The Sit Bones, “Sitz Bones” Sitting Bones or Ischial Tuberosity

The Sit Bones Measurement

The Home Measurement Methods

This method involves sitting upright on a piece of corrugated cardboard for a designated period of time.  After that point, you’ll mark the main impressions of the sit bones, find the center point of the two impressions, and finally measure the distance between the two points with a ruler or tape measure.

The Wet Measurement or “Damp Spot” Method

After measuring the sit bones distance, most companies provide either a “finder” online system on a chart where your measured sit bones width correlates to certain saddles.  Many suggest adding about 20mm, as signified by the Road Bike Bros above, which would then land you on the ideal saddle.  For example, if your sit bones measured 130mm, you add 20mm and voila, a 150mm saddle width will fit perfectly!  It’s interesting to note that the Road Bike Bro measured 110mm, added 20mm, but choose a 145mm width saddle which in his words, “provides more support and I find it more comfortable.”

Some selection tools will also incorporate riding style, but let’s not get ahead of ourselves.  Before we move on to the effectiveness, take a moment to observe the sit bone measurement methods proposed by some of the powerhouses in the cycling industry.

The Industry Methods: Giant Peanuts and Gel Pads

Sit Bones and Cycling Position

www.bisaddle.com

The two diagrams above provide a much clearer picture of pelvic position and which bones receive the most pressure depending on the amount of rotation or position of the rider.  We did not quantify this to a degree of angle as this is rider dependent.  Yet, our friends at BiSaddle (image to the upper right) pointed out that the pubic Rami may be a much more common pressure point measurement vs. the sit bones.  If you are a triathlete, racer or a more “aggressive” positioned rider, measuring your sit bones for saddle width provides an improper account of what’s actually in contact with the saddle.  This does not incorporate the fact that in a more aggressive position, you’re also encountering more sensitive organs and tissue beyond the bones of the pelvis.

Industry Sit Bone Research

• Ischial Bone Study (sit bone width):  Selle found a wide variation of sit bone widths from their 240 participants and subsequently created 3 saddle widths based on the averages in the study.  The width was measured at the 90 degree spine angle and they created another device (seen above with the teal gel pad) to assign a saddle based on sit bone width.  The most interesting part of this study was this precious gem mentioned in their research, “Ischial (sit bone) distance varies according to riding position due to the v-shape pelvic anatomy.  In the more inclined spine angle, the distance will become shorter as the contact points move from the seat bones toward the pubic bones.”  Result: if you ride with a 90 degree spine angle, then the sit bone measurement may be somewhat accurate (more on this later).  If you ride in any other position(most cyclists) it’s likely that the contact point will move forward away from your sit bones,  which, they do not mention, renders sit bone measurement (in the 90 degree form) for most enthusiast and competitive cyclists completely irrelevant.
• Gender and Shape Study:  Although this does not connect specifically with sit bone measurement, it does impact our point about spine angle. 66 participants were tested using specific pressure mapping with 64 different sensors at the 30, 45, and 60 degree angle.
  • Selle assumed that the pelvic position on the 60 and 90-degree would have the same result.  This is likely debatable depending on the rider but certainly, individual preference and riding style will impact saddle comfort.  Therefore, when considering an incredibly sensitive decision such as the saddle, why make a conclusion without doing the testing? Selle already invested the money so it would have been helpful to test and rule it out.
  • The differences between male and female average and maximum pressure was minimal at the 60 and 45 degree angle but at the 30 degree angle it was significant, which they concluded was due to the anatomical differences between male and female.  Considering that Selle’s line of the Scientia is based on the upright rider vs. the road, gravel, cross, mountain, tri…etc. rider, they clearly avoided the area where there is significant sensitivity and variance among males and females.  We are not inside the board room of intricate decisions of the Selle Royal juggernaut, but if they found significantly reduced pressure and gender differences at a higher spine angle, it makes sense that they would potentially avoid saddle selection that would disprove the sit bone width method.

How to Find the Right Bike Saddle

Without being redundant (which means this is redundant), it’s clear that unless you are riding upright on your saddle, a sit bone width measurement and saddle selector tool based on that idea is likely irrelevant based on your spine angle, pelvic pressure, gender, and/or riding style. Yet, let’s take this a step further.  There’s no guarantee that a sit bone measurement based on the 90-degree riding position will provide you with a comfortable saddle.  There could be a comfort issue based on the external material of the saddle, the density, the type of foam used, your weight or the clothing you wear (we won’t go into this one here).  Consequently, the only way to truly find your perfect saddle is to personally test the saddle.  Granted it was helpful of Selle to embark on research regarding shape, gender, and body position’s impact on saddle selection but there’s no online bike saddle match or finder that will tell you how it feels.  There’s another company that offers a selection tool based on your flexibility but regardless of how or if you can touch your toes, that doesn’t tell you how the saddle feels after a 60 mile gravel ride.

To continue with the concern about the “sit” measurement, a static measuring process does not assure comfort in a dynamic sport.  How often do you sit on the saddle without pedaling while riding?  For most disciplines, you pedal and pedal often.  As a result, your comfort on the saddle is based on how you feel pedaling vs. the static measure of your seat area.  Even if you were bent in the proper pelvic position to measure pressure, that pressure would likely change based on your pedal stroke.

Here are the BikeFit suggestions to finding the perfect saddle for you: