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DIY Sit Bone Measurement

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DIY Sit Bone Measurement

Old 01-20-22, 02:45 PM
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napalmradio
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DIY Sit Bone Measurement

Anyone have a good method on measuring your sit bones at home? Looking to get a new saddle and just not sure what size I should get. Generally I'd guess I want the most narrow, but I'm just unsure.

Thanks!
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Old 01-20-22, 03:26 PM
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If you have hard bench, and a piece of corrugated cardboard, sit on it while hunching forward as you would on the bike. Don't wear padded shorts. Measure between the centers of the depressions.
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Old 01-20-22, 03:56 PM
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Helps to pull up on the bench or chair surface so that you actually dent the cardboard with your bones.
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Old 01-20-22, 04:18 PM
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Originally Posted by Mojo31 View Post
Helps to pull up on the bench or chair surface so that you actually dent the cardboard with your bones.
Or weigh a lot. That's how I did it.

Also helps to pull your knees up to your chest which makes the sit bones more prominent.
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Old 01-20-22, 04:35 PM
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I fell for the ass-o-meter, measure your sitz bones theory for finding a comfortable saddle at one time. That was a big fail for me. The most comfortable saddles for me had no correlation at all to the distance between my pelvic bone prominences. In fact, it wasn't even close.

In my opinion, you can't find a comfortable saddle with a ruler. Unfortunate, it is all trial and error. Ebay ended up being my best friend allowing me to try and resell 6-7 different saddles before I found the one that I have now used for 15-20 years.
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Old 01-20-22, 05:05 PM
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There's the sheet of tinfoil on a stair step method. Kind of a variation of the cardboard method, but I find it makes a more defined ass-print! I don't find this measurement massively useful, but gives some idea of where you "sit" in the overall range. Like if you find that you have much wider than average sit-bones, then a narrow saddle is probably not going to work. But if you have narrow sit-bones, you might still find that you prefer a wider saddle.
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Old 01-20-22, 05:24 PM
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Originally Posted by genejockey View Post
Or weigh a lot. That's how I did it.

Also helps to pull your knees up to your chest which makes the sit bones more prominent.
depends on your padding.
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Old 01-20-22, 05:32 PM
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Originally Posted by jrobe View Post
I fell for the ass-o-meter, measure your sitz bones theory for finding a comfortable saddle at one time. That was a big fail for me. The most comfortable saddles for me had no correlation at all to the distance between my pelvic bone prominences. In fact, it wasn't even close.

In my opinion, you can't find a comfortable saddle with a ruler. Unfortunate, it is all trial and error. Ebay ended up being my best friend allowing me to try and resell 6-7 different saddles before I found the one that I have now used for 15-20 years.
Rather than "no correlation," I would say that sit bone distance is only a single factor and not even generally the most important factor, and that saddle shape (i.e., bird's eye view) and topology (i.e., from the rear) are far more important factors, especially since most saddles are available in at most two sizes which differ by 10 mm to 13 mm in width.

To measure my seat bone distance, I touch each one with the corresponding index finger and asked my wife to measure the distance between my index fingers.
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Old 01-20-22, 05:36 PM
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Originally Posted by SoSmellyAir View Post

To measure my seat bone distance, I touch each one with the corresponding index finger and asked my wife to measure the distance between my index fingers.
Ah, so they can be useful after all!
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Old 01-20-22, 05:37 PM
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Originally Posted by PeteHski View Post
Ah, so they can be useful after all!
Of course index fingers are useful. How else would you brake (from the drops) or exercise your 2A rights?
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Old 01-21-22, 07:15 AM
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Yeah I know all butts are different and the sit bones aren't a silver bullet. Just figured it was a decent place to start. Thanks for the tip about ebay though! That's a great idea.
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Old 01-21-22, 07:57 AM
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There's one important thing to realize in fitting a saddle based on "sit bone" width. In this drawing the "sit bones" are labeled "ischial tuberosity." The problem for road cyclists is that one only sits on the sit bones when in an upright riding position and any semi-aggressive posture rotates the rider's weight forward onto the pubic rami, which rapidly narrow. On my bikes, it's basically impossible to weight the sit bones for more than a few seconds while resting.


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Old 01-21-22, 08:14 AM
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A lot of saddles have gone through my shop over the years for me, family and friends. I am with jrobe on this, while my sit bones have not moved my saddles have shifted over the years. Now in my 70s with bars rising my saddles have shifted again and I prefer suspended leather saddles for the first time.
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Old 01-21-22, 08:58 AM
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Originally Posted by moalpha View Post
there's one important thing to realize in fitting a saddle based on "sit bone" width. In this drawing the "sit bones" are labeled "ischial tuberosity." the problem for road cyclists is that one only sits on the sit bones when in an upright riding position and any semi-aggressive posture rotates the rider's weight forward onto the pubic rami, which rapidly narrow. On my bikes, it's basically impossible to weight the sit bones for more than a few seconds while resting.


