Proper channel width of your saddle may be the most important fit parameter and if the channel is too narrow, putting on a thicker pad will only make it worse. The saddle should completely clear all processes of the horse’s vertebra and sit on the longissimus muscle. If the channel is too narrow the horse will suffer pain and damage to his spine can happen very quickly. If the channel is too wide, the longissimus muscle will not be weight-bearing and the saddle will probably lack lateral stability.
A Port Lewis Pad saddle analysis will tell you exactly where your horse is bearing the weight of the saddle. After riding, when you remove the saddle and leave the Port Lewis pad on the back, you can see if there is any contact too close to the horses’ spine. The best information comes from examining the pad while the it is still on the horses back, but pictures of the pads with light showing through them, are also very informative. There should always be a strip of dark red down the center of the pad. Some horses need a thin strip and some horses need a thick strip. These pictures are from two different saddles on the same horse. The impression in Figure 2 shows a dangerous situation. There is no channel clearance. The saddle that made Figure 3 had the proper channel width for this horse, but the wool flocking was very hard. You can see that the panels are not making a wide soft contact and there is a clear pressure point on the top left.