Drafting semis does work, however here they pour gravel on the roads in winter, not salt, so if you draft a semi, you get a free sandblasting job on the front of your car. So I don't draft the semis. However I did try it once in my 87 daytona. The onboard mileage computer has an instantaneous MPG display and IIRC getting in behind a semi bumped it up by nearly 10mpgs.