortably rests in the middle of the crank bolt. It may not be perfect, but it will be within 1/2 an inch, and probably more like within 1/4 of an inch.

I can probably forget now that my saddles should be 77cm from BB center. They should be “arm’s length.” It has that primal, biblical, cubit-and-span-and-the-king’s-foot thing going on. Does it work for you?

12 thoughts on “Saddle height physionumerology”

  • Matt Liggett

    Pretty close. I keep the saddle on my Cross-Check about a quarter inch lower.


  • Spence

    Wow! That is so cool! Deb and I have been sharing the stoked xtracycle recently — great tip!

  • Bill Manewal

    Works for me, within the +/- 0.5″ tolerances of my flesh smooshing around on different points of a Brooks B67.

    Now, along with my arm span being my height, my hand span being 10″, the first joint of my little finger being 1″, and the width of my little fingernail being 1 cm., I have another useful purpose for my analog body.

  • Dave

    “from the top of the saddle to the center of the bottom bracket”.

    What is “the center of the bottom bracket”? I’d love to employ this method, but I’m unsure exactly what I’m measuring between!

  • Todd

    Dave, it’s the middle of the circle described by your pedals, on the crank. There’s generally a bolt there, fixing the cranks to the bottom bracket spindle.

  • Magnus

    Awesome! I have a folding bike and have been wondering how to set the seat height every time I unfold.. I find the arms length method to be very close, though a little shorter than I prefer.

    If I place my fist on the seat, the height is correct when my thumb hits the very top of my hip-bone. (Obviously this method will depend on the height of the bottom bracket from the ground, among other things..)

  • Bill Manewal

    Magnus – I have a Hon folder whose seatpost has a hole drilled at the proper height. After unfolding, I insert a pin with a spring-loaded ball on the end into the hole and this keeps the post from sliding down into the seat tube. The pin is tethered to the frame with a zip tie. Works well.

  • Karl

    it’s pretty close for me. I can make it work better or worse by sliding my armpit along the saddle a ways (seat tubes are at an angle with the top of the saddle), but if I were to need to set the seat height in the future, this would get me pretty close. I bet the saddle would end up being a shade high, if anything.

  • Andrew Janjigian
    Andrew Janjigian July 28, 2006 at 9:20 am

    Yep. Comes to within 1/2″ for me. Spooky. I guess what that means is that most peoples legs are just slightly longer than their arm inseams.


  • Bartosz

    I know this little trick since the early days of my biking. My father told me about it, and I thought it’s simply common knowledge :)

  • fred

    I think you come from a country where bicycling might be treated as something more useful than a toy. Unfortunately, in the
    United States, too many families consider bicycling as second-rate and do not educate their youngsters in proper operation
    and service, among other things. I am envious of your upbringing in that respect, as I have had to learn all that I know
    in other ways. Some of those ways include making mistakes and learning from them :-)

  • Shane

    Used this method all the time when riding for Pedal Express and have shared with a lot of folks. I think some of them even us it. Works pretty good.

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