I hear this sort of thing way more frequently than I'd like. Tree width is the very first thing most people think about when they talk about saddle fitting, yet many people don't understand that it's only one part of the fitting picture. Yes, the correct tree width is important, but tree type, tree shape, panel configuration and billet configuration are equally important, and all but the last have an effect on width. But people always start with, "My horse needs a medium/wide/narrow/extra-wide tree ..."
So let's break this down. First, whether a tree is given a designation like medium or wide, or whether it's given a centimeter measurement, the measurement is taken pre-construction, on the bare tree. If the tree is measured in centimeters, the measurement is taken between the ends of the tree point. If it's a UK-made saddle, it's given its width designation based on the angle of the pommel arch, as follows:
- Narrow: 75°-84.9°
- Medium: 85° - 94.9°
- Wide: 95° - 104.9°
- Extra-wide: 105° and up
Reason one: Tree type. If a saddle is a wide standard tree, it's not going to fit the same as a wide hoop tree, since the hoop tree has the extra breadth across the top of the pommel arch.
Reason two: Head height. A medium width high-head saddle may work beautifully for a higher-withered horse, but will probably perch on a horse with a lower wither.
Reason three: Tree point length. Long tree points fit less generously than short tree points. In the graphic below, the ends of the "tree points" are the same width apart, but note how much more room there is with a shorter point.
Reason four: Panel configuration. A wither or full front gusset will reduce a saddle's width. A K or trapezius-type panel, which can be a lifesaver on a horse with divots behind the withers or real "steeple" withers, can make a saddle perch on a propane-tank back. Where the panels are sewn into the pommel arch makes a difference, too; that's why Passier's Freedom panels (which are sewn in lower in the pommel arch than their standard panels) are a good choice for a horse with a lower, muttony wither. (I rode the Great Red Menace in a Passier GG for years; she wasn't quite a hoop tree candidate but was broader than a regular tree would easily accommodate, and this "compromise"- especially in conjunction with the shorter tree points on the Passier - worked well until she got older and widened into a real hoop tree horse.) Horses with bigger withers often need the panels to be tied in higher in the pommel arch (but not so high that they press on the lateral aspect of the spine).
Reason five: What's in the panels. Foam panels are thinner than wool panels because they have better cushion; an inch of foam offers much more cushion than an inch of wool. Foam panels offer a closer "feel" but don't usually offer much in the way of panel modifications (though some saddle companies, like Beval, are starting to pay more attention in this area). I don't think they're usually a good choice for a horse with a big wither, since the panels are often too minimal to support the saddle in proper balance on a horse with that conformation. These panels can work well on the table-backs, though; Andy Foster's Lauriche saddles are all foam-paneled, and I've seen many of them work beautifully for the propane-tank builds.
Wool panels, on the other hand, are bulkier, and the amount of flocking in the panels can make a pretty substantial difference in the way a saddle fits. A saddle that's been heavily flocked in the front will not fit as generously in width as a saddle that's been more lightly flocked ...but as we learned in the previous blog post, you can't go to the other extreme, either. There must be enough wool in the panels to cushion the horse's back from the tree, but not so much that the panels are distorted into leather-covered sausages.
So the next time you're saddle shopping, remember that correct tree width is vital, but that these variables will make it almost impossible to say with any assurance, "My horse needs a ______ tree."