The importance of tongue weight calculator

IN his presentation, Luis Vendrell, a mechanical engineer with U-Haul International, emphasized the importance of using a tongue weight calculator to ensure uniform trailer loading.

“It’s a basic set of equations that will allow trailer manufacturers to more easily design around that desired tongue weight,” he said.

“You can see where this would come in handy before you design a trailer so you can have these numbers in your head prior to even knowing what your design is.”

First, some definitions:

•  Tongue Weight (TW). Force, or weight, exerted on the tow-vehicle hitch-ball by the trailer coupler.

•  Effective Tongue Length (ETL). The longitudinal distance from the center of the hitch ball to the center of the suspension.

•  Mass Radius (R). The longitudinal distance from the center of the hitch ball to the center of gravity of the trailer’s load.

•  Center of Suspension (CoS). The center of the suspension is located at the center of the wheel on a single axle trailer. On a dual axle trailer, the center of suspension is located at the halfway point between the centers of the front and rear trailer wheels.

•  Uniform Loading. Assumes that the trailer is loaded to maximum cargo capacity at a constant density. This means that the load density does not vary along the length or width of the trailer.

On a trailer with an Effective Tongue Length of 100 inches, mass radius of 88 inches, bed length of 100 inches, empty trailer weight of 800 pounds, Empty Trailer Tongue Weight of 80 pounds, and gross trailer weight of 2500 pounds, the tongue weight is 284 pounds at a tongue weight percentage of 11.86%.

“If you have a giant box in front and a small box in back, you can do simple calculations to figure out where the center of mass would be between those two boxes, so obviously you would shift it further forward,” he said. “You would change the mass radius to where that new center of gravity lies. Let’s say its 60-40%. On a 100-inch tongue bed, it would be probably about 10% further forward, so about 90 inches.”

He said this calculator can also be used for boat trailers. ♦

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