Originally Posted by Brian B-P
It's a great video to illustrate some of the effects of load distribution... but it's not about weight-distributing hitches at all. It's from a British company, and WDH is very rarely used there.
Oops... I realized when I looked at this again that this specific video is something from the U.S., not the original by Bailey of the U.K. The idea is the same - mass distribution matters.
The rig in both cases has a moveable axle, so different trailer geometries can be simulated. The two posts holding the weights can also be moved, so it can be used to show that a trailer with mass closer to the ends is less stable than one with mass closer to the middle, even with the same tongue total mass and tongue weight. The video with the Mustang does not show the effect of axle position, or of moving masses toward or away from the middle.