when does calliope get hit by the tractor?

From the text (Page 230)

The tractor had just made a turn onto the road.High in his seat, the farmer didn’t see me. I was looking back to check on Jerome. When I finally turned forward it was too late. Right in front of me was the tractor tire. I hit it dead on. In the terra-cotta dust I was spun upward into the air. At the apex of my arc I saw the raised plow blades behind, the corkscrewing metal covered with mud, and then the race was over.

This quote is from the chapter, The Gun on the Wall.