In our previous blog post we learned what our sit bones are and how to measure them. In this post we'll discuss how that measurement is used and why it is only one of several factors that must be considered when choosing a saddle. 

Images above are:

1. anterior (front) view of a female pelvis

2. SQlab Ergowave 612 saddle (top view)

3. Selle Italia Novus Boost EVO TM Superflow (rear view)

4. Ergon SR Pro Men (rear view)

5. Selle Italia Flight Boost TM Superflow (side view)

6. Pro Turnix Performance (side view)

7. Selle Italia SLR Boost TM Superflow (top view)

8. Ergon SR Pro Women (angled view)

In the second image we can see where our sit bones are normally positioned on an SQlab saddle that is the right width for us and set up correctly. Typically, very much to the rear of the saddle and at or close to the widest part of the saddle. On some saddles, such as the SQlab Ergowave range, it is obvious. On others, much less so.

The ideal location of your sit bones may vary slightly depending on saddle design and you may deliberately shift your pelvis forward or backward depending on the terrain you are riding. As a general rule though, a road bike saddle will provide its optimal amount of skeletal support if your sit bones are towards the rear of the saddle when sitting upright.

As we learned in our last post, we begin to roll our pelvis forward onto our ischiopubic rami as we adopt an increasingly aggressive position and lower our torso. As the contour of our pelvis narrows, so too the sides of the saddle taper inward from rear to front in order to match our pelvis. This helps to ensure that our weight is supported at all times on our skeleton rather than on soft and sensitive tissue.

What else do we need to consider when choosing a saddle? What characteristics determine whether a particular style of saddle may be better for you?

For the purpose of this discussion, we'll ignore a fundamental bike fitting principle relating to saddle comfort. That is, the saddle is often not the issue. Your overall position will heavily influence how comfortable any saddle can be and that is a very deep rabbit hole, which we'll explore in another blog post.  Additionally, TT and triathlon saddles are very different beasts and we will discuss them another day. For now we are focusing on road saddles.

Armed with our sit bone width we can begin the search for our optimal saddle. Saddle width is measured at its widest point, but that doesn't necessarily correlate with how much sitting surface is available. This will be affected by how quickly and steeply the sides or wings of the saddle fall away when you look from the centre to the sides. Image 3 is an example of very aggressive roll-off creating an almost bell shape when viewed from the rear.

As a rough guide, with each unique pelvis being more or less sensitive to this, you can take a ruler and lie it flat, left to right, across the widest part of the saddle. Look at it from the rear and any part of the saddle that is greater than 1cm below the ruler probably shouldn't be considered part of the sitting surface. Now that you know the true width of the saddle that your sit bones can rest on you can begin to decide whether the saddle might be right for you.

Now take that ruler and see whether your sit bone width fits inside the true width of the saddle. For example, if you measured your sit bones at 11cm then you'd need at least 11cm of 'sittable' width. Another rough guide is that many people with a mild to moderate amount of anterior, or forward, pelvic tilt will need or prefer approximately 1cm of extra width at either side. This is to accommodate the lack of precision in sit bone measurement and also to allow for some movement on the saddle when riding. 

Not enough extra width and you may feel your pelvis catch or fall off the side of the saddle as you pedal and this can be very uncomfortable. This may also result in too much pressure on soft tissue if you're not supporting the majority of your weight on your skeleton. Too much extra width and your inner thighs may chafe on the side of the saddle, or the back of your thighs may catch on the wings of the saddle as you pedal. This is why you must test ride any saddle you are considering as a static measurement alone will not be sufficient.

How relaxed or aggressive your position is will also affect your ideal saddle width. If you ride with a very aggressive position, you may need or prefer less than the 1cm extra width mentioned above as you will be bearing your weight on a much narrower part of your pelvis.

If you tend to sit almost upright with little or no anterior pelvic tilt when pedalling, you may want up to 2cm or even more extra width. This is to provide sufficient sitting area as you will be resting on the widest part of your pelvis. This may also help to avoid or minimise concentrated pressure points under your sit bones as the greater sitting surface will allow some weight to be borne on the soft tissue of your bum. 

In part two we'll discuss the other factors that must be considered when choosing a saddle. These include curvature left to right, curvature fore/aft, taper rear to front, nose width, nose length and the presence or absence of a pressure relief channel or cut-out.