Curb bit
A curb bit is a type of bit used for riding horses that uses lever action. It includes the pelham bit and the Weymouth curb along with the traditional "curb bit" used mainly by Western riders. Kimberewicks are modified curb bits, and a curb bit is used in a double bridle along with a bradoon. A curb bit is, in general, more severe than a basic snaffle bit, although there are several factors that are involved in determining a bit's severity. Liverpool bits are a type of curb bit commonly used for horses in harness. The curb bit The curb bit consists of a mouthpiece, curb chain, and a shank, with one ring on each side of the purchase arm of the shank, and one ring on the bottom of the lever arm of the shank. Pelham bits add a ring for a snaffle rein, next to the mouthpiece. Action A curb bit works on several parts of a horse's head and mouth. The bit mouthpiece acts on the bars, tongue and roof of the mouth. The shanks add leverage and place pressure on the poll via the crownpiece of the bridle, to the chin groove via the curb chain, and, especially with a "loose jaw" shank, may act on the sides of the mouth and jaw. The shank A curb bit is a leverage bit, meaning that it multiplies the pressure applied by the rider. Unlike a snaffle bit, which applies direct rein pressure from the rider's hand to the horse's mouth, the curb can amplify rein pressure several times over, depending on the length of the curb's bit shank. Shank sizes vary from the Tom Thumb (2 inches long) to more than 5 inches. The longer the bit shank, the more powerful its potential effect on the horse. For this reason, overall shank or cheek length, from the top of the cheek ring to the bottom of the rein ring, usually cannot exceed inches for most horse show disciplines. Leverage principles The relation of the upper shank (purchase)—the shank length from the mouthpiece to the cheekpiece rings—and the lower shank or lever arm—the shank length from the mouthpiece to the lowest rein ring, is important in the severity of the bit. The standard curb bit has a " purchase and a " lower shank, thus producing a 1:3 ratio of purchase to lower shank, a 1:4 ratio of purchase to full shank, thus producing 3 lbs of pressure on the chin groove and 4 lbs of pressure on the horse's mouth for every 1 lb placed on the reins (3 and 4 newtons respectively for every newton). Regardless of the ratio, the longer the shank, the less force is needed on the reins to provide a given amount of pressure on the mouth. So, if one were to apply 1 lb of pressure on the horse's mouth, a 2" shank would need more rein pressure than an 8" shank to provide the same effect. A long lower shank