Trailer Hitch

Connecting the trailer to the tow vehicle is the job of the hitch. From the trailer's point of view there is just one variable, the size of the ball. From the tow vehicle side, there are several variables to consider.

Hitch Coupler Ball

There are three common sizes of hitch coupler balls, 1 7/8-inch, 2-inch, and 2 5/16-inch. It is important that the hitch coupler on the trailer be matched to the proper size coupler ball, otherwise the latching mechanism may fail to retain the hitch on the ball. Safety chains should always be used to keep the trailer connected in the event the hitch separates. One thing to double check that is seldom mentioned: be sure the trailer hitch is firmly tightened and engaged on the ball. On level ground, gravity and the tongue weight will keep the hitch on the ball, but when backing down ramps, particularly ones with a steep descent, there may be a transition point as the trailer backs over the crest of the ramp. The tongue weight may become negative and the trailer will try to lift the hitch off the ball. Should this happen it would be disaster for your outboard or outdrive lower unit.

For smaller, lighter trailers, the 1 7/8-inch coupler ball is common, and it is used up to about 2,000 pounds of towed weight. This is known as a "Class I" rating. For towed weights up to 3,500 pounds, known as "Class II" rating, a 2-inch coupler ball is commonly used. A 2-inch ball can be used with loads up to 6,000 pounds, if special heavy duty hitch balls are used which have larger shanks. The "Class III" rated 2 5/16-inch coupler ball can be used with loads up to 10,000 pounds.

Vehicle Hitch

On the tow vehicle side of the connection, there are more things to consider. Back when cars had heavy chromed steel bumpers, a bumper-mounted hitch was common. These days, modern cars have bumpers unsuited for use as an attachment point for a hitch. The vast majority of hitches are mounted to the car chassis or frame (if there is one). The most common hitch is the "drawbar" type, which bolts to the car and provides a receiver pocket into which a steel drawbar for the hitch is secured. This has the advantage that the drawbar and hitch coupler ball can be removed when not in use. Again, there are several grades or classes of hitch, which should be used as appropriate for the towed load weight.

The drawbar can also incorporate lift or drop to position the coupler ball at the proper level for connection to the trailer coupler. Excessive lift or drop in the drawbar causes a de-rating of the hitch. Check with the manufacturers for details, but in general a 4-inch change is about the maximum permitted.

The drawbar can also be enhanced beyond being just a straight hunk of steel to have other features. One typical upgrade is to incorporate shock absorbing material into the drawbar, providing better ride quality to the passengers of the tow vehicle. Another option is to provide limited pivoting of the drawbar, which makes coupling it to the trailer much easier. This is especially important with larger trailers that are reluctant to move under "Armstrong" power.

Tongue Weight

Adjusting the tongue weight is part of the trailer rigging process and is discussed in a separate article

The target for proper tongue weight is about 10% of the total towed weight, and as that nears 5,000 pounds, the tongue weigh is approaching 500 pounds. Even the biggest vehicle will react to that much weight dropped on its extreme rear end. At these weights, a different type of hitch is recommended.

Weight Distributing Hitch

For really large towed Whalers a weight distributing hitch is required. These transfer some of the large tongue weight (up to 800 lbs. or more) onto the front axle of the tow vehicle and to the trailer's axles.

The mechanism of the weight distributing hitch is the lever. Long levers are attached to the drawbar portion of the hitch on the vehicle and are carried aft to the trailer, where chains exert an upward pull on them. The upward force is amplified by the lever action and works to raise the tow vehicle's drawbar, lifting it in effect, and transferring part of the tongue weight onto the front wheels of the tow vehicle. The upward pull on the levers is translated into weight shifted onto the trailer's axle(s).

Weight-distributing hitches require careful set up and adjustment. They may interfere with the operation of surge brakes, although some manufacturers assert that their products are compatible with surge break actuating systems. In the fine print of many vehicle's specifications for "Maximum Towed Weight" you will find use of a weight-distributing hitch is required to acheive the highest rated capacity.


Photo: Weight Distributing Hitch
Weight Distributing Hitch
The tongue weight is reduced by use of a weight distributing hitch like this one. The levers are pulled up and snapped into a latching mechanism under tension. This upward pull on the end of the levers is amplified by the lever action and tends to lift the drawbar side of the hitch upward. That decreases the tongue weight. The weight removed from the tongue is shifted to the front axle of the tow vehicle and the axle(s) of the trailer.
Photo credit: Larry Goltz


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Copyright © 1999, 2000 by James W. Hebert. Unauthorized reproduction prohibited!

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Author: James W. Hebert with important contributions from others with attribution in the text.
This article first appeared May 14, 2000.