Common Weight Distribution and Sway Control Questions

Weight Carrying: When towing a trailer with a standard ballmount, all of the trailer's tongue weight is transferred to the tow vehicle. Since the trailer hitch is attached to the vehicle frame, the additional weight in the rear will lower the back end of the vehicle while raising the front end. This means the rear axle will be handling not only the trailer tongue weight but additional load as weight is transferred from the front axle. Less weight on the front axle can lead to performance decreases in steering, traction, and stopping while also increasing trailer sway.

Weight Distributing: Weight distribution hitches add spring bars to the hitch system which are used to apply leverage between the tow vehicle and the trailer. This leverage transfers the load sitting on the rear of the vehicle to all the axles of the vehicle and trailer. With the trailer tongue and rear cargo load distributed between the axles, the vehicle is leveled off and performance is greatly increased. Weight distributing systems should be used any time the trailer weighs more than 50% of the vehicle weight.

Sizing: A weight distribution hitch will have two weight ratings, the gross trailer weight (GTW) and tongue weight (TW). The GTW capacity of the weight distribution system must exceed or match the loaded weight of the trailer. The TW rating listed on weight distributing hitches refers to trailer tongue weight plus the vehicle cargo weight behind the rear axle. It is important to match the weight distribution system tongue weight to your specific application. Using spring bars with a 1,000 lbs. TW capacity on a trailer with 400 lbs. of tongue weight while 100 lbs. of cargo is in the trunk (hitch weight = 500 lbs. total) can lead to erratic weight distributing performance. Looking at it the other way, if a weight distribution system has a 500 lbs. TW capacity with a 1,000 lbs. of weight, the system would be ineffective.

• Gross Trailer Weight (GTW) : The weight of the trailer fully loaded in its actual towing condition. GTW is measured by placing the fully loaded trailer on a vehicle scale.

• Tongue Weight (TW) : With weight distribution systems this includes the tongue weight of the trailer AND the cargo weight behind the rear axle in the vehicle. Trailer tongue weight is the downward force exerted on the hitch ball by the trailer coupler. In most cases, it is about 10 to 15 percent of the GTW.

Tongue Weight (for Weight Distribution) = trailer tongue weight + vehicle cargo load behind rear axle

Determining Trailer Tongue Weight: Measuring tongue weight on smaller trailers can be done using a bathroom scale and a box. On a level surface, place the coupler of the loaded trailer on the scale at normal towing height (Figure A). For heavier tongue weights, use the method diagrammed below.

Weight Distribution Components:

In addition to the class III, IV, or V trailer hitch on the vehicle, the weight distribution system is made up of the ballmount, spring bars (a.k.a. load bars or equalizing bars), and trailer mounted brackets. The ballmount is made up of two pieces. The shank, which slides into the trailer hitch and the ball platform which is referred to as the weight distribution head. The shank is available in different lengths with different drops and rises to allow for different trailer heights.

1. Hitch Assembly: The trailer hitch attaches to the frame underneath the vehicle and provides the 2" x 2" (or 2-1/2" x 2-1/2") receiver opening that the weight distribution shank slides into. Trailer hitches are divided up into different classes based on weight carrying capabilities. A trailer hitch needs to be classified as class III, IV, or V to be considered for a weight distribution system. A few Class III hitches are designed NOT to be used with a weight distribution system. Therefore, always check the weight capacity label that is on the trailer hitch. This sticker lists two capacities, Weight Carrying and Weight Distributing. If nothing is listed for weight distributing, then a weight distribution system can not be used.

2. Shank Assembly: The Weight Distributing Shank is the piece that slides into the hitch and provides an attachment point for the head. The shank is available in many different lengths, drops and rises. For easier and safer towing, it is necessary to have the trailer at a level height when it is hooked up to the hitch ball. The shank will allow you to do this. View our FAQ page for more information on choosing the correct ballmount height. You can also view all our available weight distributing shanks.

3. Head Assembly: The head unit holds the spring bars, provides a platform for the hitch ball, and attaches to the weight distributing shank. Weight distribution heads have a few different features to point out. The tilting mechanism, which fine tunes the weight distribution set up, is available in two different styles. The High Performance or Heavy Duty systems allow the tilt to be easily adjusted with serrated washers on the outside of the shank. The standard style systems use a pin with washers placed in between the head and the shank to control the tilt. Accessing the pin and washers can get quite tedious. However, this typically only has to be done upon initial set-up or if the trailer load changes enough to alter the coupler height.

The head can also have built-in platforms to allow for friction style sway control attachments. Many will offer only a right side attachment while some will have dual platforms which will be necessary for larger trailers (depending on the style of sway control used). The head is also made to accept different types of spring bars, round or trunnion. The round and trunnion terms refer to the end of the bars that attach to the weight distributing head. The round style bars slide up into the head and are held in place with clips. The trunnion style bars slide into the head from the side or back. The trunnion style of weight distribution is more heavy duty and can handle trailers of greater weight.

4. Spring Bar Assembly: As previously mentioned, there are two types of spring bars - round and trunnion - which refer to the end of the bars that attach to the weight distributing head. The round style bars slide up into the head and are held in place with clips. The trunnion style bars slide into the head from the side or back. Spring bars can also vary on the end opposite the trunnion or round bar end. The latest style from Draw-Tite, Hidden Hitch and Reese include built-in cams which are designed for use with Dual Cam Sway Control. The Draw-Tite, Hidden Hitch and Reese spring bars are also tapered on every side providing the ultimate in spring bar flex. The more the spring bar flexes, the more the weight distribution system will be working. When spring bars do not flex enough, the system can essentially turn off.

5. Chain and Bracket Assembly: Chain links are used to connect the spring bars to the trailer mounted brackets. The most common style is a snap-up uplift bracket. It lowers to grab the chain, then raises and snaps into position. The number of chain links is used to help determine the proper amount of tension to support the load. Space saving designs are also available that clamp to the trailer frame, or bolt to the side of the trailer frame.

Sway Control:

A popular accessory to the weight distribution system is the sway control. Trailer sway can be caused by cross winds, poor trailer loading (load too far back), or not enough spring bar tension. The use of a weight distributing hitch by itself will help improve trailer sway, but some additional products can help eliminate it. Trailer sway can be controlled with three different types of systems.

Independent friction controls have been around the longest. One side of the mechanism attaches to the trailer and the other to the weight distribution head. The steel bar with friction pad is used to slow down trailer sway. One slide bar friction control can be used for trailers up to 6,000 lbs. Anything over 6,000 lbs., and less than 10,000 lbs., will require 2 controls. Independent friction controls can also be used without a weight distribution system. Over or under tightening the sliding mechanism can render the system ineffective. [Part #3400]

Dependent sway controls are built in to weight distribution systems. They rely on the downward force of the spring bar to apply frictional resistance to brackets on the trailer tongue to combat trailer sway. This style is more consistent than the independent friction style, is easier to hook up, and over or under tightening is not a problem. This system is the only one approved for trailers with surge (hydraulic) brakes. [Part #49579, 49578, 66152, 66154, 66156, 66158]

Active sway controls also require a weight distribution system. An example of active sway controls is the Dual Cam System from Draw-Tite, Hidden Hitch and Reese which proactively and aggressively resist the start of sway by forcing the vehicle and trailer to ride in straight line. In tight turns the dual cam lifts the outside spring bar which increases towing performance by leaning the tow vehicle and trailer into the turn. The dual cam system can only work with weight distribution systems that have cams built into the spring bars. [Part #26000, 26002, and 26001]

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