When I was a kid slip streaming on the race track was a big thing but the following car had to be within feet of the leader. The tchnique was to use slip streaming for the first part of the straight to gain a few extra MPH and then pull out and use those MPH to get past. I was astonished recently to learn that Formula 1 cars are now affected by the wake turbulence of a car ahead of the by up to three or four seconds. (They use a lot of aerodynamic down force and in turn create substantial turbulence.)