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I hesitate to even comment but here goes:
I think Mythbusters is right and their numbers are probably valid. Once upon a time on motorcycle I got behind a horsetrailer with horses in it- the ultimate draft vehicle because horse trailers are close to the ground (unlike that semi and trailer), have a large rear x-section, and because when horses are in them the driver is going to be extra careful and avoid sudden speed and lane changes unless it's really an emergency (unlike semi drivers who might swerve or lock up their trailer brakes to shake off a tailgater).
There was very little traffic but I got in "the bubble" undetected by the driver (I'm pretty sure) and hung out in there for a looooong time (150 miles at 75 mph!). I noticed that when I pulled in real close- maybe not 2 feet but... let's just say not far from that- I had to back off the throttle some and the temp gauge suddenly shot up. Bike had no windshield and I had my visor up- amazingly calm back there, not even the expected turbulence and buffeting. I didn't stay that close for long because the temp gauge climbed up against the red, I clearly heard the fan kick on, and I was sweating bricks too, so backed off enough to feel airflow again and see temp gauge go down. Still, at that point (I dunno- 25'?) much much less air to punch through than non-drafting although it was buffety and turbulent and unpleasant besides. Got way better mpg that tank even though cruise speed for that 150m was 20 mph faster than I usually go and also that segment was only part of a tank. Sorry, even though I calculated fe at most every fill, I didn't keep fe logs on the bike back then so I won't quote an exact value but yes it seemed to be a better than 40% improvement. Yup, it definitely works.
That was years ago and that was also the last time I took chances drafting even though there was no incident whatsoever. The chance of an incident is extremely high and I'm not suicidal these days... but sometimes we do stupid things in the name of science right??? Also it seems potential draft vehicles are never going the speed I want to go anyway. Seems like they are always kicking up rocks and gravel too. I don't draft (unless following using the 2 second rule counts as drafting) and don't recommend it.
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