Written by:

David Hosea

Last updated: November 1, 2023

This article is part two of an experiment I conducted to see which scale and process was best for me to calculate tongue weight.  In my first article, I evaluated four scales and processes to determine which tool was most accurate and which one was best for me based on attributes that included accuracy, cost, and ease of use.  You can read that article here.

In this article, I describe the specific processes and reveal the lessons learned by using each tool. 

I see a lot of documentation on tongue weight, but tongue weight is only one of the numbers we need.  We must also have the trailer weight so we can calculate the percentage of the weight carried at the tongue to know whether it is over or under loaded. 

Knowing the tongue weight and its ratio to total weight is important because if the tongue weight is too little — less than 10% of the total trailer weight – the trailer may sway back and forth and each change in direction could be more severe than the last causing an accident.  It can also reduce the tow vehicle’s rear wheel traction.  Too little tongue weight can also cause the trailer to bounce excessively, or porpoise.

If the tongue weight it too much — greater than 15% of the total trailer weight – it could reduce the tow vehicle’s steering axle weight making the vehicle harder to control, especially while turning and braking.  It could also damage the drivetrain and suspension

Tongue Weight and Weight Distribution

I use a BlueOx Sway Pro weight distribution hitch.  BlueOx explained how weight distribution hitches work by writing, “A weight distribution hitch alters the point where the load from the trailer is transferred to the vehicle. Rather than the weight being centered on the point where the trailer and vehicle connect, the weight distribution hitch distributes the weight across the axels of the vehicle and trailer.”

In other words, weight distribution hitches redistribute the combined weight of the tow vehicle and trailer, so weight may be added to the drive axle.  It is important to relieve the tension on weight distribution spring bars while calculating tongue weight to ensure that weight from the steering axle and/or the trailer axle are not added to the drive axle weight.

With that background, I’d like to get into the specific tools and processes we used to measure tongue weight for my 2022 30-foot Airstream Classic.

Bathroom Scale Method ($74.95)

• Bathroom Scale (analog, 330 pound capacity), $31.67
• 4×4, six ft., $12.88
• 1.5 x 6 inch steel pipe (2), $15.20
• Spare ¼ inch planks, $0

As the name implies, this method uses a simple bathroom scale with a couple pieces of pipe and I used a six foot 4×4 post notched to hold the post in place while resting on the pipes.  The notch at 2 feet meets the common distance used for placing the scale, but I added a notch at 3 feet for flexibility.  One of my friends has a much heavier trailer and with the notch at three feet from the jack stand, we can still use my scale and post to weigh.

Virtually all the instructions I found for measuring the tongue weight using a bathroom scale takes the measurement from the jack stand and that measurement can be taken with or without the foot plate. 

For this test, I placed one notch exactly one foot from the centerline of the jack and stacked planks under that notch until they were level with the top of the scale.  I placed the bathroom scale with the notch exactly two feet from the centerline of the jack.

This scale has a dial which allowed me to reset the scale to zero after adding the weight of the post and pipes.  Without the dial, I would have simply recorded the weight of the pipes and post and subtracted that from the reading.  Either way, the math is easy once I had the weight.  I simply multiplied the scale reading by the three-foot distance between pipes to get the tongue weight.  Here is the math…

Weight at the jack * 3 (distance between the pipes in feet) = tongue weight

266 * 3 = 798 pounds

If the tongue weight exceeded the scale’s capacity, I would have placed the scale under the notch at three feet.  With four feet between the pipes, I would have multiplied the scale weight by four.  Let’s assume that my friend’s trailer exceeded the scale’s weight capacity when measuring at the two-foot mark.  Reading the weight with four feet between the pipes, the math would be…

Weight at the jack * 4 (distance between the pipes in feet) = tongue weight

266 * 4 = 1,064

I discovered one small issue with the bathroom scale experiment.  I am accustomed to using digital devices because they are precise and easy to read, but the digital scale I used in the initial iterations of this experiment turned off after a few seconds.  If I wasn’t ready to record the weight or if I wanted to double check the reading or math, I had to reset the 4×4 post to get the scale to display again. 

That was inconvenient, so I replaced the digital scale with an analog and ran through the experiment again.

