Dwyer on Curb Bits—Part III
Now we get to the outside of the curb bit, the upper and lower bars of the curb bit cheek-pieces. Again all quotes come from “Seats and Saddles, Bits and Bitting” by Francis Dwyer, all caps are my emphasis and all parentheses include my clarifications when the meaning is unclear.
From page 162-163-- “The first question that naturally presents itself is, the absolute length of the lever—that is to say, of the upper and lower bars of the bit taken together; the next, that of their relative proportion to each other. Before going into the consideration of these...namely, that a bit may be regarded as a pair of levers connected together by the mouthpiece. At first sight this might lead to the conclusion that THE CENTER OF THE RIVET ON EACH SIDE IS ALWAYS THE POINT FROM WHICH THE LENGTH OF THE UPPER AND LOWER BARS IS MEASURED. This is, however, only true for those forms of mouthpiece which consist of a port and two lateral straight portions; but if THE WHOLE MOUTHPIECE FORM ONE CURVE, the line of bearing—that is to say the line connecting the the two points of the mouthpiece which rest on the bars of the horse's mouth—does NOT coincide with the axis of the bit passing through the center of the two rivets, which must be taken into account in estimating the relative lengths of the upper and lower bars of the bit (this applies to Mullen mouth curbs as well as those with a bigger curve in the mouthpiece.)
The measure for the length of the upper bar of the bit, taken from the “line of bearing” to the point at which the curb-hook acts, is the height of the bars of the horse's mouth, which...is pretty nearly a constant quantity—namely, 1.8” English inches, decreasing with very small horses and ponies to 1.6” English inches; therefore...we may say that 1 3/4” inches is the proper length for the upper bar—very seldom less, and hardly ever more.”
“If one put a (curb) bit into a horse's mouth without attaching a curb (chain) to it, when the reins are drawn the bit turns right round, and its bars or branches (cheek-pieces) come to lie in the same line as the reins. There is no lever action whatever, because there is no prop, and a snaffle or bridoon would, on account of their center joint, be much more efficient. The same thing too, will happen if THE CURB (CHAIN) BE VERY LOOSE: the bit is then said to “FALL THROUGH”--in fact, it is nearly useless.
The opposite fault to “falling through” is when the bit “STANDS STIFF” without any play, the slightest pull of the reins causing the horse great pain, and, most probably, just in the wrong place externally; for this stiffness or rigidity of the bit is very often produced by a TIGHT CURB (CHAIN), and therefore the horse, instead of following the rider's hand, pokes against it. Good bitting will be equally removed from stiffness and falling through: it lies between these two extremes.
Page 163-164 “The length of the upper bar of the bit will, however, of itself cause this instrument either to stand stiff or to fall through, if it exceed or come short of the height of the bars of the mouth.
(Exceeding the height of the bars of the mouth) it will be stiff , and the curb (chain) acting upward (along the horse's lower jaw), will press on the sensitive part of the jaw (it no longer lies in the curb groove and rides up on the sharp lower jaw bones.)
On the other hand, the bit with the short (less than the height of the horse's bars) upper bar, will FALL THROUGH. The curb (chain) will, no doubt, remain the the chin-groove, and act forward (toward the mouthpiece of the bit), but forming a very acute angle with the branches of the bit itself, will have scarcely any value as a prop. The lever action, however, will be very great, the lower branch being to the upper one at a greater ratio, 4 to 1.”
Page 165-- “(When the upper bar is equal to the height of the horse's bars) it will neither be stiff not fall through: the curb (chain) will remain in the chin-groove, acting obliquely forward, and will afford a sufficient prop of support; and the lower branch of the lever (hopefully) being in the proportion of 2 to 1 to the upper one there will be sufficient lever action.
It will be now easy to understand how it comes that people, in order to prevent a bit with a very short upper bar falling through, are driven to using a very tight curb (chain), the result of which is, that the whole action is transplanted from the interior of the mouth to the chin; as also that, in order to prevent one with a very long upper bar standing stiff, they use a very loose curb (chain), the result of which is, that the whole action is transplanted from the interior of the moth to the chin; as also that, in order to prevent one with a very long upper bar standing stiff, they use a very loose curb (chain), which has the effect of making the bit fall through; and this—an intensely long (wide) bit—is pulled up as high as it will go into the horse's mouth, and then a loose curb (chain) attached, and this...of course not only falls through, but acts nearly altogether on the exterior of the horse's jaw.”
Page 166-167-- “Now a very long lower bar, or a very low carriage of the horse's head..., will always have the effect of bringing the rein to act on the bit at an unfavorable angle;...If the inventors of these frightful bits (very long lower bar) had any real knowledge of the laws of mechanics and the applications of lever power, they would have found that the same amount of useful action would have been much more certainly obtained by a much shorter lower bar, without incurring the very serious disadvantage of lifting the bit in the mouth, which always must have the effect of causing the curb (chain) to mount up out of the chin-groove, and therefore produce conflicting impressions, tending to neutralize one another and puzzle the horse. Moreover, the longer the lower bar the greater will the space through which the rider's hand has to move in order to produce a given amount of action. It will be therefore slower, although more powerful, and consequently more unequal, rendering it very difficult for the majority of riders to hit off exactly the precise amount of pull required.
Having thus arrived at the conclusion that the absolute length of the lower bar should be diminished as much as possible, and also laid it down as a rule that a length of 1 3/4” is in all cases sufficient for that of the upper one, it is not difficult to ascertain what the relative proportions of the two should be, which would, of course, give us the absolute length of the former. And there we encounter the only useful general rule that bit-makers in general seem to be acquainted with—namely, that the the lower bar should be twice as long as the upper one, which, increasing the lever action in the proportion of three to one, should be under all circumstances ample. But the bit-makers, although adhering to this proportion, but too frequently make the lower bar inordinately long, because they have no standard of length for the upper one; whereas , if we adhere to the rule laid down above of 1 3/4” for the latter dimension, we have 3 1/2” for the former one, both measured from the line of bearing (center of the rivet), and 5 1/4” for the entire length of the bit measured from the point at which the curb-hook acts above (down) to that where the lower ring acts below. This will be the maximum required, and will be found sufficient in all cases; with very small horses or large ponies the upper bar will have to be reduced to 1 1/2”, the lower one to 3 inches, leaving the total equal 4 1/2”, which will be about the minimum.”
Most curb bits available now are not of the correct dimensions, dressage, Saddle-seat or Western, as I found out when I measured the fifteen curbs that I own for the three types of riding.
Have a great ride!