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Old 01-21-22, 09:35 AM
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Originally Posted by PeteHski View Post
There's the sheet of tinfoil on a stair step method. Kind of a variation of the cardboard method, but I find it makes a more defined ass-print! I don't find this measurement massively useful, but gives some idea of where you "sit" in the overall range. Like if you find that you have much wider than average sit-bones, then a narrow saddle is probably not going to work. But if you have narrow sit-bones, you might still find that you prefer a wider saddle.
I did this method too. Put foil on a piece of cardboard then sat on my steps.

I agree its just a basic guide and can be very helpful. I purchased my first saddle off this method but wasn't 100% there. Then got a bike fitting and that was a great process and that was the "ah ha" moment for my cycling comfort.
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Old 01-21-22, 09:41 AM
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Originally Posted by MoAlpha View Post
There's one important thing to realize in fitting a saddle based on "sit bone" width. In this drawing the "sit bones" are labeled "ischial tuberosity." The problem for road cyclists is that one only sits on the sit bones when in an upright riding position and any semi-aggressive posture rotates the rider's weight forward onto the pubic rami, which rapidly narrow. On my bikes, it's basically impossible to weight the sit bones for more than a few seconds while resting.


Very good point, but would that not be taken into account by saddle manufacturers in respect of their various width options - sit bone width being merely a convenient reference point? If somebody has narrow sit bones, then it follows that their pubic rami would also be narrow relative to someone with wider sit bones.

But I do think that riding posture has more influence on saddle choice than sit bone width and some saddle manufacturers do seem to design their saddles around riding posture, with width as a secondary option e.g. Fizik
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Old 01-21-22, 09:50 AM
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Originally Posted by PeteHski View Post
Very good point, but would that not be taken into account by saddle manufacturers in respect of their various width options - sit bone width being merely a convenient reference point? If somebody has narrow sit bones, then it follows that their pubic rami would also be narrow relative to someone with wider sit bones.

But I do think that riding posture has more influence on saddle choice than sit bone width and some saddle manufacturers do seem to design their saddles around riding posture, with width as a secondary option e.g. Fizik
Agree. My point was that it's the taper, not the back of the saddle, where the width parameter affects fit for roadies.
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Old 01-21-22, 07:04 PM
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Originally Posted by MoAlpha View Post
Agree. My point was that it's the taper, not the back of the saddle, where the width parameter affects fit for roadies.
Totally agree. Definitely a good point to keep in mind when choosing a saddle
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Old 01-23-22, 04:56 PM
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DANG, guess there's no more office photo copy machine any longer.
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Old 01-24-22, 06:05 AM
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Originally Posted by OldTryGuy View Post
DANG, guess there's no more office photo copy machine any longer.
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Old 01-24-22, 06:08 AM
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Originally Posted by MoAlpha View Post
Agree. My point was that it's the taper, not the back of the saddle, where the width parameter affects fit for roadies.
Thanks so much for the info! I've been using a cheap WTB saddle on my gravel bike and I'm good doing about 50 miles on that. But I've been battling saddle sores with it and I've got a road bike on the way so I want to make sure I can do longer rides more consistently. I'm not racing anyone, so I'm usually in a more upright position but it's still good to know about the taper you mentioned.
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Old 01-24-22, 09:38 AM
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Originally Posted by OldTryGuy View Post
DANG, guess there's no more office photo copy machine any longer.

you break the glass on one machine and your labeled for life.
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Old 01-24-22, 10:07 AM
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Probably more important than width, unless you're far outside the norm, is shape. I'm pretty inflexible, can't reach beyond mid calf when trying to touch my toes (it's not age, I've never been able to), so I'm most comfortable on "wave" saddles that allow me to rotate my pelvis forward.
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Old 01-24-22, 06:36 PM
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Originally Posted by OldTryGuy View Post
DANG, guess there's no more office photo copy machine any longer.
Even if your office is not paperless, why would the photo copy machine have X ray vision?
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Old 01-24-22, 06:52 PM
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Originally Posted by PeteHski View Post
Very good point, but would that not be taken into account by saddle manufacturers in respect of their various width options - sit bone width being merely a convenient reference point? If somebody has narrow sit bones, then it follows that their pubic rami would also be narrow relative to someone with wider sit bones.

But I do think that riding posture has more influence on saddle choice than sit bone width and some saddle manufacturers do seem to design their saddles around riding posture, with width as a secondary option e.g. Fizik
With Specialized saddles, they have a simple chart where you start with the sit bone width and then factor in the hip angle, so someone with a less aggressive position may be on a different saddle than someone else with the same sit bone width and a more aggressive position.
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