My wife and went to our LBS today and had our sit bones measured and only cost a few minutes of our time. A neat little device that worked well and gave us more accurate information helping us understand our correct sit bone width if and when we order new bike saddles.

Here is the SB measurement pad, pretty cool. The yellow lines indicate the approximate center of each sit bone. I measured a medium at 138mm. FWIW...

Next time someone calls me a Clyde..

"I'm not fat! I just have big sit bones!"

I'm starting to see those devices in more and more bike shops these days. I'm sure it helps them look more professional when suggesting a saddle.

I don't want to be there when they ask my wife to measure her assh

What saddles did you get?

lol

Yep the op is a REAL fat ass if they are true. lol

Unfortunately, cyclists largely do not sit on the "sit bones" - the ischial tuberosity. We sit on those when upright in a chair, but leaning forward on a bicycle we sit somewhere on the narrower ischium or ramus - the rocker shaped bones going from the tuberosities to the pubis.

Specialized has popularized sit bone measuring, and then matching that number to a saddle width. But bone numbers are indirect. The outer 1/2 - 1" of saddle doesn't do anything - it just completes the shape. So that width is variable in its significance to sitting area.


So while some saddle brands may have a formula for matching sit bones to saddle widths, the overall scheme is like measuring peoples ankles to sell them shoes that are measured at the outer width of the sole, rather than measuring feet and the last.


The only really good way of finding a saddle is to sit on them. I have customers with sit bone widths exceeding the total width of the saddle. But they aren't sitting on those bones, and the ones they are sitting on fit the saddle perfectly.

Yes neighbor it was a typo, and corrected.

Does that mean the saddle thing should be custom made? Imagine, you bring in your bike. Put it on a trainer and the saddle is replaced with a high tech saddle that begins to use sensors to locate the pressure points at various riding positions.

You can do it at home with a big piece of aluminum foil on the carpet floor that you sit on and a tape measure.

And uh, yes, you do sit on your sitbones. That's kind of why they make like small indentations in your saddle after awhile lol

As I tell my wife - fat bottom girls make my rocking world go round! Skinny gals don’t look half as good as a good rump on a bike.

I think Kontact is saying that when you lean forward to the hoods or drops, your bone contact points with the saddle are narrower than they are when you sit straight up. For some silly reason (probably due to doctors) we have different names for the bone in those two conditions. Are they all sit bones? Well, yes, effectively they are.

RonH,
We decided to give these saddles a try based on our sit bone measurements and not wanting a thick layer of foam. Naturally saddle comfort- what works for one may not work for another. That said, the Trek 30 day return policy certainly helps a buying decision as we don’t care to own a box of saddles that for whatever reason did not work out. These saddles will be mounted on our new Trek 920’s.

By the way, awesome signature line PTL! So grateful to be living an incredibly blessed life here in Western NC.

Looks like a good choice. BTW, have you visited the Southeast Regional subforum to find locals near you? Lots of NC folks on here.

Enjoy the bikes.

Thank you, will check out the SE Regional forums.

He stated "they aren't sitting on those bones". But yeah they are sitting on them. The sitbones have to be supported by the saddle or you wouldn't last 30 minutes. Anybody can put their hand under their butt while riding, in any bar position, and feel their sitbones pressing on the saddle. The contact points may change put it's physically impossible for the width of the sitbones to change. My leather Turbo saddles have permanent indentations from my sitbones. And the indentations aren't in multiple areas.

And I simply do not believe, as he stated, that customers with sit bone widths exceeding the total width of the saddle can ride those saddles with no other contact than the soft tissue in the sensitive areas. There's just no way.

I am in the same boat as the majority of people looking for a seat that isn't a pain in the @55. I get what Kontact is saying.

Yes it's true the width of the "sit bones" don't change, but they do not maintain the same distance from each other when viewed front to rear. One look at a pelvic bone image was worth a thousand words to me.

So as you lean forward onto the bars, the hips rotate forward to a section where the bones are closer together. Makes perfect sense, I just need a way to convert that into useful data for picking a saddle.

I have customers with sit bone widths exceeding the total width of the saddle.

Perhaps I am reading this wrong. I hope so. You need a saddle wide enough to support the sitbones if you want to have children someday. You CANNOT have a saddle where your sitbones exceed the total width and your weight is supported by soft tissue.

Obviously i can't speak for someone else, but this is how I understood his statement:

The way the sit bones are measures is from the customer sitting towards further back on sit bones than the actual riding position. So a measurement of say 148 at that position may change to 132 when the hips are rotated forward. If you then buy a seat that is 138, you technically bought a seat that is wider than the actual number.

Of course I could be missing something, but the concept makes sense.

If you lay a piece of aluminum foil on the carpet (which is one way to measure), sit on it straight up and then leaning forward the measured width will not change. Especially a full 16mm. You don't have to believe me, try it for yourself. It takes one minute. But in any case, specifically stating that you can have a saddle narrower than your total sitbone width is wrong. Wider than recommended is probably fine, but not narrow.

I watched this video and few others by Tony a couple of weeks ago. Excellent. It pretty much removes much the mystery for me. And debunks much of the “bull dust” I have read on various threads haha. We opted for the free Trek shop sit bone mapping out of convenience and likely better accuracy in saddle selection. So we selected our saddles based on our sit bone measurements.

You can do that. The problem is that you are talking about the contact points between two convex surfaces, rather than putting a round behind on a flat plate or floor. The choices made about the 3D shape of the saddle dictate where the contact areas are going to be to such an extent that you can't just add and subtract material to change pressure in one spot without majorly impacting pressure in some other spot.


"Sit bones" is a term that either refers specifically to the Ischial Tuberosities or more generally to the arch of bone that runs from the Tuberosities to the Pubic Symphysus. As cyclists are leaned forward, we lift the Tuberosities up off the saddle and locate the Ischial Ramus at the bottom most part of the pelvis. Since those bones are narrowing toward each other to eventually join at the pubis, they are definitely spaced much narrower than the Tuberosities are - just like an old fashioned rocking chair where the runners get closer in the back.



Anyone can make a video, and Tony10Speed doesn't know anything about bike fit anatomy. The Ischial Ramus is not covered with nerves and arteries any more the the Tuberosities are. The nerves and arteries are in the soft tissue between the bones. He should read the links he provides, because Steve Hogg does know about cycling anatomy:

Here's Steve's model of how the pelvis interacts with the saddle:




https://www.stevehoggbikefitting.com...ion-smp-seats/

As you can see, the Ischial Tuberosities are the bones floating above the P in SMP, not contacting the saddle at all at the pelvic angle at which we ride bikes.

And if you were to do the aluminum foil thing with a flat, triangular panel shaped something like a seat, you would see that the pressure marks left behind are indeed narrower than what you see when you sit on a floor because your thighs are out of the way.


Here's the kind of posture you'd need to have to get your Ischial Tuberosities in contact with the saddle:

The measurement does provide a start point, but I do agree nothing replaces sitting on them.

I used to help measure for, design, and make custom seats for racing rowing (crew) boats. We got folks to sit on a foam that deformed, then we took a scaled scan of that and got to work in CAD. Once done we used a CNC router to make a seat (basically cutting custom holes in a standard seat blank).

I don't know if I'd even go that far. If Bill has a 140mm sit bones and rolls his pelvis forward more than Carl who has 130mm sit bones, Bill might actually be sitting on narrower spaced pelvic bones than Carl.

Pelvic angle is a far more important factor.