A number alone isn't enough. Your co-driver uses modifiers to tell you how to take the corner. If you were looking for a PDF to print out and keep by your wheel, copy-paste this section!

The first few corners were clumsy. The notes felt absurd—calling out "crest" for a bump in a real gravel road, "6 Left" for a bend that looked like a 4. But then, around the third mile, something clicked. The notes weren't describing the road he saw . They were describing the road his father had felt . The rhythm of it. The flow.