I have to admit, I don’t know a lot about driving bits. They look quite intimidating and bulky to me, so researching this topic will be interesting. There seems to be a variety of different cheekpieces available, with a large range of mouthpieces, just like bits used for riding horses.
The most traditionally used driving bit is the Liverpool. This bit offers a wide range of rein positions, which dictate the contact severity. It can be made in a variety of mouthpieces also, with fixed or swivel cheeks. Fixed cheeks do not allow the cheeks to swivel and are designed to be used with a pair of horses. This avoids the pinching of the lips that can occur with the coupling reins. With swivel cheeks, the mouthpiece can be made to slide up and down. A sliding mouthpiece is often preferred, because it tends to keep the mouth more responsive. Accompanied by a curb chain, the Liverpool bit offers a variety of rein settings for maximum adjustability.
A long lower shank in relation to the upper shank (or purchase) increases the leverage, and thus the pressure, on the curb groove and the bars of the mouth. A long purchase in relation to the lower shank increases the pressure on the poll and chin, but does not apply as much pressure on the bars of the mouth. A longer purchase will also lift the cannons up and cause significant lip stretch, with an increased danger of dragging the cannons of the bit into the premolars.
A horse has more warning or pre-signal, in a long-shanked bit, allowing it to respond before any significant pressure is applied to its mouth, than it would in a shorter-shanked bit, but ultimately it is the straightness or curve of the shank, which translates to the abruptness of response.
A straight shank, following the line of leverage, will produce a faster response in the mouth and curb than a shorter curved shank. In this way, a longer shank can allow better communication between horse and rider, without increasing severity. This is also directly dependent on the tightness of the curb chain. Pre-signal is everything that happens before the curb strap engages, so a properly adjusted curb strap is paramount in determining the amount of rotation and the timeframe a horse has to prepare for the bit to engage. Too tight and the action is abrupt and severe; too loose and the action is slower, but the bit rotates further, causing it to lift in the mouth and hit the premolars. Keeping this information in mind will help with deciding the position of the reins. The first and mildest position of the reins on the Liverpool bit is called Plain or Smooth Cheek. The bit is pulled back and up into the mouth and the curb chain is not engaged. If you need a little more reaction and communication, then Rough Cheek is the next option. This allows slight curb action, while the bit is pulled back in the mouth. First Slot position provides moderate curb action, as well as poll pressure and would be used for more enthusiastic and strong horses. Second Slot or Middle Slot gives increased leverage, pulling the bit down in the mouth, so that the tongue and lower jaw are pinched between the mouthpiece and the curb chain. Poll pressure is also created. Finally, and not a position for the faint of heart, is the Third Slot or Bottom Slot – which exerts maximum poll and curb pressure. This severe rein setting should be used only as a last resort in a crisis. It is also known as “Dead Man’s Slot”, because if you are in the bottom slot, you have nowhere else to go!
With any type of bit selection, be it for ridden work or driving, it is always important to know your horse – any bit can be severe and cause damage in the wrong hands.
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