Horse Bitting - Curb Bridles and Curb Chain Tighteners

Horse Bitting – Curb Bridles and Curb Chain Tighteners

“You never stop learning about bits and bitting; every horse has a varied/individual response which adds to the knowledge base.”

Click here for an introductory lesson on bits and bitting.

Specific riding disciplines use one type of bit more than another. For example, stock seat horses are ridden mostly with curb bits, with riders placing one hand on the reins and no rein contact on the horse's mouth unless applying a specific cue. Conversely, hunt seat horses are ridden mostly with ring snaffles and guided with two hands on the reins and continual light rein contact with the horse's mouth. Bit selection will also vary because of differences in the abilities of horses and riders.

A curb bridle places pressure primarily on the mouth and curb with leverage pressure from the reins. Sometimes curb bits are termed a snaffle if they have a jointed mouthpiece, however, curb bits work differently by leverage or curb pressure whilst a snaffle works by direct rein pressure to the mouthpiece.

A curb bit is constructed with a mouthpiece and shanks. The headstall is attached to upper shanks and the reins are attached to lower shanks of a curb bit. A curb bit applies leverage pressure and, as such, increases the amount of pressure from the reins to contact points in and around the horse's mouth. In general, curbs are designed to be used with no rein contact unless the rider is applying a specific cue.

When reins are pulled, the action of the mouthpiece and curb-strap tighten on various locations in and around a horse’s mouth. Curb bit construction is modified to apply varying amounts of pressure on the tongue, lips, bars, roof of the mouth, and, by way of the chinstrap and headstall, under the chin and over the poll on the horse’s head.


Curb diagramCurbs are used primarily to slow or stop horses with pressure created by leverage and to guide horses by using a neck rein cue. A neck rein is a slight rein cue applied to the neck of the horse more so than to the mouth. The neck rein does not apply an appreciable amount of pressure to the horse's head or neck and does not forcibly turn the mouth to the direction of the desired movement. Rather, the correct response from a neck rein occurs as a learned response from reinforcements with direct pull or pressure on the horse's mouth. Curbs are used on horses trained previously with snaffles to respond to direct and neck rein cues. Curbs with longer lower shanks in relation to upper shank length increase pressure by increasing the leverage of pull. Pressure is intensified on specific pressure points by variations in the mouthpiece design.

Mouthpiece variations:

Mouthpiece VariationsPressure is directed to specific pressure points by variations in the mouthpiece design. Mouthpiece diameter may be tapered to the center and typically varies from 5/16 inch to 3/4 inch, although there are smaller and larger sizes. The smaller the diameter of the mouthpiece, the smaller the contact in the horse's mouth. And the smaller the contact area, the more intense the pressure a horse feels from a given amount of pressure from the reins. Most mouthpieces are smooth and rounded. Some mouthpieces are twisted, rolled, or flattened to cause variations in the intensity of pressure.

More mouthpiece variationThe mouthpiece port is the raised portion on the centre of solid, or mostly non-hinged, mouthpieces. The port places pressure along the tongue and, if high enough, the roof of the mouth. Ports with 2 1/2 inches or more of elevation can apply pressure on the upper palate and, because of the sensitivity of this area, should not be used on inexperienced horses or by inexperienced riders. Wider port widths allow for less pressure on the tongue. Port shapes vary, including rounded, flattened, rolled, and covered. The top of the port may be flattened backward to heighten pressure on the tongue in the absence of rein pressure and to alter bit balance. Port heights and widths vary to allow for differences in the amount of tongue relief and pressure on the upper palate.

Mouthpiece-Shank JunctionThe mouthpiece-shank junction may be welded solid or be attached with a sleeve or hinge that allows some flexibility. Bits that are loose-shanked, sleeved, or hinged at the mouthpiece-shank junction allow for the initial part of the rein pressure to be exerted more gradually. This slight difference is termed signal.

The placement of the mouthpiece relative to its angle with the shanks will also affect how the mouthpiece lies in the horse's mouth. Mouthpiece placement usually varies from the port and upper shanks being aligned with one another to the port positioned forward of the upper shanks by about 20 to 30 degrees.

Over-balanced bit: Bits constructed to significantly release pressure when the rein pressure is released. Balanced or Under-balanced bit: Bits that maintain pressure without rein pressure.

Most bits are designed to be over-balanced because they release pressure when not cueing. Balanced bits are used infrequently and, then, only on experienced horses and by experienced riders.

Click here for more information on curb chains.

The curb chain is mounted in the chin groove under the horse’s chin between the bit shanks of the bit. It steadies the bit within the mouth (keeping it centered), and it controls the lever action of the reins. It keeps the bit shanks from the bit from over-rotating. The curb strap acts as an arm of a fulcrum, pushing the bit down onto the horse’s bars, amplifying the bit’s pressure directly onto the sensitive bars of the horse’s mouth. It also brings pressure up into the chin groove and “twists” the headstall down, causing downward pressure on the horse’s poll.

