The back cinch of a saddle is the strap that secures the back of a saddle and keeps it from rising off the horse’s back. It is commonly used on roping horses whose saddles get a lot of forward pressure when backing and holding a steer at the end of a rope.
It is fastened to the rear of the saddle and runs around the widest part of the horse’s barrel (just under the cantle of the saddle). It is held on by a simple heavy leather billet (strap) on each side of the saddle that is attached to a Dee ring bolted into the saddle tree.
The back cinch should be tight enough to be snug up against the horse’s belly but not tight enough to cause discomfort or bucking. To keep it from moving too far back on the horse, it is usually attached to the front cinch (under the horse’s belly) by a small piece of leather. (see Saddle Cinches)
A saddle that has both a front cinch and a back cinch is called “double rigged”.
Common practice says that many equine working and sporting activities are enhanced by use of a back cinch. It keeps the saddle closer to the horse during quick starts, stops and turns such as Barrel Racers encounter. The more stable the saddle, the more stable the rider.
There is credible conversation about the back cinch being effectively useless in securing the back of a saddle in any really meaningful way if it is not firmly cinched. By the time the cinch is hanging 3″ below the horse’s belly and then can rise about 6″ into the soft underside of the horse, the back of the saddle may rise as much as 9″. Most pleasure riders could not keep their seat with their saddle abruptly 9″ high in the rear.
Any bucking becomes almost impossible to ride when the back of your saddle comes off the horse and hits you in the kidneys. Even a short kick-up is more exaggerated if the saddle-back is loose. It is disastrous of a horse gets his hind leg caught in it. And spurs can also become caught if a rider is not cautious about staying out of that area.
It is a common misconception that a flank cinch will prevent a saddle from moving forward on a horse during downhill riding. A crupper is a piece that connects to the back of the saddle and goes around the base of the horse’s tail.
Yes, you are right. It is my experience that the back cinch is most effective in stopping the saddle from tipping forward (bringing the back of the saddle up off of the horse) during activities like roping where the rope wraps around the horn and the direction of pull is forward and down from horn to calf. Any activity that requires the rear of the saddle to stay close to the horse’s back is helped by this cinch if properly mounted. However, keeping the saddle from sliding forward is not one of its uses.