Hensley Hitch
A 4-Bar Problem






Hensley Hitch
Turning

I find the discussion of how the Hensley Hitch works to be fascinating. Back in engineering school, we called this a "4-bar problem". In the 4-bar problem, you connect the ends of 4 rigid bars together allowing them to pivot at the connection points.

The Hensley hitch is a 4-bar problem where the bars form a trapezoid. To create this hitch, you could put a receiver on the front of the trailer, similar to what is on the tow vehicle. Then put a "T" bar into both receivers, with the "T" in the trailer slightly wider than the "T" in the tow vehicle. Then connect the ends of the T's together with 2 equal length bars to form a trapezoidal 4-bar problem.

Initial rotation (turning) of the tow vehicle to the right moves the front of the trailer to the right because of this 4-bar setup. With the standard hitch, the trailer actually moves left initially (creating the sway condition).

Take a look at the diagram posted at:

http://www.divtune.com/hensley/

The apparent pivot point between the tow vehicle and the trailer is where their center lines intersect. With the Hensley, this apparent pivot point is moved forward of the hitch. The apparent pivot point will start at a fixed distance in front of the hitch which is the same for every Hensley. The more you turn, the more the pivot point moves backward towards the trailer. Trailer sway is produced by small amounts of rotation, so the slightly moving pivot point probably doesn't matter at highway speeds.

I think that the complexity and expense of the hitch comes from also including the weight distributing features of the hitch, which I haven't tried to show. I've heard that Hensley may come out with a cheaper hitch that doesn't include weight distribution. Hopefully, they'll include a class 2 version, since many lighter trailers that don't need weight distribution use class 2 hitches.

Bill Basham