Curb bits are a standard piece of gear for any Western rider, but the bits have a place in the English and driving world, too. Curb bits are a useful tool for a horse that is a strong puller, such as one that becomes excited while on the trail or over jumps. Curb bits allow the rider to give much more subtle rein aids than with many snaffles, as well as encourage a horse to flex and carry their heads on the vertical, like dressage horses, which are ridden in a double bridle with both a curb and snaffle bit in their mouths.
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Where Pressure Is Applied
A curb bit works on three points of the horse’s head when the reins are pulled: the mouth, the chin, and the poll. Like a snaffle, there is some pressure placed on the bars of the mouth when the reins are pulled. Depending on the style of the mouthpiece, there may also be action on the tongue and the roof of the mouth.
Unlike the action of a snaffle, that only places pressure within the mouth, the shanks of a curb bit act as a lever. This pulls down the crown of the bridle, puts pressure over the poll, or the top of the horse’s head, and pulls the curb chain or strap forward against the horse's chin.
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The Role of the Curb Strap
The curb strap not only creates pressure but also prevents the bit from rotating too far around in the horse's mouth. This is especially important with ported bits, where the port may rotate harshly against the roof of the horse's mouth. Some (mainly English curbs) may have a lip strap to prevent the horse from chewing at the shank. Some bits will have a strap, wire, or chain that connects the bottom-most rings on the shank, called a hobble, to prevent the shanks from spreading too far or being pulled together. These keep the shanks more stable.
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Curb Bit Styles
There is a huge variety of curb bit styles, both English and Western, but the principal actions are the same for both. The cheekpieces, come in many different styles (shanks and purchase) and lengths. The different mouthpieces and cheekpieces affect the action and severity of the bit.
Cheeks may be straight or curved, and the shape of the cheekpieces affects the leverage action. The cheekpieces may be solidly attached to the mouthpiece or may swivel. Cheekpieces may be straight, slightly curved, almost half-circular, or S-shaped.
Some curb bits may have a straight mouthpiece, while others may have ports, keys, rollers or different types of materials and combinations of metals. Ports provide room for the tongue and, depending on the design, may act on the horse's palate. Spoons are similar to ports in that they are solid and act on the roof of the mouth more assertively.
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Curb Bit Materials
Various metals such as copper or sweet iron (rust) are thought to encourage the horse to salivate, resulting in a more responsive mouth. Various synthetic mouthpieces are designed to make the bit more comfortable for the horse. Jointed mouthpieces increase the pressure on the bars of the mouth with a nutcracker action when the reins are used. A common example of this is the Tom Thumb, often erroneously referred to as a snaffle bit.Continue to 5 of 5 below.
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Range of Severity
Curb bits can range from very mild, such as the very short-shanked kimberwicke (kimblewick), to very severe, such as a high-ported long-shanked correction bit. The severity, however, is not in the bit itself but how it is used. In the wrong hands, the mildest snaffle bit or shortest shanked curb can be very severe.
Excessive pulling and jabbing can be very painful for the horse, resulting in behaviors such as head tossing, rearing, rooting, and balking. Eventually, your horse will become numb to the bit and difficult to control.