The other day, I went to a bike shop and measured my sit bones width on the Prologo's "assometer" ( ). According to it, the measurement falls between 115mm and 120mm, so they told me the maximum saddle width for me is 143mm.

After that, I found out that my relaxed torso angle on my late 90s "MTB" bike is of around 50 degrees, which is closer to 45°("sports"/"performance" position) than to 60° ("moderate"). In addition, I regularly find myself leaning into a more aggressive position on descents, perhaps of 30°, and also changing position on the saddle when climbing. So maybe I could consider myself a dynamic cyclist.

Moreover, according to https://www.selleitalia.com/size-guide/ , I have a normal/neutral pelvis, and my relaxed hip flexibility is medium. (If I force myself to touch my toes, which I can do, the "upper spine" flexes a lot.

But there are problems: my left hamstring is a little bit tight by nature. (The right one isn't tight at all; my right leg is the dominant one.) So, occasionally I get a little bit of low back discomfort on the left side, even though my saddle height is correct. (I think my 175mm cranks are too big for me, they close too much the hip angle). In addition, I currently have a 145x270mm wavy saddle with a slight relief channel that doesn't seem to suit me; it doesn't allow me to roll my pelvis forward without pressuring my genitals and flexing the upper spine ("hunching"). I also rub the right thigh on it (dominant right leg, remember?), maybe also because of the wide/slow transition curve.




So... what saddle width should I choose? 130mm, 135mm, 140mm...? Should I get a slightly wavy saddle or a flat one? What length to you recommend?

Another picture of the saddle (also not taken by me):

so, this is the internet, so we don;t have direct knowledge of everything mentioned about yourself...
the ischium bones /sitzbones are angled and so become 'narrower' as you tilt the pelvic area forward - so, no reason to go wider ...
...even though the saddles I currently use have a small fore/aft 'saddle' effect, I am not set completely level - I have mine set to be a bit nose down, a couple degrees (done by 'feel')
which mostly eliminates 'pressure'. And I have NO tendency to slide forward with this slight nose downward - just reduces pressure.
If you have left leg hamstring issues, I would set the saddle height with consideration for that - if not too drastic change, the right leg should 'adjust' to the change in a week or 2 of rides...
I have always done OK with most saddle shapes, but now tend to go more toward 'flatter' side to side profiles than before - just more comfortable for my old hips/bones.
The saddle you show - BTWIN (Decathlon) is prolly an OK saddle, but there are better...
Try a saddle with a very defined central channel/cutout - some cutouts are very generous these days and offer more relief.
There are saddles where the nose is actually fully 'split' with nothing directly under the gentials...
There are also the new short nose/'power' designs, which many riders now like. I tried a few and though nice, didn;t offer me any more than the saddles I now use...
But different for every rider.
Go to a shop which will let you try a saddle for a few days and take return to try another...
If they have a good selection, you may find one which works best for you.
Let your Butt make the decision, not your eyes...
Ride On
Yuri
EDIT: many riders set their saddle height while being/sitting quite upright . When one tilts forward into their riding position, the pelvis tilts forward and slightly raises the hip sockets - which 'shortens' the reach of the legs. Best to set saddle height when tilted 'forward' into your riding position.
Also, saddle fore/aft affects the 'reach' to pedals. moving saddle aft makes the reach feel longer, opposite for moving forward (when you go forward, raising saddle slightly is common...)

Saddle width recommendations are for Specialized brand saddles only. They are absolutely not universal.

The saddle Kontact makes would address your needs.

also, you mentioned the 175 cranks - but haven't said what your cycling inseam measurement is (nor your height. less important and which might not be the determinant factor).
The longer cranks do require more hip flexibility, and the tight hamstring will resist that...
if you can, try riding a 170 crank, or shorter; specifically to how your muscles and connective tissue likes less needed motion range. Which also allows easier spin.
A 172.5 as compared to 175, is not enough difference to make a difference. Even a 170 isn't much change, but might feel a bit better.
I tried and could easily ride 175 - found that I was able to push a gear just a bit more.
But in the long run, a more comfortable pedal stroke/spin helps my legs stay 'fresher' throughout a longer ride.
Ride On
Yuri
EDIT: reread, and last comment on using 175... I went back to using 172 & 170, just better for spinning om longer rides...

Thanks for replying. I wish I could find an entry level Shimano crank of less than 170mm.

My inseam measurement is around 780mm and saddle height is 645mm from bottom bracket to saddle, or 795mm from pedal to saddle. (The sole of the shoes is 15mm height, flat pedals 5mm. Bib shorts padding is 5mm when compressed. Thus, 780+20-5=795.)

