Why do passing trucks suck instead of blow?

Thanks for the responses, folks. As an aviation enthusiast and RC airplane pilot I am familiar with Bernoulli's principle; I just didn't make the leap to its application here.

Vulcan Rider wrote:

Dick_B wrote:
Nope, you are all wrong.
The real explanation is that the truck IS pushing air against the sides of the trailer and tow vehicle. BUT the least stable part of that assembly is between the trailer wheels and the hitch. When that part of the assembly is pushed away from the truck it tends to also move the back of the tow vehicle away from the truck which tends to turn the front of the tow vehicle TOWARDS the truck thus giving the impression of the truck sucking in the tow vehicle.
You're welcome.

BINGO.

But look at the little picture that the OP provided in his post.

The high pressure wave near the front of the overtaking big truck first pushes against the back of the TT; that tends to push the back of the TV closer to the semi. Just about the time you correct for that, the pressure wave contacts the front of the TT and the back of the TV pushing it in the opposite direction.....which is the same way that your correction was going.

The dynamics of a one piece unit, like an A or C is a bit different but the same basic principle still applies. If your front end is worn or out of alignment, the effect is MUCH worse.

There isn't much you can do about it.......except maybe to minimize the speed difference if you can. This is just one of the reasons that I prefer NON-Interstate/Freeway roads; almost no big trucks.

In my case I'm afraid you're both wrong. My ProPride 3P hitch eliminates sway, so the entire rig gets pulled in towards passing trucks.