this saddle is not good for horse. all of traditional saddles and good saddle without tree have in the middle, a space where the top of bones are protect of wheigt.
A lot of real treeless saddles are made without spine clearance, like for example those of Heather Moffet (although her latest does have it?), the Ansur etc... They claim that if the saddle really follows the shape of the withers and back (so isn't straight cut but curving), you don't need spine clearance as you have already distributed your weight left and right from the spine through your seatbones.
About the girth: that won't push down on the vertebrae if you don't tighten it really hard - which is impossible because then the pad is deformed. The problem you mention however does arise when you attach stirrups to it, because then you do place a large part of your bodyweight on a small leather belt that runs over one or two vertebrae, really crushing those! Also then you get the problem that the entire pad is put under more downwards pressure, pulling the center down hard on all the other vertebrae too.
So in that case your story rings really connects with me, but when riding without stirrups there just isn't that intense downwards pull because you just sit on your seatbones and your legs hang down from the sides too without pushing down, which happens when you use stirrups.
By the way, now I do notice the large buckle too- isn't that a bit annoying under your leg? Do you feel it, or is it Sjors' belly that's pushing your leg forwards?
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