The curb chain is engaged when the rider moves from picking up the rains to “handling” the horse. When the reins are “pulled”, “the shank of the bit rotates back towards the chest of the horse and the cheek (upper shank) of the bit rotates forward (since it is a lever arm). The curb chain is attached to the rings at the end of the cheek, so, as the cheek moves forward, the chain is pulled and tightened in the curb groove. Once it comes in contact with the curb groove of the horse it acts as a fulcrum, causing the cannons of the bit mouthpiece (the bars) to push down onto the bars of the horse’s mouth, thus amplifying the bit’s pressure on the mouth.”

If the strap is too loose, it either doesn’t work at all or it slows down the action of the reins.

If it is too tight, it applies curb (chin) pressure from the reins as soon as the rider is on the reins, giving the horse no time to respond to impending movement instructions before uncomfortable pressure is exerted on his mouth. Common practice is to adjust the strap so that it comes into action only when the shanks rotates about 45 degrees back. This is usually about two fingers of space between the horse’s curb area and the strap. However, each horse is different, and that adjustment is not set in stone. The narrower the chain is, the more intense is the pressure to the chin groove. Generally, wider is better. Sometimes a curb chain has a buckle or hook attachment and English designs have a “fly link” in the middle to hold a lip strap.

Here are some basics about horse bits

Curb bit nomenclatureThe port gives relief to the tongue when the curb pressure forces the bit down onto the bars of the horse’s mouth. It allows the tongue someplace to go under pressure, slipping it up into the port space. A low port gives less relief.

Horse with ReinsAs the reins pull back toward the horse’s chest, the shanks rotate back and up until the curb strap stops the rotation. The pressure tightens the curb strap under the chin – effectively putting the horse’s lower jaw in a vise-like grip between the mouthpiece and the curb strap. The grip pulls the bit down onto the bars of the mouth.

“Signal” time: The time it takes between the rein cue and the shank moving far enough to engage the curb strap.

You may find the diagrams in this .pdf useful.


Here is an article on how bridle styles impact rein tension.

In a recent study, researchers in Germany determined that Western curb bits caused less rein tension than did English snaffles. They also found that one-handed riding is associated with more stable rein tension. “Considering relationships between horses’ muscular condition and rein tension appears important for equine welfare and has the potential to add further knowledge to investigations of horse-rider interactions,” Kuhnke said.

Here's more information on how a curb bit works.

Curb bits allow the rider to give much subtler rein aids than with many snaffles. They encourage a horse to flex and carry their heads on the vertical.

Because curb bits are leverage bits, your aids are magnified compared to the direct pull that activates a snaffle bit. Using a curb bit means you must keep your hands quiet unless you are using reins aids—your hands and body must move independently. Inadvertently jabbing on your horse's mouth with a curb bit, for example, if you lose your balance and use your reins to hold you up, could be very painful for the horse and cause training problems if it happens often.

Some curb bits may have a straight mouthpiece, while other 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. Similar to ports are 'spoons' that are solid and act on the roof of the mouth in a more assertive way.

Here's more information on Western curb bits.

A true snaffle bit has a 1:1 pressure ratio, meaning that for each ounce of pressure you exert on the reins, the horse feels one ounce in his mouth. The ratio of a normal curb bit can be determined by measuring the length of the shank and the length of the purchase. If you measure the length of the shank and get 4; then measure the purchase and get 1, then that particular bit has a pressure ratio of 1:4, meaning that for every 1 ounce you exert on the reins, the horse feels 4 ounces in his mouth.

ShanksThe straighter the shanks on a bit, the less warning the horse gets before the action of the bit is engaged because it takes less rein movement to move the shanks. This, in turn, usually makes for a slightly harsher bit because there is no build to full pressure, it just happens almost instantly.

Swept back ShanksOn a bit with a more swept back shank, there is more warning to the horse before the action of the bit is engaged because you have to pick up more rein to contact the bit. On a well-trained horse, they will feel the weight of the reins being moved and respond before the bit ever has a chance to move in the mouth. These are also commonly called a “grazing bit” because the swept back shanks allow the horse to graze while still wearing the bit.

Here's information on correct curb adjustment.

Correct curb (chin strap) adjustment on curb or leverage bits is critical for safety (stopping your horse) and is also important for proper function of not only the bit and curb but the entire bridle.

Curb adjustment imagesCurb adjustment is correct when the horse gets a signal from the bit as the reins are pulled (feels the bit begin to move) before the curb contacts the chin. For safety, be certain the curb makes contact when you pull the reins. This contact generally occurs within approximately 3 inches of pull on the reins or an approximate 25 to 30-degree change in angle of the shanks after pulling the reins. A good rule of thumb: you should be able to slip a finger or 2 between the curb and chin if adjusted correctly.

Always double-check before mounting by pulling the reins to see that the curb will make contact with the chin within 25 to 30 degrees of shank movement.