Racing is one of the oldest genres of video games and winning depends upon course knowledge as much as maximum speed through every turn. It's what enables maximum speed through each turn, frankly. In a rally race like DiRT Rally that's where the co-driver comes along.
DiRT Rally, which just launched out of Steam Early Access (uphill into a left 4 open half long — did I get that right?) provides drivers with a co-pilot calling out the turns to help manage the course. It's authentic to rally racing lingo, which means you may need to brush up on it before jumping in. Codemasters has a post explaining it here.
Basically, any turn that's an angle greater than 90 degrees gets designated one through 6, in order of sharpness. "Square" means a 90 degree cut, "hairpin" means what you think it means and "acute" is even sharper than that.
The vocabulary goes deeper, with warnings for tricky passages ahead or cautions for bumps and jumps. Codemasters put its voice actor, helmeted, in a motion chair to deliver extra authenticity in his dialogue, so that when he's calling out the next bump, it sounds as though he's feeling the first.
Rally racers, video game or otherwise, know that a co-driver is absolutely critical to top performance. Your adversary is not another driver, it's the course itself. Forza Horizon (the original) had co-driver dialogue in its excellent Rally expansion, too, so this is not an entirely new concept, but hearing a co-pilot stammer his words as he bounces alongside you increases the sense of immersion.
DiRT Rally hit Early Access at a $31.49 price earlier this week, offering 17 cars and 36 tracks. Codemasters plans to roll out new content, including the Pike's Peak Hill Climb, over the next six months.