Join Date: Dec 2010
Location: southern Arizona
There is more than seat size alone involved. The angle of the cantle in the rear, the height, position and shape of the poleys, the twist of the saddle, how short you like your stirrups, etc - all affect if it feels right. I was told there should be about enough room between your thigh and the poley to slip your finger in the gap. I have more than that in my 18" saddle, but it feels fine to me - possibly because of the overall shape of the saddle. I've spent plenty of hours in the 17" one, and my thighs just about touch the poleys. The 15" western saddles I've tried all are just a bit tight for me, although I could get away with riding in them. YMMV.
"Make the right thing easy and the wrong thing...well, ignore it mostly."