Understanding load leveling

Without a load leveling hitch, a tow vehicle may be ‘squirrely’ because the steering wheels are being lifted off the road. The headlights may also be lifted to shine into the eyes of oncoming drivers. The weight effects of the trailer tounge may also cause the rear axle to be overloaded.

When you hitch a trailer to a car it is like putting a weight on a see-saw. The trailer tounge pushes down on the rear bumper, the rear axle acts like a fulcrum, and the front of the car lifts. If the rear axle to bumper distance was long enough (the lever arm) and the trailer heavy enough, it is even possible to lift the front wheels right off the ground!

A load leveling hitch works against this leverage by stiffening the hitch point. If the bumper doesn’t go down, the front of the car can’t go up. The mechanism adds what engineers call torque or bending moments to the hitch. This is like having very strong hands grabbing the hitch on either side of the trailer ball and twisting each side to force the ball upwards.

There are four places of connection to make this twisting. These are two pairs (two hands) of connections that each provide leverage that generates torque. One hand is represented by the ball mount, shank, and receiver to provide torque to the tow vehicle. The other is defined by the ends of the spring bars at the ball mount and the attachment to the trailer A frame. But all this can be boiled down to two points at the spring bar connection in the final analysis. The spring bars and hitch assembly transfer the forces out to the truck and trailer.

Spring bars are used to provide some elasticity to the hitch stiffening. This is done for the same reason you have springs on your car wheels. Like springs without shocks, you can get some bouncing if the road bumps the rig just right. This bouncing is called porpoising.

The model is that of a loaded beam and how it resists bending. The load leveling hitch developes torque at the ball mount where the trailer tongue load is located. The twist is conveyed to the tow vehicle to lift its rear via the shank and receiver. The twist is conveyed to the trailer via the spring bars to lift its tonque. This twist is accompished by a force acting over a distance which is normally known as torque.

The key is how the spring bars are attached to the ball mount. The ball mount, shank, and receiver are the ‘fixed’ parts. The spring bars have a mount that is rigidly attached to the ball mount. That is rigid in terms of up and down but quite flexible in terms of side to side. So the mount usually has several inches of steel up and down and a rotating mechanism for side to side – like a very strong hinge.

What you really have is the same kind of considerations you would have for a beam supported on each end with a load in the middle. How does it keep from breaking under load? What makes it stiff and resists bending? Same thing with a hitch, just a slightly different mechanism.

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