Fitting and padding a pack saddle correctly is as important for a pack animal's comfort, soundness, and longevity as saddle fit is for a ridden horse. The pack saddle must sit level on the animal's back, clear the spine throughout its length, distribute pressure evenly across the bars of the tree, and remain stable under load without rocking or shifting.
The pack saddle tree must match the animal's back width and angle. A tree that is too narrow will create concentrated pressure on the outside of the back muscles, while a tree that is too wide will drop down and create pressure directly on the spine — both situations produce soreness with repeated use. Many experienced packers develop an eye for tree fit over years of working with many animals.
Padding beneath the pack saddle must be thick enough to provide cushioning, conformable enough to follow the animal's back contours, and positioned correctly to protect the spine and withers. The most common mistake is using a pad that is too small, which leaves the edges of the pack saddle in contact with the animal's back without adequate cushioning. A damaged or compressed pad that no longer provides adequate thickness must be replaced immediately.