ANSWER:
The port of the curb bit provides room for the horse's tongue. As the tongue
absorbs or cushions some of the bit pressure, a high port decreases this
option, making the action of the bit on the bars more direct. In other
words, the higher the port, the more careful the rider has to be with his
hands.
The curb bit does not exercise any pressure on the poll. The severity of the
bit is determined by several factors such as thickness of the bit, height
and shape of the port, ratio of upper to lower levers, the angle of the
levers, as well as the tightness of the curb chain. Since there are more
factors involved in the design of the curb than of the snaffle, there is a
larger variety of possible bits - although the tack makers don't seem to
make use of it to the same extent in the design of curb bits as in snaffle
bits.
The curb chain determines the angle of the curb bit to the horse's mouth.
The correct angle is 45 degrees (when there is contact on the reins). If the
angle is larger, the lever action is greatly diminished, and the bit becomes
ineffective. In equestrian terms, we say: "The curb falls through" (Die
Kandare faellt durch). If the angle is smaller than 45 degrees, the bit
action loses its elasticity, and the leverage becomes too severe. The German
term is: "Die Kandare strotzt". I have not yet heard of an English
equivalent yet.
The double bridle has evolved over the centuries beginning with a curb bit
with *long* shanks and very interesting bit shapes, via a combination of
curb bit and cavesson, to the modern combination of snaffle and curb bit.
The reason why two devices have been found useful in practice is that the
curb's effectiveness is unparalleled when it comes to flexing the haunches
and the poll. But its usefulness in supporting the seat and leg in achieving
the lateral bend is extremely limited. The cavesson with its action on the
horse's nose, and the snaffle bit, both are much more effective in achieving
lateral bending, lateral suppleness (of course only in conjunction with seat
and legs). They also have an elevating effect on the horse's neck, whereas
the curb tends to have a lowering effect.
Together the curb and cavesson or curb and snaffle bits with their possible
combinations multiply the variety of possible rein aids exponentially. They
open the door to an extremely sophisticated, differentiated, and versatile
communication with the horse. The double bridle tends to have a bad
reputation due to the countless excesses in which crude, uneducated riders
(up to the Grand Prix level) abuse it to force the horse into a headset.
The question when to introduce the horse to the double bridle finds
different answers in the different equestrian cultures. In Germany, the
double bridle is introduced at the end of the elementary training (Klasse L,
the equivalent of US 2nd level), since the soldier's horse had to be ridden
with a double bridle in all three gaits in formation. This coincides with
the beginning of collected work in a narrower sense.
In France and on the Iberian Peninsula, the double bridle is often
introduced sooner than that. James Fillis, who stands in Baucher's
tradition, even started green horses in a double bridle.
In the US, the double bridle is introduced in the competitions at 4th level
(the equivalent of the German Klasse S), which is essentially an
acknowledgement of the overall poor quality of the riders' education rather
than derived from any training-related necessities.
- Thomas Ritter
Question & Answer Forum
Last Update: January 13, 2007