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 Home Measurement Methods

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

This 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.

How Often do You Stop Pedaling?

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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.
  • 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, or your weight.  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)

How to Fit a Triathlon or Time Trial/TT Bike Part 2: The Pelvis/Saddle Fitting

saddle

TT/Tri Fitting Part 2:  

The Pelvis/Saddle Fitting

Saddle Selection

Rarely do bicycle fitting articles mention saddle selection. Reality: this should be the first step before making any adjustment to the seat height, tilt, or fore/aft position. Riding with the wrong saddle can compromise your comfort and ideal cycling position dramatically.
As simple as it sounds, the best way to find the most comfortable bike seat is to sit on it. The problem lies in the fact that switching saddles is both time-consuming and difficult.  Changing a saddle can take up to 15 minutes per seat which means most people select a seat by pressing a finger into it to test its firmness or softness. Another option is simply choosing a saddle based on advertisements. Some saddle manufacturers have done a nice job with their design and a fabulous job with their marketing.  Unfortunately, this still doesn’t help you procure the ideal saddle.  Fortunately, we solved this problem. At BikeFit we built a saddle fitting tool called the SwitchIt™ that quickly and easily allows you to test as many saddles as you’d like by sitting on them:

Not all shops carry the SwitchIt so you’ll need to ask for it or find another bike shop that does. When you find a shop with a SwitchIt, try to set the position on their sizing bike or stationary bike that has it mounted it to a similar position as your triathlon bike.  Try as many saddles as you like until you find the one that fits best before you make your purchase. It may come as a surprise that the seat you currently ride is not the best saddle for you. Let your tush be the judge!

Saddle Selection Misnomer

Beware of other ways a bicycle dealer may guide you with saddle fitting and saddle choices. Some bike shops may have you sit on a device that takes an impression of the width of your sit bones. If this device actually works, the best information it “suggests” is how wide or narrow of a saddle you “might” like. Unfortunately, we can share with you story after story where this device does not provide information for a comfortable saddle choice.
Illustrations 4 – As you can see sitting on bike is not like sitting on a box
As mentioned, the incorrect saddle can compromise your position on the bike and, of course, feel uncomfortable.
As you try to find the right saddle, keep an open mind. Some shops may start you down a saddle choice path by pointing out saddles designed for a triathlon or for men or women specifically. However, some triathletes find a road saddle more comfortable and some men may find women’s specific saddles more comfortable or the other way around. Either way, please be ready and willing to try ALL kinds of saddles.

Saddle Cutouts

Are seats with a cutout good? It seems that in the past some seat manufacturers added a cutout to make up for their less-than-ideal saddle design. Many saddles did not offer the ideal support in the right area. A good-fitting saddle may not need a cutout if the support is in the ideal area for you. Where is the ideal area? It varies from person to person.  In general, for most of us (male or female) it means not too much pressure in the front or in the center of the saddle.  For some, sitting slightly off to one side may be the answer.  Bike fitter extraordinaire John Cobb often recommends positioning the nose of the saddle to one side.

Illustration 5– tip of saddle rotated to the right. More information can be found about Cobb Saddles.

Ultimately a cutout seat may prove the most comfortable, but don’t discount those saddles without a cutout before trying them first. You may surprise yourself as to which feels best.

Saddle Tilt

Is a level saddle the best position for you? It may be ideal for some but probably not for every triathlete. Numerous people tilt the saddle nose down thinking it will increase comfort. If you must tilt the nose down more than a few degrees, you may not have the right saddle and/or the overall bike fit is likely too far off. Too much downward tilt usually results in your pelvis sliding forward. This leads to hand, elbow, forearm, triceps and shoulder discomfort or pain. You may find yourself pushing your pelvis back from the bars several times in a ride. Some people will also feel like they are pedaling more with the tops of their quads (just above the knee).  While not as common, some saddles feel better with a slightly upward tilting nose. The best adjustment for your saddle really depends on you and on the saddle itself.  So don’t get hung up by someone saying it is “supposed to level” or “tilt” this way or that way.  Rather, adjust to what feels best.
BikeFit App Saddle Tilt Tool

The BikeFit App for iPad and iPhone saddle tilt tool.

Saddle Height

The starting point for most do-it-yourself bike fits is typically saddle height. Sit on the saddle with one leg hanging free and your pelvis level—not one hip tilted higher or lower. Your hanging leg’s heel should just scrape or touch the pedal when the pedal is at the very bottom (6 o’clock). Once you slide your foot back to bring the ball of your foot to the center of the pedal you should have a slight bend in your knee.

