That's a play on words. Last night I had to make a somewhat urgent 360 mile round trip to Oregon. I experimented with trailing semis. Not as close as would truly be drafting, but close enough to try to let them part the air for me. I could tell a difference on my SGII. I couldn't do it the whole time, and circumstances prevent a true experiment. Having said that, I found that about three truck lengths back I could bleed to a lower GPH and TPS, while MPG went significantly higher. The down side of this is I spent the whole time trying to anticipate what to do if the truck hit its binders.
I recently tested out some semi-drafting too. I noticed that even at two to three car lengths (much more space than most people keep in Michigan) I was getting MUCH better mileage in my parents' RX400h. I was actually a bit shocked as to how much my gains were. I would typically jump from about 28-30 to 38-42 simply by sitting behind semis. I still prefer to have more than two to three car lengths of braking reaction time though, so I didn't do a lot of drafting on that trip.
Now if I were driving a light car with excellent brakes on it...
Anyways, the gains ARE THERE, and as long as you are smart in how you do it, semi-drafting can be a safe and beneficial practice. Just be careful out there.
At normal following distances, 2-3 seconds, it feels like it's worse to be behind a tractor trailer. I drive a civic and the turbulant wind just pushes me around. I never notice a speed decrease when I pull into a different lane either. The only way for me to notice a decrease in power is if I am right on his bumper, within 2 car lengths, which is not comfortable because you have to be so attentive. I rather have clear open road in front of me and enjoy the scenery and not have my car pushed around.
But I did drive my friends Cherokee on the highway once and did notice a difference when following trucks. I suppose it helps a brick a lot more than a reasonable aero car like my civic.
I would never draft a semi. Not just because of the risk involved to one's life, but also because trucks with huge tires like that are prone to kick up rocks and other debris which can crack windshields and leave dents and scrapes on a car's paint.
I highly doubt that any semi driver would assist you in drafting. Especially if it's close. Even if he doesn't mind not being able to see you, being in his vacuum trail may drastically increase your FE, but it decreases his.
So you're saving gas by wasting his. By catching his slipstream, and continuing it on unbroken over your car, you're increasing the size of the dragging vacuum bubble behind him. You get pulled forward with ease, but he's drug back.
So really not that nice to do, in any way whatsoever...
Long distance drafting, though, where you're just in his wake, where the air is turbulent enough it's easier to cut through it, rather than his slipstream, I do try to do that when I can. And that's safe enough not to worry, easily past the 2 second rule.