Setting Tongue Load on a Trailer
| 30 November 2003
Disclaimer: If you don’t understand this procedure don’t use it. Ask for help from someone who can envision not only the procedure but the hazards. The procedure can be very helpful but it can also cause injury and/or property damage if not performed in a safe manner. If you use this procedure, you assume all risks involved and you waive any and all recourse against Carolina Regional Mustang Club and against the author.
If you haul your car on (or in) a trailer, one of the things you need to do is position the car in such a way that your load-balance places 10% to 15% of the total load on the hitch of your tow vehicle. Total load is the total of trailer weight plus car weight plus the weight of incidentals (everything else you haul in the trailer such as clothes, tools, spare parts, etc.). A tongue load of 10% to 15% is the working range for tag-along trailers. And remember that all weight you place on the hitch is removed from the gross weight of the trailer and added to the gross weight of the tow vehicle. It’s easy to overload your tow vehicle if you don’t keep this in mind.
I carry all of incidentals in the nose of my trailer so I have my load-balance set at 12% with a typical load. This gives me leeway to add weight or subtract weight from the incidental category and still remain within the overall 10% to 15% range.
So how do you set the balance without a long drawn out procedure at a public truck scale? Well, you do it on a level spot in your own driveway using bathroom scales. That’s right, bathroom scales.
Lets say you’re using a 20 foot closed trailer that weighs 3000 pounds empty. And your Mustang also weighs 3000 pounds. Add those two weights plus (say) another 600 pounds for incidentals and you have a grand total of 6600 pounds. That means you want between 660 and 990 pounds on your tow vehicle hitch. If you choose 12% as your set-point, your hitch will support 792 pounds.
Ok, you’re saying, nobody has bathroom scales that support 792 pounds. That’s right but how about 160 pounds or so? Something in that range is easily within the capability of bathroom scales. And the procedure to get into that range is relatively easy. The biggest part of the job is setting up but it’s still easier than loading-up and driving to a commercial scale.
The procedure begins with collecting all the paraphernalia your going to need. Start with the bathroom scales, add several blocks of wood with various cross-sectional dimensions, add some cinder blocks (four should work), add a piece of pipe that’s 5 to 6-feet long (2”, 2-1/2”, or 3” in diameter), and finally add two 12-inch long pieces of small diameter pipe or bar stock (something around 1/2” to 3/4” diameter is good).
With all this material gathered, follow the steps below:
1. Hook your trailer to the tow vehicle. Load your car and everything else you plan to haul in the trailer. Make sure you load to a nose-heavy state and make sure the car is blocked from rolling. For this procedure, it will be more convenient to block the car rather than leaving it in gear or setting the E-brake.
2. Stow all loading ramps and close all trailer doors.
3. If necessary, relocate the loaded trailer so it’s on fairly level ground. When the trailer is parked where you want it, chock the wheels.
4. Put safety blocks under the rear of the trailer frame. The blocks should have about 1/2 inch to 1-inch clearance from the frame. Don’t let the frame rest on the blocks. Disconnect the tow vehicle and move it out of the way so you have easy access to the coupler at the front of the trailer tongue. The blocks you put under the frame at the rear of the trailer will keep the front of the trailer from up-ending in case your load is too far to the rear.
5. Take the bathroom scales, the building blocks, the small pieces of pipe (or bar) and build a pier on each side of the hitch coupler. (See step eight for the proper location of the piers) Near the top of one pier, place the scales in the pier structure in such a way that they will read without binding and the readout is clearly visible. Put at least one board or wood block on top of the scales. Place one piece of small diameter pipe on the very top of each pier and orient it parallel to the long axis of the trailer. Make sure the piers are stable. You don't want them to collapse and you don’t want pieces flying out of them when they're under load.
6. The piers should be of approximate equal height with their tops about 4" lower than the underside of the coupler. That height will allow you to pass the 6-foot long piece of pipe (which will act as a moment arm) under the coupler perpendicular to the long axis of the trailer and rest it on top of the piers. Locate the piece of pipe so the coupler can be lowered onto it. The ends of the pipe will rest on the small diameter bar or pipe that you put on top of each pier.
7. The distance from the longitudinal centerline of the trailer to the longitudinal centerline of the small-diameter pipe on top of each pier is critical. The centerline of the small diameter pipe resting on the pier that includes the bathroom scales should be exactly three feet from the centerline of the trailer. The centerline of the small diameter pipe on top of the other pier should be exactly one foot from the longitudinal centerline. With that arrangement, the moment arm will distribute half of the total tongue weight to the pier resting on the ground and one-sixth of the total tongue weight to the pier where the scales reside.
8. With everything constructed and the moment arm in place under, but not touching, the coupler, tare the scales to zero or read the static load and use it later as a correction factor. When the tare is known, use the trailer jack to carefully lower the coupler onto the moment arm. Make sure the jack is raised fully off the ground. Now read the scales and lower the jack to raise the coupler off the moment arm. Using our hypothetical value of 792 pounds for total tongue weight when the load is balanced to 12% on the hitch, the pier spaced one foot from the tongue centerline will support 396 pounds and the one spaced three feet from the centerline will support 132 pounds. At 132 pounds load, the bathroom scales will read 132 pounds if you were able to tare to zero. If the tare was not set to zero, the scales will read 132 plus the tare correction factor.
9. If the tongue load is not at the desired balance point, reposition the car a small distance to either add or subtract weight from the tongue. Move the car by hand and be sure to block it in the new position. Again use the jack to lower the coupler onto the moment arm. Read the scales and repeat the repositioning procedure as necessary until the scales read the correct load for one-sixth of the total load you want transferred to the tow vehicle hitch. If the tare weight is not zero, remember to include the tare weight correction factor in your calculation each time you take a new reading.
10. When you reach the balance point of 12% hitch weight, mark the trailer floor in front of the front tire so you can attach a block to the trailer floor. The block will provide a positive stop against which you can place the front tire each time you load the car.
That's it. The procedure is accurate and quite easy to use. The diagram below shows a rough depiction of the pier and moment arm arrangement. The view is from the front of the coupler looking toward the trailer bed. It is not drawn to scale.
Remember to work safely and block everything that could move. You don’t want any unexpected consequences as you work through the procedure. Don’t climb in or on the trailer while the tongue is supported by the piers. As a working precaution, keep the trailer as level as possible. A level trailer makes it easier to move the car and helps assure that the car won’t suddenly move farther than you intended.