 
Illustration 6 – Heel Scrape

In our experience, the properly bent knee resides between 27 and 37 degrees of flexion from a straight leg. Typically, most people have greater than 30 degrees of knee bend at the bottom of the pedal stroke. The Empfield – F.I.S.T guide suggests an even lower saddle height range.  Collectively we feel that you will almost never see someone needing to be taller than our ranges. Occasionally you might rarely see someone lower. If your hips rock a little when you pedal, lower the saddle a couple millimeters and test again. Repeat as necessary until you eliminate this rocking. You may be someone that just rocks.  Don’t feel like the Lone Ranger; you are not alone. At this point, you may want to consider shorter cranks. If you are on a fit bike with adjustable cranks, shorten them and observe the changes.
While there are formulas that take into account your inseam measurement, they generally do not produce any better result than this heel scrape method.
We recommend using a Goniometer to accurately measure knee bend. Take a look at the goniometer checking knee flexion or the bend in the knee at the bottom of the stroke:


Illustrations 7a & 7b – Goniometer measurement and proper knee angle

Saddle Height Accuracy

Can saddle height be set to the exact millimeter?  Saddle height is never the same even for the same person. What do we mean by this? What happens if they wear a different pair of cycling shorts? That precise measurement is now not so precise. Does the “millimeter measurement” account for the wear and tear of a saddle that has been ridden for a long period of time? What if the rider feels tight one day, rested the next day, or they wear additional clothing to accommodate for cold weather? The list is nearly endless. Bottom line: the millimeter adjustment is not as important as you might believe.

Saddle Fore/Aft Position

For years common thinking for saddle fore-aft positioning was determined by the knee over pedal spindle (KOPS) positioning. The KOPS fit process: place one foot forward (3 o’clock) with your crank arms parallel to the ground and then ensure that the forward knee cap is just over the center of the pedal (see picture below). For some riders, this method will work well enough for a road or mountain bike fit but that is a “maybe” at best.

 
Illustration 8 – Knee over Pedal Spindle alignment

Many people use a plumb bob for this measurement (we did at one time). We found a laser or the BikeFit Pro App to be easier and far more precise. While the right leg in the photo above is closest, the rider can spin the other leg forward and check the fore/aft on the far leg as well without moving the laser. We also refer to this as a “hands-free” technique.  With a laser, the fitter is able to make an adjustment or simply step back and take a look.  This is not possible with a weighted string hanging from the knee. Today we use this more to see if one knee is further forward than the other but NOT to check the actual saddle fore-aft position (especially on a triathlon bike fit).

Unlike road or mountain bikes, KOPS is NOT a starting point for triathlon bike fit. The modern method we subscribe to is a modified (but fairly close) Dan Empfield or Slowtwich approach. As mentioned above, my early influences come separate of Dan, having lived at the Olympic Training Center (OTC) in Colorado Springs when funny bikes were first being made.  I was also influenced by working with aerodynamic guru John Cobb. We put a lot of John’s information in our first bicycle fitting manual, possibly the first fitting manual on tri bike fit.  It is not that tri bike fitting was not talked about, but finding a manual for one was next to impossible.


Illustration 9 – A bike that may have been used in the 1984 Olympics – notice the small wheels

UCI Exceptions: Saddle Fore-Aft

There is an exception to the fore-aft saddle position for time trial bike fitting or for any bike that needs to be UCI legal. Because of this, it is actually easier to fit a time trial bike than it is a triathlon bike–one of the driving aspects or fit parameters is automatically set for you. We are not saying this is a good thing but rather an easier thing.

Illustration 10 – saddle set at 5cm behind the center of the BB

For USAC or UCI races or time trials, set the saddle height and put the nose of the saddle 5cm behind the BB and “Voila” you have your seat position for a time-trial bike. There are other parameters to follow. Just to make things more complicated, the UCI has a jig and your bike needs to be set up within the guideline of this jig (or template).  This resembles a template for a stock car.

To see what this jig looks like, here is a bike that is set up illegally for UCI/USAC racing.

Illustration 11 – Saddle too far forward for UCI and USAC racing.

jig saddle fitting
Illustration 12 – UCI bike requirements.

Additionally, not shown in this illustration are several angles and positions of the cyclist on the bike that must adhere to UCI guidelines.

Learn More About Time Trial/Triathlon Fitting

If you are interested in learning more, please see our next Time Trial/Triathlon Fitting Article: Part 3: Upper Body Positioning.

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