Place the saddle (without a saddle pad and without irons) over the withers and slide it back behind the shoulder blade. On a dressage saddle, the cantle should be a little higher than the pommel, on a jump saddle it should be even.
Use a pencil and place it on the seat. On a balanced saddle the pencil should stay in the center of the seat. If it rolls too far forward, the pommel is too low and if it rolls backwards, the pommel is too high.
You should be able to place 2 to 3 fingers between the top of the wither and the saddle and you should also have the same clearance on each side of the wither, to allow the shoulder blade to move freely. White hairs, bumps or sores are signs that the saddle does not allow sufficient wither clearance.
Gullet Channel Width
The gullet channel should be wide enough that the saddle rests on the back muscles of the horse on each side of his spine. There isn’t a “one size fits all” gullet channel width, but it is very important that the width is the same throughout the length of the saddle. When you place yourself behind your horse, you should be able to see his wither clearly through the gullet channel.
Full Panel Contact
The next step is making sure your saddle panels are fully in contact of your horse, to ensure the rider’s weight is distributed equally on the entire available surface. Two of the most common problems are a saddle that bridges or rocks.
In a saddle that bridges, the front and rear of the panels are in contact with the horse, but the middle is not. This results in excessive pressure at the front and rear. To check if your saddle bridges, slide your hand between the panel and your horse and feel if there is any area where there is no contact.
A saddle that rocks has a motion similar to a rocking horse. There is excessive pressure in the middle and the rider’s weight will also shit to the front and rear when the horse is moving. To check if your saddle rocks, place your saddle on your horse without a saddle pad and push down on the pommel. If the cantle lifts up, your saddle rocks.
If your saddle billets are not positioned correctly, your saddle will not stay in place when you ride, no matter what type of saddle pad or girth you use, it will most likely slide forward.
Once the saddle is placed correctly behind the shoulder, the billets should hang perpendicular to the ground and should be in the girth area (at the narrowest point of the rib cage behind the horse elbow). If the billets are too far in front or behind, the girth will always pull them towards the girth area and this will result in an unbalanced saddle.