Dwyer on Curb Bits, Part I
Dwyer writes a lot on curb bits because back then the cavalries used a lot of curbs, either by themselves or as part of the double bridle. From his experiences with 400 light cavalry horses in the Austrian Imperial cavalry he determined that many, if not most, of the problems that the cavalry troopers had with their horses came from improperly fitted and sited curb bits.
Dwyer (and Oeynhausen) found certain ratios in the horses' heads that dictated which curb bit and where it was in the horses' mouths, to be the most comfortable for the horses as proven by the improvements with these horses when their wrongly sized bits were changed to properly fitting bits. There were three main differences in these horses' mouths that directed the selection of the proper bit, as well a the universally dictated proper position for the curb bit in the horses' mouths.
Before I get into the nitty-gritty of the measurements this statement of Dwyer's points out the most important consideration: on page 134 "the curb (chain/strap) has one fixed position in the chin-groove, and this governs the whole arrangement." The curb chain only works properly when it is in the chin-groove, if it goes over the sharp bones further up the lower jaw it can become intolerably painful to the horse, AND the too high and painful curb chain encourages the horses to stick their noses out front instead of coming into a proper position for collection.
Still on page 134, "There are three dimensions of the interior of the horse's mouth which must be accurately ascertained before attempting to fit him with a proper (curb) bit, in addition to certain details connected with the tongue.
The first, and a very important one, is the transversal width of the mouth, from side to side, measured at the same height as the chin-groove, and including the thickness of the lips...This gives the width of the mouth-piece, which must be made to fit exactly, as, if too narrow, the lips are subject to injury and their being displaced so as to cover the bars, thereby neutralizing the action of the whole instrument (curb bit + curb chain); whereas, it too wide, it slips from side to side and displaces what is termed the port--the curved portion of the mouth-piece intended to moderate the pressure on the tongue--from its proper position; it also determines the length of the curb (chain).
The second dimension is the width of the channel in which the tongue lies, or the distance between the two bars internally, which determines how much of the mouth-piece may be allowed for the port; the remainder must be reserved for the action on the bars."
"The third dimension what we term the height of the bars--that is to say the distance between a straight edge supposed to rest on the upper surface of the bars...and another straight edge placed exactly parallel to it, touching the undermost point of the chin-groove--mathematically speaking, the tangent to the curve formed by the groove. This later dimension--the height of the bars--is, perhaps, the most important of all, because all the remaining dimensions of the (curb) bit must be deduced from it."
Page 136--"Lieutenant-Colonel von Oeynhausen says that the height of the bars is 1.81 English inches with the very great majority of horses, and that it is unusual to find it either more or less. (My note, remember these are cavalry horses or horse artillery horses, tall enough to carry a cavalryman in battle or big enough to pull heavy guns, not ponies or super delicate Arabians.) The author (Dwyer) has certainly never found bars that exceeded 1.8 English inches in height, but he has seen some that were less--perhaps about two to three percent of the horses he has had to do with. Now this is a very important dimension , because the upper bar of the bit (my note--from the center of where the mouth-piece is attached to the cheeks of the bit up to where the curb hook hangs from the upper ring of the curb bit) should never exceed the height of the bar of the horse's mouth...it is only necessary to go into any saddler's or bit maker's shop to satisfy oneself that a very large proportion of (curb) bits, even of those intended for saddle-horses, are constructed in total defiance of this rule, and calculated for animals that have much higher bars, wherever they are to be found. (My note, after measuring the 12 modern Weymouth or cavalry shanked curbs in my collection THIS IS STILL TRUE!!!)
On page 137--"The width of the channel for the tongue, or lingual canal,...is pretty nearly always three fourths of the height of the bars; and this being very constantly 1.8 (English) inches, the other (lingual canal,) will be found to be about 1 1/3 inches (English inches)...which gives us the dimension of the MAXIMUM WIDTH OF THE PORT OF THE BIT (my caps), where there is one; because, supposing the mouthpiece to have exactly the proper width, if the port be made wider than the lingual canal, its corners will come on to the bars of the horse's mouth and produce intolerable pain, which once and for all, is wholly inconsistent with good bitting; and this is precisely the reason why it is of so great importance that the width of the bit should coincide so accurately with that of the horse's mouth; as, if it be too wide, and a port exists, every pull of the rein will be sure to bring its angles into painful contact with the bars on one side or the other."
Leaving Dwyer for now I am very happy to say I got to ride a horse this week, finally, since my ribs have had a chance to heal. Debbie put me up on a horse, Cinnabar (a half Arab/ASB Mustang cross) a grey gelding around 15 to 15.1 hands high. I just walked. I was trying my D-ring "anatomic" single jointed titanium coated snaffle, and both of us agree that Cinnabar DOES NOT LIKE "anatomic" (super curved) snaffle bits at all. Cinnabar was not happy at all about not being out with his friends frolicking in the pasture, he did not like the bit, and he was not too certain about my bad balance, in-coordination, and sort of uncertain hands. I had Debbie ride him first for a few minutes. Cinnabar had some problems stopping promptly from my hand aids, hopefully he will be better with a bit he prefers. He promptly gave me a turn on the hindquarters and a turn on the forehand so he knows what a single leg means. He did the regular gradual turns weaving around the fences fine. All through the ride he was "muttering under his breath" about all his buddies having fun in the pasture while he had to put up with me. I kept him pretty near to Debbie the whole ride because, after my fall, I confess I am a little timid right now on a new horse.
Have a great ride!