The worst thing you can do to your horse is adjust his side-reins too tightly. This can have a number of effects on him. First, he may lean on the bit and fall on his forehand. Second, it may cause stiffness in his neck which could extend to his back. Third, he will either run away from the restraint or will be unable to move freely forward.

So how do you know that the side-reins are fitting properly? The answer is simple: after warming up your horse on the lunge without side-reins, ask him to halt and allow him to catch his breath. Attach the side-reins to the bit and allow enough length to form a straight line from its base at the girth straps to the horse’s mouth. The horse should be carrying himself in a natural outline, his head and neck positioned just as he wanted them to be when he halted. This is what I call the free outline.

Ask the horse to trot a circle or two then halt him again. Walk up to him and take about two inches out of the side-reins. Trot on two circles and watch carefully. Is there excess slack in the side-reins? If there is, halt the horse and take out another inch or two. By now, the horse’s nose should be slightly in front of the vertical. This is as tight as your side-reins should be. Eventually, you will know from the first attempt how much to tighten the side-reins.

Remember that the side-reins should be of equal length. The other end of the reins will be attached to the second girth strap as low as the bottom of the saddle flap. See photo on the right, courtesy of Horse & Rider magazine.