How do I fit a harness correctly and what are the most common fitting errors?

Correct harness fit is one of the most important competencies in driving horsemanship, and it is an area where many drivers have gaps that create discomfort, inefficiency, and safety risks in their horses without recognizing the connection between the fitting error and the horse's behavior. A horse that resists moving forward willingly, tosses its head during driving, shows tension through its back, or develops sores at specific harness contact points is often communicating a fitting problem. The breast collar should lie across the chest at approximately the level of the point of shoulder, high enough to be above the windpipe but low enough not to restrict shoulder movement. A breast collar positioned too high interferes with breathing; one positioned too low slides off the chest during the pulling work and allows the traces to drop below their effective angle. The saddle or backpad must be positioned and fitted similarly to a riding saddle, avoiding pressure on the spine and distributing weight across the panels evenly. The girth that secures it should be snug but not restrictive. The crupper, which passes under the horse's tail to prevent the saddle from sliding forward during uphill work, must be correctly positioned — not so tight that it creates pressure on the dock, and not so loose that it fails to prevent forward sliding. Many horses require a gradual introduction to the crupper because the sensation of pressure under the tail is unfamiliar and potentially alarming.