I will place this bare tree on my horse marking the spots where it touches and the spots where it doesn't. I will then add filler to the spots that don't touch and grind the high spots down. Over the next few days I will try and fit the tree to his back giving me maximum contact.
PSI is the my weight divided by the square inches that contact his body. This should not exceed 1 psi or the back can become sore. I have dad saddles with almost 300 square inches but I am afraid I can not get more then 120 square inches of support out of this saddle putting the pressure on his back at about 1 1/2 psi/pounds per square inch.
I would like to finish the tree off with a nice covering of foam about 1/2 inch thick over the entire underside before putting the factory cover back on.
At the same time I move the billets for the girth back about 3 inches making the saddle cinch down more in the center then forward.
All this is an effort to keep his back in good shape and keep him running happy.