A curb bit is a bit without any joints, if it is then it really is a combined
bit. The bit is made to create vertical flexion (up and down effect), as opposed
to the snaffle which is made for lateral flexion (side to side effect).
It is designed to help set the horses head in the position you want it, and
should be used with neck reining and not direct rein pressure.
For the bit to function the way it initially was meant to do it is important
that it is attached solid on the sides with no movement. This gives the bit the
stability it needs to avoid the problems that the combined bits have, which I
will write more about on the combined bits page.
The curb bit is constructed so that when you take a hold of one rein it
should give pressure on the opposite side of the mouth, and it is the stiffness
of the bit to allows this.
When one takes a hold of both reins the shanks gets pulled back, and this
causes the curb chain to tighten under the jaw of the horse. Therefore the chain
under the jaw of the horse makes a difference in the severity of the action. the
thinner the chain, the sharper the pressure is from it. Some uses a leather
strap under the jaw instead of a metal chain, and this is much more comfortable
for the horse.
In addition the bit gets pulled upward so that it creates pressure on the
poll. The bit also gets twisted backwards in the horses mouth, and applies
pressure to the horses tongue and bars.
If the bit has little or no port it will provide a lot of pressure on the
tongue and will therefore be a sharp bitt. But too much port is just as bad.
Some curb bits have such a high port that the bit will come up into the roof of
the horses mouth and create pressure there as well as the bars.
Some of them are made so that the tongue gets trapped, and others have
rollers in the port that will prevent this. The rollers are originally made to
make it more comfortable for the horse, but even this has been turned into a
tool for severity – some of the rollers are made sharp on purpose to affect the
horse even more.
The curb bits vary a great deal in severity, this is decided by all the above
mentioned factors and also by the thickness of the bit, and the length of the
shanks. The shanks works like a crowbar, the longer the shanks, the greater the
leverage. Even with a very light pressure one can apply a lot of force on the
horses mouth if the shanks are long.
If the bit is not made harsh in itself, and the rider has good hands and uses
neck reining, the curb bit can be very comfortable for the horse. But it is
important not to use this bit as a break or a power tool.
