18" Stubben Tristan--sizing?

I'm not good at saddle sizes..so I was wondering, would an 18" seat fit? It's a dressage saddle. I'm 5'7/140lbs. Any more tips on saddle seat sizes ect would be appreciated. Thanks!

It might be a bit large. I am 5' 4" and MUCH heavier than you and ride in an 18.
But it wouldn't be outragesouly large and might be just fine, especially if your height is more in your leg than your torso.

A lot depends on your build and personal preference. I ride in both a 16.5 and a 17 and I am 5'3" and ~150lbs so it's hard to say that one thing will specifically work or not work for someone. ;)

What crimsonsky said.

I rode in a 17" (GP) saddle - on the same horse - for 23 years. I'm 5'11" and weight changed from 9 - 12 stone as I aged:(
Tree-shape changes meant I needed a 17 1/2" for the next horse.

My wife and daughter (5'7" and 11 stone and 5'9" and 12 1/2 stone) both used 18", daughter mainly because she has a very long femur compared to her upper-body length.

Don't forget the horse also has to be able to take the longer panel length :)

Thanks y'all (:

I am going to guess that an 18" is too big for you, in fact I would bet money on it. An inch will impede your ability to get your best riding ability out to the forefront.

I rode in a 17.5" Stubben Siegfried yesterday and it fit me perfectly. I'm 5'9" and 140 pounds. I'm not familiar with the seat on the Tristan as compared with the Siegfried, but I would guess that it would be just a td too roomy for you. I would think the flap and stirrup bar might be in the wrong place for your femur-length more-so than the seat being too big. I'm the same weight as you, and a slightly bigger seat size would have been a little large for me, but not horribly large. However, at 5'9" and very leggy, the flap on that 17.5" saddle was just right for me. You having shorter legs than me (I assume) would probably be a little off balance or chair-seat a little in an even bigger saddle.