A tree that is too narrow for the horse is the most common and most consequential saddle fit mistake. The symptoms are frequently misread as training problems or behavioral issues.
A narrow tree arch presses into the sides of the horse's withers rather than clearing them, creating pain at the contact points and restricting the forward swing of the shoulder blade with every stride. Almost always misdiagnosed as a training problem.
Place the saddle on the horse's bare back without a pad. Look at the gullet arch over the withers. You should fit three to four fingers between the arch and the top of the withers. If the arch is pressing on the withers, the tree is too narrow. From the front, check that the tree points sit against the wither side without digging inward.
Gullet arch contacts or presses into the top of the withers. Tree points dig inward at the wither sides. Less than two fingers clearance in the gullet.
Front of bars sits on or over the shoulder blade. With forward movement, the rotating shoulder blade contacts the bar with every stride.
Short choppy front stride. Reluctance to extend. Hollowing through transitions. Reining horses show restricted stops and reluctant spins.
Head elevation when saddle is placed. Pinning ears during saddling. Cold-back behavior that presents as bucking or strong reluctance to move forward.
Adding padding raises the entire saddle higher but does not widen the arch. The arch remains exactly the same width, now pressing into the withers from a higher position. More padding on a narrow saddle frequently makes the problem worse. If the tree is too narrow, the saddle must be replaced with one built on a wider tree. This is non-negotiable.
If buying remotely from David Solum's inventory, provide a wither tracing before purchase. Bend flexible wire to your horse's wither shape 2.5 finger-widths behind the shoulder blade. Trace onto paper. David can compare this to any saddle in his inventory to assess fit before the saddle ships.
David Solum has been evaluating saddle fit problems for 40+ years. Call, text, or email him directly — he can advise on whether it's a fit issue, a tree problem, or a saddle you should replace.
See also: Free Saddle Tools · How to Fit a Western Saddle · Parts of a Western Saddle · How to Buy a Certified Used Saddle