Sit Bones Width Measurement and Bike Saddle Selection

How do you choose the right saddle? Bike shops, saddle manufacturers, bloggers, and cycling periodicals have relentlessly tackled this topic for years. While there are resources that offer positive tips, there is one methodology for saddle selection that we’d like to discuss today: sit bones measurement. Is it a good indicator of proper saddle width? While we’d like to remain entirely unbiased, but that’s incredibly unlikely.

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

The Ischial Tuberosity is commonly referred to as the “sit bones,” “sitting bones,” or “sitz bones”(“sitz” literally translates to “seat” in German). In many cases, they are measured to potentially find your optimal saddle width. This seems, at the outset, to be logical as the bony part of the sit bones will experience undue pressure when pressed against a minuscule surface area such as a bike saddle. The cycling industry hypothesis: if your bones are spaced further apart, you’ll require a wider saddle for a luxurious rear-cradling experience.

The Sit Bones Measurement

Many bike companies and manufacturers constructed a plethora of possibilities on how to measure your sit bones. We even use one as a starting point on the BikeFit Edition BiSaddle Instructions. Without purchasing anything, some companies even will send you a kit that’s similar to the home method below. Let’s explore the home and dealer methodologies for sit bone width measurement.

The Cardboard Impression

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

There are similar methods involving paper without the damp posterior result, but now that you feel uncomfortable, you’ve properly ingested this idea.

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

his is certainly not an exhaustive list but many others utilize similar methodology. The process, though, is exactly the same as the home methods provided above. Below is a picture of the sitting position well described in an article by www.cyclingabout.com. The eager cyclist sits at a 90-degree spine position on a more professional looking apparatus, the sit bone impression is apparent on the device, it’s then diligently measured and the match process begins. Width of sit bones + X (Defined as added width by manufacture) = the saddle made for you.

Sit Bones and Cycling Position

Now that we’ve properly defined the sit bones measurement, let’s discuss it. What’s your riding position? Cycling is one of those odd sports where the type of cycling, goals, intensity, and volume will likely affect body position and invariably, your saddle choice. To learn more, take a look at this video from BikeFit founder and master bike fitter, Paul Swift. If you ever have the pleasure of talking to Paul or taking one of his bike fitting courses, this is his baseline level of passion and energy.

While some commuters and leisure cyclists sit at the 90-degree position, the majority of cyclists will have some type of pelvic bend (as Paul mentioned). Consequently, the sit bones would not be your main pressure point or measurement point for potential saddle comfort. Take a look a the position below of three different types of cyclists.

Depending on the discipline, the pelvis is clearly in a different position but the instructions for sit bones measurement for saddle selection focus on a 90-degree spine angle. If the majority of cyclists ride at some type of angle, what part of the pelvis takes the brunt of the pressure in different body positions?

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

In 2015 the Selle Royal Group in collaboration with the German Sport University in Cologne (to make it legit) performed a study(mostly to sell saddles) to discover the optimal shape saddle considering male and female differences and rider position. They broke this down into 3 separate studies: sit bone width, gender differences, and optimal saddle shape. We will summarize the findings, but if you want more information about it, there was an excellent write up constructed by Total Women’s Cycling or on the Scientia site. Below you can see the saddle selection online tool they created based on their 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.
• 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.
• 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:

1. Test the saddle at your local bike shop or bike fitter. Most shops carry multiple saddles and if they don’t offer a way for you to test them, turn around and leave.  You’ll need to know first hand how it feels in your specific riding position.  It just so happens (shameless plug) that the mastermind behind BikeFit created a tool to make this process easy and efficient.

   If you’re a bike shop reading this, the Saddle Changer streamlines the saddle fitting process and helps a customer test multiple saddles in minutes without the time-sucking process of tightening and removing bolts or fiddling with finicky seat posts. If you’re a cyclist reading this, how great would it be to test out 20-30 saddles? Many shops use this awesome tool so feel free to ask them when you call, e-mail, or shadily DM about testing new saddles.

2. Saddle Demo. The Saddle Changer is an amazing tool but riding a saddle for 30 seconds is not the same as an experiencing it for 2 hours. Yes, you can narrow down the choices with indoor testing but to truly discover the best saddle for you requires taking it for a ride. Most cyclists move on the saddle while riding as the road or terrain changes and undulates. As a result, you’ll want to test it in those conditions and in the volume and intensity you experience while regularly riding. Many shops offer a demo program where you can test a saddle for a certain period of time (usually with a deposit) and there are also some manufacturers who now offer a satisfaction guarantee where if you try the saddle and it’s not for you, you can return it. This may take much longer so our suggestion is to visit your local dealer or dealers and ask about their saddle testing programs. Some may even delve into some new technology like adjustable shape and width saddles which provides you with multiple options on a single saddle.

   Unfortunately, if you were hoping there was a correlation between measuring sit bone width and simple saddle selection you were wildly let down by this article. Yet, if you’ve made it this far the truth is revealed. At the end of the day, the goal is to enjoy cycling and an uncomfortable saddle likely will render that mission futile. Do you love your saddle? If you don’t, visit some of your local shops and keep testing until you find the right seat.

-The BikeFit Team (Damon and Paul)

Interested in expanding your knowledge? Bike retailers and shop employees with a QBP account have access to educational resources within the U of Q Training Library. Get started now.