I recently rode around 30km up and down and didn't feel any discomfort on my lower back during and after the ride, right after I made small changes to the saddle position: moved it forward 2.5mm and tilted the nose down 0.5 degrees. I immediately felt I was sitting on a different part of the saddle and perhaps sliding a little bit forward, but without the thigh rubbing/touching the saddle. I'll try to level the saddle next time.

Now, do you think a 135mm curved saddle would work for me, or would it be too narrow?

Why would a non Specialized saddle of any width be too narrow?

There is no legitimate connection between your sit bones and the outer width of a saddle.

Looks as you've done a lot of homework. All good to know.
Wondering, with the inseam you're saying, why you would consider riding with 175 cranks (as you noted) ?
the measure of fore/aft, height and how you might find a tilt angle are not some hard numbers, they are just references for you, to compare when you might make a change...
Each/any saddle might have a different 'feel'/effect on how they work for you, so setting to a measurement is likely only a 'start' point from which you might modify with 'on-saddle' time.
as you noted...
What I think is that I can't say anything about how appropriate a saddle might be for you... The saddle width is only one factor, The curvature and transition are just as important.
For me, I do best with saddles which have a flatter curvature and a quicker, more pronounced transition.
If you don't like how a saddle might be rubbing you, then look for a saddle with a quicker/sharper transition.
And depending on your body morphology, a flatter curvature might support more and keep the 'private' parts from pressure problems.
Ride On
Yuri

Too much homework IMO. Original post is a classic example of 'too much knowledge' being dangerous. Ironically, for as much information as that post was loaded with, some information about the bike, and the o.p. themself (height, weight, overall build) might have been useful? Maybe. Maybe not. I think your first post to the o.p. was about as good as it gets. I have to think saddle height has to trump crank length in significance. I cannot find it in me to think the higher knee from a longer crank means much in the grand scheme.

For a 50° back angle, for me personally, a 135mm saddle would be way too narrow. They are probably sitting more upright than that anyway. Closer to 60° very likely. For that kind of position (for me) a cut-out is not a must. The BTWIN saddle could work for me. The Bontrager Affinity I use on that kind of bike is very flat with a minimal center groove, much like the BTWIN. Mine is 145mm. I am 5'10" and 205lb. So, not small, but beefy, if that makes sense.

But the outer width correlates to the sitting area (depending on the saddle's curvature, of course), which correlates to the sit bones distance. I also have a flat saddle measuring 148mm but the sitting area is only 120mm. It has a cutout and a fast transition curve but it doesn't work for me. Also, it's harder than my current saddle.

Like I said, my position on the bike is closer to 45°. I have filmed myself to check it out. If I raised the handlebar, I would be closer to 60°.

Not an answer for most of your questions but that right thigh rub - try twist the seatpost a touch to the left. Many of us men do that. I run the nose about 7mm the left of dead center. This affects very little else.

I've never liked using back angles for this reason. The difference between a true 45 degree and 60 degree angle is HUGE. You could not possibly achieve both by "raising the handlebar". And what kind of handlebars are we talking about? Drop bars? 45 degrees with flat-bars would be a bear. IMO you need to forget everything you know about 'fit'. Everything. Forget it. Allow yourself to be informed. You got some good information in this very thread. "Doesn't work for me". Hmm. Respectfully, you don't know what you don't know.

No, it doesn't. The outer width is based largely on the way the saddle curves away from the top portion you sit on. Some saddles have large tops that quickly drop off the sides. Specialized saddles do not.

I appreciate the way you are trying to approach this with an eye toward metrics, but saddles don't really work that way. They aren't designed with pelvic tilt angles in mind. You don't sit on your 'sit bones' (ischial tuberosities) but the narrower ischium. And which part of the ischium you sit on is not something you can find out without a pressure map, because pelvises are actually much more varied than you might imagine. I know for a fact that people with sit bones exceeding the total width of the saddle they are riding because they aren't sitting on them. Saddles aren't kitchen chairs.

On top of all of that, the soft tissues between the pelvis and saddle also vary greatly in thickness, density and sensitivity. For instance, some riders greatly prefer angled sides, others need a flat surface. There is no rhyme or reason to that, because bodies and preferences vary too much to treat saddle selection scientifically. All you can really do is look for a saddle that meets many of your basic needs and then try it out.

Thanks for confirming what I already knew except the part about soft tissues. I don't care about the brand of the saddle. If my sit bones are indeed between 115mm and 120mm, and my hip angle on the bike is around 50 degrees, then a 135mm curved saddle would likely work, even a 130 might work. This is what I want to know. I'll just have to try a narrower saddle and see if it works.

Okay. So I'm going to suggest you try one of ours.