CAT scale ($19.00)

I like using the CAT scale to get my weights because I don’t have to make any assumptions, the numbers are guaranteed accurate, and I get real-time results.  I can also get the weights by interacting directly with the weigh master, but I have an option to use the Weigh My Truck app to document the entire transaction from first-weigh through all of the reweighs.  I wrote an article specifically about using CAT scales for weighing our rigs and you can read that article here (coming soon).

Sometimes, I make three passes through the CAT scale because I am interested in more than the tongue weight.  My first pass is with the rig configured as it is travelling down the road (with weight distribution) and I use the results to ensure that my configuration doesn’t exceed the axle and gross combined vehicle weights.  The next pass is with the trailer hitched, but without weight distribution.  The last pass is with the tow vehicle only.

To calculate the tongue weight on a CAT scale, make two passes over the scale.  The “first weigh” should include the tow vehicle and trailer after releasing the tension on the weight distribution springs.  Ignore the trailer axle weight and add the steering axle to the drive axle weight to get gross weight.  Then drop the trailer in the parking lot and “reweigh” the tow vehicle only.  Calculate the difference between both results to find the tongue weight.  Here are my results from recent passes over the scale.

In this example, 9,740 – 8,960 = 780 pounds of tongue weight.  By adding the tongue weight (780 pounds) to the trailer axle weight shown in CAT scale’s yellow ticket image above (8,420 pounds), I know that my trailer weight is 9,200 pounds.

Whoops.

This was my first objective hint that I had a tongue weight problem with my new Airstream.  The trailer weighs 9,200 pounds, so my tongue weight should be in a range of 920 to 1,380 pounds.  A trailer weight of 780 pounds may explain why my new rig does not feel as stable going down the road as my old one.

Etrailer

The website for etrailer scales has clear, concise instructions that include a discussion on the distance between the coupler and jack and how that can impact weight readings, correction factors (if needed), and assembly instructions for using the scale at the jack.  Their website has a link to a PDF version which you can get here. 

Using the scale was easy.

Measure tongue weight with the etrailer scale by placing the scale directly below the trailer’s coupler, then lower the coupler until the jack is completely off the ground and the trailer is completely supported by the scale.

I added a couple of planks under the scale to ensure that the ball was at the normal ride height and double-checked level by measuring how high the frame was off the floor at the front and back of the trailer. 

Alternatively, remove the foot plate from the trailer jack and replace it with the scale and foot assembly.  Unlatch the hitch from the ball and lower the jack until the trailer is completely supported by the scale and foot assembly.

At the coupler, the etrailer scale showed a tongue weight of 750 pounds, but 840 pounds when weighing at the jack.  This took me by surprise because my coupler is only 10 inches from the centerline of the jack and I did not expect a variation of almost of 100 pounds. When significant variations between weights recorded at the coupler and the jack occur, divide the weight at the coupler by the weight at the jack to get a correction factor.  My correction factor going forward will be 89.3 (750 ÷ 840 = 89.3).

Sherline

Sherline’s instruction manual covered just about every towing topic from chains, to driving in wind, and much more.  The tongue weight instructions begin on page 10 of the manual you can get here.

Like etrailer, capturing the tongue weight with Sherline was easy. Measure tongue weight with the Sherline scale by leveling and chocking the trailer, screwing the extension into the top of the cylinder, then using blocks or a floor jack to support the scale at the height of the hitch ball.  Lower the coupler until the jack is off the floor and the full weight of the trailer is on the scale.

To measure at the floor jack, ensure that the extension is removed from the scale and that the footplate is removed from the jack.  Lower the jack until the tube sits completely on the scale and the coupler is raised off the hitch ball.

At the jack, my initial result for Sherline scale read 675 pounds.  That seemed way off so I double-checked the ball height and trailer frame to ensure that the trailer was still sitting level.  It wasn’t.  The floor jack was not completely locked in, so the front of the trailer dropped about 2 inches and that made a difference. After raising the coupler again and checking the frame for level, the scale read 775 pounds.  That was in line with my expectations.

Conclusion

The scales and methods I described for measuring tongue weight are adequate, relatively easy, and except for the CAT scale, fast.

But remember that tongue weight by itself is only part of the question. 

We need to measure actual trailer weight to arrive at a meaningful number when calculating tongue weight percentage. 

So, use the scale of your choice to measure the tongue weight, but consider using the CAT scale at least once to get an accurate trailer weight.

See you down the road!

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