One car tucks in behind another. Two cars can go faster than one. They divide the air resistance between them.
10 seconds sound clip from the Days of Thunder movie soundboard.
You can hear this line at 00:59:13 in the Blu-ray version of the movie.
Quote context
[...]
- How could you ignore me like that?
- I wasn't ignoring you. I gave you a very thorough physical.
- You're not gonna do anything weird on my leg, are you, Cole?
- No. It's just something Harry and I work on together. It's called drafting.
- Now, here's where it gets interesting.
- You and Harry work on that, huh?
- Yeah, right. Is there anything you want to do besides racing?
[...]