15 meter circles
The next circle size you'll encounter in United States Equestrian Federation (USEF)
dressage tests is the 15 meter circle. These are found in First Level
tests.
The most common rider error seen in 15 meter circles is beginning the
circle as if it were a 20 meter circle. The rider will ask the horse to
leave the arena rail on the shallow turn that's appropriate for a 20 meter
circle. Then, about a quarter of the way through the circle, the rider
sees she's not going to make it, and pulls the horse off his feet to
complete the turn.
Fifteen meter circles that begin on the long sides of the arena reach to
the opposite quarterline. Check your arena
map if you don't know where the quarterlines are.
If you'd like, you can find landmarks to help you find the widest spots
on your circle, but that gets a little complicated. When you're starting a 15 meter circle from the long side, if you can aim for
the opposite quarterline, and then return to the rail at the letter where
you began, you can feel certain that your circle was pretty round
(barring potholes and unplanned exuberance on the horse's part).
* * *
15 meter circles at A and C are really tricky! The sides of your circle must touch a spot halfway between the wall and the quarterline (if you try for quarterlinetoquarterline, you'll be doing a 10 meter circle, right?).
